Nutrition

Rapid Growth and Development Rate

In nature, cucumber is a vine from humid tropics, where it does not need to conserve resources. Over a short growing season, the plant forms a huge vegetative mass. Only 40–50 days pass from emergence to the start of fruiting for early‑maturing varieties (Welbaum, 2015).

Key feature: cucumber grows and fruits simultaneously. On a single plant, flowers, ovaries, and mature fruits can develop – and all of them require nutrition. This creates a constant “conveyor” demand for nutrients throughout the fruiting period.

The root system of cucumber is poorly developed compared to its above‑ground mass. Most roots are located in the topsoil layer – only 20–30 cm deep (Welbaum, 2015). Cucumber roots do not penetrate deep into the soil and cannot effectively extract nutrients from lower horizons. The plant must obtain all its nutrition from the limited soil volume in the surface layer.

A powerful above‑ground part combined with a weak root system is the main reason why cucumber is so demanding of nutrition and responds so sharply to its deficiency.

High Nutrient Uptake

At a yield of 30 t/ha, cucumber removes from the soil per hectare: nitrogen – 51 kg, phosphorus – 41 kg, potassium – 78 kg (Tarakanov & Mukhin, 2003). In terms of nutrient uptake intensity, cucumber surpasses many other vegetable crops.

Why this matters: cucumber absorbs nutrients very intensively over a short growing period. If the soil lacks sufficient available forms of elements, the plant cannot “wait” – it immediately slows growth and reduces yield.

Sensitivity to Salt Concentration

Cucumber is quite sensitive to soil salinisation. The optimal concentration of mineral salts for plants at the beginning of the growing season is 0.03–0.04%, in the middle – 0.05–0.07% (Tarakanov & Mukhin, 2003). When these values are exceeded, roots lose their ability to absorb water, and the plant wilts even with sufficient irrigation.

In simple words: cucumber prefers “soft” water and moderate nutrition, but at the same time requires that food is always on the table. This is the main challenge for the grower – to provide constant, balanced nutrition without overfeeding.

Dependence on Soil and Air Moisture

The cucumber fruit consists of 94–96% water (Autko et al., 2012). This means that the plant needs a tremendous amount of water to form the crop. But water is needed not only by itself – it serves as a transport for nutrients. Without sufficient moisture, roots cannot absorb even the fertilisers that have been applied to the soil.

Important conclusion: cucumber nutrition is inextricably linked to water supply. Irrigation is not just moistening, but a way to deliver nutrition to the roots.

Summary of the first part: Cucumber is demanding of nutrition for three main reasons:

1. Rapid growth – the plant quickly builds up mass and needs a continuous supply of elements.

2. Weak root system – roots cannot effectively obtain nutrition from deep soil layers.

3. Continuous fruiting – the plant simultaneously grows and fruits, creating a high and continuous load on the nutrition system.

In the next part, we will analyse in detail which elements cucumber needs and what role each of them plays.

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Nitrogen (N) – the Driver of Vegetative Growth

Role in the plant. Nitrogen is a component of all proteins, enzymes, chlorophyll, nucleic acids and vitamins (Mondal et al., 2020). Without it, synthesis of new cells is impossible, so nitrogen determines the rate of stem and leaf growth. For cucumber, which forms a huge leaf surface in a short time, nitrogen is the main element in the first half of the growing season.

How to recognise deficiency. With nitrogen deficiency, plants look stunted, low‑growing. Leaves first become pale, then turn yellow (chlorosis), and the process starts on the lower, older leaves and gradually moves upward. Fruits become small, misshapen, and few in number (Mondal et al., 2020). In cucumber, with acute deficiency, fruits narrow at the flower end (Mondal et al., 2020).

What happens with excess. Excess nitrogen causes lush growth of green mass at the expense of flowering and fruiting. Plants “fatten”: stems are thick, leaves dark green and large, but few ovaries are formed. In addition, excess nitrogen reduces disease resistance and impairs fruit storage (Welbaum, 2015).

What affects availability. Nitrogen is well absorbed from the soil when moisture is sufficient and temperature is above 15 °C. In cold or waterlogged soil, roots poorly absorb nitrates and ammonium. On light sandy soils, nitrogen is easily leached by rain and irrigation, so split applications are required here (Tarakanov & Mukhin, 2003).

Practical advice. Apply the main dose of nitrogen before flowering. With the onset of fruiting, reduce the proportion of nitrogen in fertilisation and increase the proportion of potassium. Use ammonium nitrate, urea, or complex fertilisers with a predominance of nitrogen. For foliar feeding, urea is better – it burns leaves less.

Phosphorus (P) – Energy and Roots

Role in the plant. Phosphorus is part of ATP (the main energy carrier), nucleic acids and many enzymes. It provides energy for all processes: respiration, cell division, transport of substances. Phosphorus is especially important for the development of the root system and the formation of generative organs – flowers and ovaries (Mondal et al., 2020).

How to recognise deficiency. Phosphorus deficiency manifests as slow growth, shortened internodes. Leaves become dark green with a bluish or purple tint (especially on the underside). Old leaves may acquire a bronze hue. Flowering and fruiting are delayed, fruits are few and small (Mondal et al., 2020).

What affects availability. Phosphorus is one of the least mobile elements in the soil. It strongly binds with calcium on alkaline soils and with aluminium and iron on acidic soils. Therefore, even when sufficient doses are applied, phosphorus may be unavailable to plants. The optimal pH for phosphorus uptake is 6.0–6.5. Cold soil also sharply reduces phosphorus absorption by roots (Welbaum, 2015).

Practical advice. Phosphorus fertilisers are better applied in advance, under autumn ploughing or in spring in rows at sowing. Use water‑soluble forms – superphosphate, ammophos. On cold soils, starter phosphorus applications in planting holes are effective. Do not mix phosphorus fertilisers with lime – phosphorus will become unavailable.

Potassium (K) – Quality and Resistance

Role in the plant. Potassium is not part of organic molecules, but it regulates water balance, stomatal opening and closing, and translocation of assimilates from leaves to fruits. It activates many enzymes and participates in protein and carbohydrate synthesis. Potassium increases drought resistance, frost resistance and disease resistance (Mondal et al., 2020). For cucumber, whose fruit is 95% water, potassium is critically important for fruit filling and taste quality.

How to recognise deficiency. Symptoms appear first on old leaves: margins and tips turn yellow, then brown and die (“scorch”). Leaves may curl downward. Fruits become deformed, with brown spots, pear‑shaped or tuberous. Sugar content decreases, fruits are watery and tasteless (Mondal et al., 2020).

What affects availability. Potassium is easily leached from light sandy soils. On clay and loamy soils it is better retained. Potassium availability decreases with excess calcium and magnesium (antagonism). Also, potassium is less absorbed in dry weather because its movement to roots depends on diffusion in the soil solution (Tarakanov & Mukhin, 2003).

Practical advice. On light soils, apply potassium in split, small doses during the period of mass fruiting. Use potassium sulphate (chlorine‑free) or potassium nitrate – they dissolve well and do not salinise the soil. Potassium chloride is best applied only in autumn so that chlorine is leached before planting. Foliar potassium applications (0.5–1% solution) are effective at the first signs of deficiency (Mondal et al., 2020).

Calcium (Ca) – Builder of Cell Walls

Role in the plant. Calcium is a structural element of cell walls (part of pectins). It provides strength and elasticity of tissues, regulates membrane permeability, and participates in cell division. Calcium also neutralises organic acids and activates some enzymes (Mondal et al., 2020).

How to recognise deficiency. In cucumber, calcium deficiency manifests primarily on young organs: the apical bud and young leaves die, leaf edges curl upward and become ragged. The most characteristic symptom is blossom‑end rot of fruits: a watery, then browning and drying spot appears at the blossom end of the fruit. Up to 75% of the crop can be affected (Mondal et al., 2020). Plants become dwarfed, internodes shortened (Tarakanov & Mukhin, 2003).

What affects availability. Calcium is immobile in the plant: it is not redistributed from old leaves to young ones, so its deficiency always appears on growing points and young fruits. Calcium uptake strongly depends on uniform irrigation: when the soil dries out, roots stop absorbing calcium, and with excess moisture, root hairs die. High sodium content in soil or irrigation water also blocks calcium (Mondal et al., 2020).

Practical advice. The main thing is to maintain stable soil moisture, avoiding sharp fluctuations. Mulching helps retain moisture. Do not apply large doses of ammonium nitrogen and fresh manure – they aggravate calcium deficiency. At the first signs of blossom‑end rot, use foliar applications of calcium nitrate or calcium chelates (this is the only way to quickly deliver calcium to the fruits). On acidic soils, add gypsum (calcium sulphate) – it does not change pH but provides available calcium.

Magnesium (Mg) – Centre of Chlorophyll

Role in the plant. Magnesium is the central element in the chlorophyll molecule. Without it, photosynthesis is impossible. It also activates many enzymes, participates in protein and carbohydrate synthesis, and in phosphorus transport (Mondal et al., 2020).

How to recognise deficiency. Symptoms appear on old (lower) leaves as interveinal chlorosis: veins remain green, but the tissue between them turns yellow. With severe deficiency, chlorosis spreads from the edges to the centre, the leaf becomes completely yellow, then brown and dies. Since magnesium is mobile, deficiency starts on lower leaves (Mondal et al., 2020).

What affects availability. Magnesium is often deficient on light acidic soils, as well as on soils with excess potassium or calcium (antagonism). High doses of potassium fertilisers can aggravate magnesium deficiency. Also, magnesium is leached from sandy areas.

Practical advice. When signs of deficiency appear, use magnesium sulphate (Epsom salt) – it can be applied to the soil (20–30 g/m²) or as a foliar spray (1–2% solution). On acidic soils, dolomite flour works well – it simultaneously reduces acidity and supplies magnesium. For prevention, include magnesium in complex fertilisers.

Sulfur (S) – Protein Builder

Role in the plant. Sulfur is part of the amino acids cysteine and methionine, as well as vitamins (biotin, thiamine) and enzymes. It participates in the synthesis of chlorophyll and proteins. Sulfur influences nitrogen assimilation – when it is deficient, even sufficient nitrogen cannot be used efficiently.

How to recognise deficiency. Symptoms resemble nitrogen deficiency: leaves become pale, light green or yellow. However, unlike nitrogen, sulfur deficiency appears first on young leaves because sulfur is immobile in the plant (Mondal et al., 2020). Growth slows, stems become thin and woody.

What affects availability. Sulfur enters the soil with organic fertilisers and is also contained in sulphate forms of mineral fertilisers (potassium sulphate, ammonium sulphate, superphosphate). On acidic soils, sulfur is well available. Deficiency is more common on sandy soils poor in organic matter, and with prolonged use of sulphur‑free fertilisers.

Practical advice. Usually sulfur comes in sufficient quantities together with sulphate‑containing fertilisers. If you use fertilisers without sulfur (e.g., urea, ammonium nitrate, potassium chloride), periodically apply potassium sulphate or ammonium sulphate. Foliar sulfur applications are not needed – soil application is sufficient.

General Principle of Balanced Nutrition

All macronutrients must be in the correct ratio. For cucumber during active fruiting, the recommended N:P:K ratio is approximately 1:0.5:1.5–2 (i.e. potassium should be higher than nitrogen) (Tarakanov & Mukhin, 2003). This balance ensures a high yield of quality fruits without excessive vegetative growth.

Quick deficiency symptom summary:

In the next chapter, we will discuss micronutrients – their role is no less important, although they are required in small doses.

If you notice signs of deficiency, do not rush with high doses – often a single foliar application of the needed element is enough to correct the situation. Remember: prevention is easier than cure. Regular small fertilisations during irrigation (fertigation) is the most reliable way to maintain optimal nutrition of cucumber at all growth stages.

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Boron (B) – Key to Pollination and Fruit Set

Role in the plant. Boron is one of the most important micronutrients for cucumber. It participates in cell division, carbohydrate and water metabolism, protein synthesis, and lignin formation (a substance that strengthens cell walls). But the main role of boron is in generative development: it stimulates pollen germination and pollen tube growth, increases fruit set. Boron also participates in seed and fruit formation and affects sugar transport (Mondal et al., 2020).

Why cucumber is especially sensitive to boron. Cucumber is a plant with a high need for pollination (in non‑parthenocarpic varieties). Even with abundant flowers, boron deficiency causes pollen to lose viability, fertilisation fails, and ovaries drop. Even in parthenocarpic hybrids, boron deficiency reduces fruit size and quality.

How to recognise deficiency. Symptoms appear primarily on young leaves and growing points:

• Apical bud dies, main stem growth stops
• Young leaves become small, thick, brittle, edges curl downward
• Chlorosis (yellowing) of tips and margins of leaves appears
• On fruits – corky areas near the peduncle, open seed cavities, fruit cracking
• Flowering weak, ovaries drop en masse
• In acute deficiency, the growing point may die (Mondal et al., 2020)

What affects boron availability:

• Light sandy soils – boron is easily leached from the root zone
• Dry conditions – with lack of moisture, boron does not reach roots
• Liming – on soils with high pH, boron availability decreases
• High doses of organic nitrogen and phosphorus – they bind boron into unavailable forms (Mondal et al., 2020)

Special feature: Boron is immobile in the plant. It is not redistributed from old leaves to young ones. Therefore, its deficiency always appears on growing points, and constant boron supply is required throughout the growing season (Mondal et al., 2020).

Practical recommendations:

• Apply boron as foliar sprays, because soil application is often ineffective (boron is quickly bound in the soil)
• Use boric acid (0.1% solution) or borax (0.2% solution) for spraying
• Apply the first spray at the budding stage, the second at the start of mass flowering, and the third during mass fruiting
• On sandy soils, boron can be applied to the soil: 2–5 kg/ha boric acid (Autko et al., 2012) or 2–5 kg/ha borax in autumn or spring before sowing
• Do not exceed dosages – excess boron is toxic (manifests as leaf margin burns)

Iron (Fe) – Driver of Photosynthesis

Role in the plant. Iron is a key element in chlorophyll synthesis, although it is not part of chlorophyll itself. It participates in electron transfer during photosynthesis and respiration, and in protein and nucleic acid synthesis. Iron is also necessary for enzymes that reduce nitrates and fix nitrogen (Mondal et al., 2020).

How to recognise deficiency. Symptoms are very characteristic and appear on young leaves:

• Interveinal chlorosis – leaf tissue between veins becomes light yellow or white, while veins remain green
• With severe deficiency, the whole leaf pales, becoming almost white
• Plant growth slows, stems become thin
• Roots also suffer – their growth and development are suppressed (Mondal et al., 2020)

Why iron is often unavailable. Iron is one of the most “problematic” elements. In the soil, it is present in large quantities, but almost always in forms unavailable to plants (oxides, hydroxides). Iron availability sharply decreases when:

• High soil pH (above 7.0) – this is the most common cause of iron chlorosis on calcareous soils
• Poor drainage and soil compaction – under anaerobic conditions, iron becomes unavailable
• High content of copper, manganese, zinc and phosphorus – their excess blocks iron uptake (antagonism) (Mondal et al., 2020)

Practical recommendations:

• The most effective means is foliar applications of iron in chelated form (Fe‑EDTA, Fe‑DTPA). Iron chelates are not bound in leaf tissues and are easily absorbed.
• For mild chlorosis – spraying with 0.2% solution of ferrous sulphate (iron vitriol) with a surfactant.
• For severe chlorosis, 2–3 treatments at 7–10‑day intervals will be needed.
• Soil application of ferrous sulphate (5 kg/ha) is effective only on very light soils; on most soils it is ineffective because iron is quickly bound (Mondal et al., 2020).
• For prevention on calcareous soils, use acidifying irrigation (weak solution of citric acid or sulphuric acid) or add sulfur to lower pH.

Manganese (Mn) – Stress Protection

Role in the plant. Manganese activates many enzymes, participates in redox processes (in particular, in photosynthesis – in the water‑splitting reaction releasing oxygen). It is also important for chlorophyll synthesis, lignin formation, and carbohydrate metabolism. Manganese increases plant resistance to diseases because it participates in the synthesis of phenolic compounds – natural protective substances (Mondal et al., 2020).

How to recognise deficiency. Symptoms appear on young leaves and resemble iron chlorosis:

• Interveinal chlorosis – tissue between veins turns yellow, veins remain green
• With severe deficiency, chlorosis turns into necrosis (tissue death), leaves may curl and die
• Unlike iron chlorosis, in manganese deficiency veins may be lighter, and chlorosis may be patchy
• Growth slows, plants become dwarfed (Mondal et al., 2020)

Manganese toxicity. Cucumber is especially sensitive to excess manganese (this is rare on ordinary soils, but possible on acidic soils or with improper fertiliser use). With excess, plant dwarfing, chlorosis followed by leaf necrosis, spotting and curling appear (Mondal et al., 2020).

What affects manganese availability:

• High soil pH (> 6.5) – manganese becomes unavailable (this is the most common cause of deficiency)
• Coastal (alkaline) soils – almost always poor in available manganese
• Excess potassium, phosphorus, iron, copper and zinc – their high levels reduce manganese availability (antagonism) (Mondal et al., 2020)

Practical recommendations:

• On soils with pH above 6.5, apply manganese only foliarly (soil application is ineffective)
• Use manganese sulphate (0.2% solution) or manganese chelates for spraying
• The optimal time is the budding and early flowering stage, when the demand for manganese is high
• On acidic soils, manganese sulphate can be applied to the soil (10 kg/ha) (Mondal et al., 2020)
• Avoid liming soils where manganese deficiency is likely
• If using micronutrient fertilisers, choose those where manganese and iron are balanced – their excess mutually inhibits uptake

Zinc (Zn) – Growth Hormone and Protection

Role in the plant. Zinc is an essential component of many enzymes and proteins, participates in the synthesis of auxins (growth hormones), chlorophyll and proteins, and in carbohydrate metabolism. It protects cell membranes from oxidation. Zinc is especially important for the formation of generative organs – flowers and fruits (Mondal et al., 2020).

How to recognise deficiency. In cucumber, symptoms are very characteristic:

• On old leaves, mosaic chlorosis appears – patchy yellowing resembling virus mosaic
• Leaves become small, thickened, brittle, with uneven edges
• Internodes shorten, the bush takes on a “rosette” appearance (shoots crowded)
• Leaf margins may die (brown necrotic areas appear)
• Flowers dry up, fruits do not set (Mondal et al., 2020)

What affects zinc availability:

• High pH (> 7.0) – zinc becomes unavailable
• Calcareous (carbonate) soils – almost always zinc‑poor
• Sandy soils with low organic matter – zinc is easily leached
• Excess copper and phosphorus – they block zinc uptake (antagonism) (Mondal et al., 2020)

Practical recommendations:

• On carbonate and alkaline soils – only foliar applications
• Use zinc sulphate (0.05% solution) or zinc chelates
• First spraying at budding stage, second at the start of fruiting
• On acidic and poor soils, zinc sulphate can be applied to the soil (25 kg/ha) together with organic matter (Mondal et al., 2020)
• Combined application of zinc with organic fertilisers (compost, manure) is effective – organics retain zinc in available form
• For prevention, use complex micronutrient fertilisers containing zinc in chelated form

Molybdenum (Mo) – Nitrogen Assimilation

Role in the plant. Molybdenum is a vital element for the enzyme nitrate reductase, which reduces nitrates to ammonium – a form of nitrogen that the plant can use for amino acid synthesis. Without molybdenum, even abundant nitrogen nutrition is useless. Molybdenum also participates in nitrogen fixation in bacteria (although cucumber is not a legume, this enzyme is also important for the plant itself). It affects chlorophyll content, chloroplast structure, and protein synthesis. Molybdenum is also necessary for normal pollen and ovary formation (Mondal et al., 2020).

How to recognise deficiency. In cucumber:

• Interveinal chlorosis on old leaves, margins turn brown
• Leaves become narrow, deformed, with curled edges
• Plants dwarfed, stunted
• Flowering weak, delayed, pollen non‑viable → few fruits
• In severe deficiency, apical bud may die (Mondal et al., 2020)

What affects molybdenum availability:

• Acidic soils (pH < 5.5) – molybdenum becomes unavailable (this is the main cause of deficiency) (Mondal et al., 2020)
• High levels of manganese and nitrate nitrogen in the soil – they interfere with molybdenum uptake
• On sandy acidic soils, deficiency is most common

Practical recommendations:

• On acidic soils, apply liming – this raises pH to 6.0–6.5 and improves molybdenum availability
• Apply molybdenum as ammonium molybdate or sodium molybdate – soil application of 1 kg/ha is sufficient (Mondal et al., 2020)
• Foliar applications (0.05% solution) are even more effective, especially at budding and flowering stages
• Do not overdo – molybdenum excess is rare, but it is toxic at high concentrations
• For prevention, use complex micronutrient fertilisers containing a small amount of molybdenum (0.01–0.02%)

Interaction of Micronutrients: Antagonism and Synergism

Micronutrients do not act in isolation. There are complex interactions between them that must be considered when fertilising.

Antagonism (one element hinders the uptake of another):

• High levels of potassium, phosphorus, iron, copper and zinc → reduce the availability of manganese (Mondal et al., 2020)
• High levels of copper and phosphorus → reduce the availability of zinc (Mondal et al., 2020)
• High levels of copper, manganese, zinc and phosphorus → reduce the availability of iron (Mondal et al., 2020)
• High levels of manganese and nitrate nitrogen → reduce the availability of molybdenum (Mondal et al., 2020)

What this means in practice:

• Do not apply all micronutrients simultaneously at high doses – they will interfere with each other
• Use balanced complex micronutrient fertilisers (manufacturers have already accounted for element compatibility)
• If you detect a deficiency of one element, check whether you have overfed its “antagonist” (e.g., manganese deficiency is often caused by excess potassium or phosphorus)
• On soils with high pH (alkaline), always expect deficiencies of iron, manganese, zinc and boron – apply them only through leaves

General Recommendations for Micronutrient Application

1. Prevention is better than cure. Regular small applications of micronutrients prevent deficiencies that are hard to correct at later stages.

2. Use chelated forms. Chelates (e.g., Fe‑EDTA, Mn‑EDTA, Zn‑EDTA) are micronutrients enclosed in an organic shell that protects them from binding in the soil and improves leaf penetration. They act faster and more effectively, especially when applied foliarly.

3. Timing of application:

• Boron – at budding and flowering (for pollination)
• Iron and manganese – at the first signs of chlorosis on young leaves (any phase)
• Zinc – at budding and the start of fruiting
• Molybdenum – at budding (for nitrogen assimilation)

4. Do not exceed concentrations. Micronutrients are toxic at overdose. Strictly follow fertiliser instructions. For foliar sprays, concentration should not exceed 0.05–0.2% for most micronutrients.

5. Check pH. On acidic soils (pH < 5.5), molybdenum and manganese are effective (if not in excess), but iron and zinc are often unavailable – they need to be applied through leaves. On alkaline soils (pH > 7), almost all micronutrients (except molybdenum) are poorly available – prefer foliar applications.

Quick micronutrient summary:

In the next chapter, we will examine how cucumber’s nutrient requirements change across growth stages and how to adapt the fertilisation scheme to each period.

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Phase 1: From Sowing to Emergence

What happens. The seed contains a reserve of nutrients sufficient for germination and formation of the first true leaves. The root system is just beginning to develop.

Nutritional requirements. In this period, external nutrition is practically not required. The plant uses the seed’s internal resources. However, it is important that phosphorus and micronutrients are available in the soil for the development of the embryonic root (Welbaum, 2015).

What you need to know. At this stage, soil temperature (not below 12–13 °C, optimally 25–30 °C) and moisture are most important. If the soil is cold, roots will not work even if fertilisers are present (Welbaum, 2015).

Practical recommendations:

• Do not apply high doses of nitrogen fertilisers before emergence – they can inhibit germination
• If the soil is poor in phosphorus, a small amount of superphosphate can be applied in rows at sowing – this stimulates root development
• Ensure good seed‑to‑soil contact and moderate moisture

Phase 2: From Emergence to the Start of Flowering (Vegetative Growth)

What happens. The plant forms its main leaf apparatus and root system. It is in this phase that the potential of the future harvest is laid. The more powerful and healthy the plant is by flowering, the more ovaries it will be able to form.

Nutritional requirements. In this period, cucumber is most demanding of nitrogen. Nitrogen ensures rapid growth of stems and leaves, formation of a powerful assimilation apparatus. Phosphorus and potassium are also needed, but nitrogen takes the lead (Tarakanov & Mukhin, 2003).

Recommended N:P:K ratio ≈ 1.5:0.5:1 (more nitrogen).

What you need to know.

• Nitrogen deficiency in this phase cannot be compensated later – the plant will not catch up in growth.
• Excess nitrogen at the end of this phase (closer to flowering) can lead to “fattening” and delayed flowering (Welbaum, 2015).
• In this phase, it is also important to ensure sufficient calcium – it is needed for building cell walls and forming strong stems.

Practical recommendations:

• Apply the main dose of nitrogen fertilisers precisely in this period.
• If the soil was well amended with organic matter in autumn, the need for additional nitrogen is reduced.
• When growing through seedlings – feed the seedlings 7–10 days after pricking out (or transplanting into cells) with a weak solution of complex fertiliser.
• In the field – give the first fertilisation 10–14 days after emergence or one week after transplanting.
• Use urea, ammonium nitrate or complex fertilisers with a predominance of nitrogen.

Phase 3: Flowering and Beginning of Fruit Set

What happens. The plant switches from vegetative growth to generative development. Flowers begin to form, then ovaries. This is a critical moment when the load on the plant sharply increases.

Nutritional requirements. Nitrogen continues to be supplied, but its proportion should decrease. Phosphorus (for flower and ovary formation) and potassium (for ovary quality and stress resistance) come to the fore. Boron plays a special role – it ensures pollination and fruit set (Mondal et al., 2020).

Recommended N:P:K ratio ≈ 1:0.8:1.2 (moderate nitrogen, higher potassium).

What you need to know.

• In this phase, it is especially important not to overfeed with nitrogen – this will cause the plant to continue growing leaves instead of forming fruits.
• Phosphorus and potassium should be in readily available forms.
• Boron is applied only foliarly – this is the most effective method (Mondal et al., 2020).
• Zinc and molybdenum are also important – they affect the formation of generative organs.

Practical recommendations:

• If you use fertigation, gradually change the solution composition – increase the proportion of potassium and phosphorus, reduce nitrogen.
• Apply the first foliar boron spray at budding (0.1% boric acid).
• Apply the second boron spray at the beginning of mass flowering.
• Ensure there is enough potassium in the soil – its deficiency in this phase will lead to massive ovary drop.
• Irrigation should be moderate and regular – moisture fluctuations in this phase are especially dangerous.

Phase 4: Mass Fruiting

What happens. The most critical phase. The plant simultaneously flowers, forms new ovaries and fills already set fruits. The load on the nutrition system is maximum. The roots must constantly supply water and nutrients to sustain this “conveyor”.

Nutritional requirements. In this phase, the main element is potassium. Potassium is responsible for fruit quality, taste, firmness, and disease resistance. It also regulates water balance, which is critically important when fruits consist of 95% water. Nitrogen is needed, but in moderate amounts to sustain growth of new shoots and fruits. Calcium – to prevent blossom‑end rot. Magnesium – to maintain photosynthesis in aging leaves (Tarakanov & Mukhin, 2003; Welbaum, 2015).

Recommended N:P:K ratio ≈ 1:0.5:1.8–2 (potassium significantly predominates).

What you need to know.

• Potassium uptake in this phase can be twice as high as nitrogen uptake.
• If potassium is insufficient, fruits will be watery, tasteless, with brown spots.
• Moisture fluctuations in this phase are especially dangerous – they cause blossom‑end rot (calcium deficiency) and fruit cracking.
• Regular irrigation (or fertigation) is a must.

Practical recommendations:

• In fertigation, increase irrigation frequency, and the solution concentration may be slightly reduced (to avoid salinisation).
• Apply potassium in every fertilisation, using potassium sulphate or potassium nitrate (chlorine‑free).
• At the first signs of blossom‑end rot – emergency foliar application of calcium nitrate or calcium chelate.
• Continue boron applications (every 7–10 days) to improve set of subsequent fruits.
• Irrigate regularly, not allowing the soil to dry out.
• In hot weather, refreshing irrigation (sprinkling) in small doses is useful to increase air humidity.

Phase 5: Growth Slowing and Senescence (End of Season)

What happens. The plant ages, the rate of new shoot and flower formation decreases. Remaining fruits ripen. Productivity declines.

Nutritional requirements. The need for all elements decreases. Nitrogen fertilisation at this stage is no longer needed – it may cause unwanted shoot growth that will not have time to produce full fruits. Potassium and phosphorus are still important for fruit ripening and quality improvement (taste, firmness) (Welbaum, 2015).

Recommended N:P:K ratio ≈ 0.5:0.5:1.5 (almost no nitrogen).

What you need to know.

• At the end of the season, fertilisation can be stopped 2–3 weeks before the final harvest.
• If autumn is cold, the root system works less effectively – foliar applications of potassium and phosphorus are effective.
• It is important to maintain uniform irrigation until the very end so that fruits do not become bitter due to stress.

Practical recommendations:

• Reduce or stop nitrogen fertilisation.
• If you plan to extend fruiting (in a greenhouse), continue to support nutrition with potassium and phosphorus, but in smaller doses.
• Foliar applications of micronutrients (especially potassium) can help the last fruits ripen.
• Irrigate as needed, but do not over‑wet the soil (this may cause root rots).

Summary Table: Growth Stages and Nutrition

Special Cases: Greenhouse and Open Field

In greenhouses (especially in winter‑spring rotations), nitrogen requirements are higher at the beginning because under low light plants form thinner stems and need support. However, excess nitrogen under weak light leads to elongation and weakening. In greenhouses with fertigation, the fertilisation schedule is more fractional and precise (Kotov & Adritskaya, 2016).

In open field on light soils, nitrogen and potassium leach faster, so more frequent but smaller doses are required. On heavy soils, fertilisers last longer, but their availability to roots may be lower due to compaction.

During cold springs (soil temperature below 15 °C), roots poorly absorb phosphorus and potassium. In such conditions, foliar applications of these elements are effective.

Main Principle: “Nutrient Shift”

Throughout the growing season, there is a gradual shift from nitrogen to potassium:

• At the beginning – nitrogen for growth
• In the middle – balance of nitrogen and potassium
• During fruiting – potassium dominates
• At the end – only potassium and phosphorus

This principle is universal for all cucumber varieties and hybrids, regardless of growing method. Following it is the key to high yields of quality fruits.

In the next part, we will consider the main fertilisation methods (root, fertigation, foliar) – when and which method is most effective.

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Root (Soil) Application

Essence of the method. Fertilisers are applied directly to the soil – in dry form (granules, powder) or as a solution. Roots absorb elements from the soil solution. This is the traditional and most common method.

Fertigation – Application of Fertilisers with Irrigation Water

Essence of the method. Fertilisers are dissolved in irrigation water and supplied to the roots through a drip irrigation system or (less often) through sprinklers. This is the most effective way to deliver nutrition to the active root zone (Autko et al., 2012).

How fertigation works.

Water from a source (well, reservoir) enters a filtration station, then through an injector (ejector unit) a fertiliser solution is dosed into the water stream, and the nutrient solution is delivered via drip tapes directly to each plant (Autko et al., 2012). Such a system allows precise dosing of each element and changing the solution composition according to growth phases.

Advantages of fertigation (Autko et al., 2012):

1. Water use efficiency – 95% (with sprinkling, evaporation and drift losses are up to 30% or more).

2. Water savings of 2.5–3 times compared to sprinkling.

3. Fertiliser uptake is significantly higher, because elements are supplied directly to the root zone and are not bound in the soil.

4. Ability to precisely regulate nutrient composition depending on the plant development stage.

5. Optimisation of soil moisture – a constant moisture level is maintained without waterlogging or drying.

6. Leaf apparatus remains dry, reducing the risk of fungal diseases.

7. Soil structure is not disturbed, and soil crust does not form.

8. Reduced weed infestation (herbicides are not needed for row spacing).

9. Labour costs are reduced by 1.5–2 times (Autko et al., 2012).

When fertigation is most effective:

• Throughout the growing season, but especially during mass fruiting, when water and nutrient demand is highest
• On light sandy soils, where nutrients are quickly leached
• In commercial greenhouse and field production with drip irrigation
• For precise management of the N:P:K ratio across growth stages

What you need to know about dosages in fertigation:

The optimal concentration of the nutrient solution for cucumber depends on the growth phase (Tarakanov & Mukhin, 2003):

• Beginning of vegetation: 0.03–0.04% (total salt concentration)
• Middle of vegetation: 0.05–0.07%
• Exceeding 0.07–0.1% poses a risk of salinisation of the root zone

Approximate daily rates for cucumber fertigation (per ha, in kg/ha a.i.) depending on phase (Autko et al., 2012):

Note: during mass fruiting, the potassium dose increases 2–3 times compared to nitrogen – it is precisely this nutrient shift that ensures high fruit quality.

What to consider in fertigation:

• Water must be clean (free of suspended matter) to avoid clogging drippers.
• Fertilisers must be fully water‑soluble and compatible with each other (not forming precipitates).
• It is recommended to use special brands of water‑soluble fertilisers (e.g., 13:12:19 + micronutrients) (Autko et al., 2012).
• In low light (winter, cloudy weather), reduce the solution concentration to avoid excessive growth.
• In good light, the concentration can be increased, but not above the recommended limits.

Foliar (Leaf) Nutrition

Essence of the method. Fertilisers are applied by spraying the leaves. Nutrients penetrate the tissues through stomata and cuticle, bypassing the root system. This is the fastest delivery method, especially for micronutrients and “emergency” correction of deficiencies (Mondal et al., 2020).

When foliar nutrition is especially effective:

• At the first signs of micronutrient deficiencies (iron chlorosis, boron deficiency, manganese, etc.)
• During periods when the root system works poorly – cold soil, waterlogging, root damage
• On soils with high pH (calcareous), where iron, manganese, zinc and boron are bound and become unavailable to roots
• At flowering and fruit‑set stages – for rapid supply of boron and zinc
• For rapid correction of potassium deficiency (foliar application of 0.5–1% potassium sulphate or potassium nitrate solution)

For which elements is foliar nutrition preferable:

• Boron – does not move in the plant, requires constant supply → spraying at budding and flowering
• Iron – poorly absorbed from soil on alkaline soils → only chelated forms via leaves
• Manganese and zinc – similarly to iron, better absorbed through leaves
• Potassium – can be quickly replenished foliarly when deficient
• Nitrogen – rarely needed foliarly, but possible (urea 0.5% solution) with weak growth

Foliar spray recipes (Mondal et al., 2020):

• Boron: 0.1% boric acid solution (1 g/l water) or 0.2% borax
• Iron: 0.2% ferrous sulphate solution – but better chelates (0.05–0.1% Fe)
• Manganese: 0.2% manganese sulphate solution
• Zinc: 0.05% zinc sulphate solution
• Potassium: 0.5–1% potassium sulphate (K₂SO₄) or potassium nitrate (KNO₃) solution
• Complex micronutrient fertilisers: according to product instructions

What you need to know about foliar applications:

• Effectiveness depends on time of day and weather: best in early morning or evening when stomata are open and the solution does not evaporate too quickly.
• Do not spray in strong heat (above 25 °C) and under direct sunlight – burns may occur.
• To improve wetting and absorption, add a surfactant (wetting agent) – it improves solution distribution and penetration into tissues.
• Concentration should not exceed the recommended – micronutrient overdose is toxic.
• When mixing several fertilisers, check their compatibility (should not form precipitates).

Specifics for cucumber:

• Cucumber is especially responsive to foliar applications of boron, iron and potassium.
• In greenhouses with high humidity, foliar applications are less effective (solution dries slowly, but stomata may be closed).
• When applying foliar, wet both sides of the leaf – the underside has more stomata.

Comparison of Fertilisation Methods and Their Combination

Practical Scheme for Combined Nutrition

In practice, a combined system is used to obtain stable cucumber yields:

1. Autumn (or spring before planting): application of organic fertilisers (manure, compost) + phosphorus and potassium fertilisers under ploughing – creation of a long‑term reserve.

2. At sowing/planting: application of a starter dose of phosphorus and potassium in rows or holes – stimulation of the root system.

3. During vegetative growth: root applications of nitrogen fertilisers (or fertigation with a higher nitrogen proportion) – formation of a powerful leaf apparatus.

4. With the onset of flowering: transition to fertigation with a gradual shift of N:P:K towards potassium + foliar applications of boron and complex micronutrients.

5. During mass fruiting: regular fertigation with high potassium content + preventive foliar applications of calcium (preventing blossom‑end rot) and micronutrients.

6. When deficiency symptoms appear: prompt foliar application of the needed element.

Conclusion on Fertilisation Methods

Each method has its niche. Root application is the foundation, creating a nutrient reserve. Fertigation is the most effective method during active growth and fruiting, allowing precise nutrient management. Foliar nutrition is a tool for quick correction, especially for micronutrients and potassium.

For large farms and greenhouse complexes, fertigation becomes the main method, supplemented by foliar treatments. For small gardens without drip irrigation, root applications of liquid fertilisers combined with foliar sprays give good results.

The main rule: combine methods to provide the cucumber with all elements at the right time and in the right form.

In the next part, we will look at which fertilisers (organic and mineral) are best to use, their strengths and weaknesses, and how to combine them correctly.

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Organic Fertilisers: The Basis of Fertility

What are organic fertilisers. For cucumber, well‑rotted manure, compost, humus, and peat‑manure mixtures are primarily important. Fresh manure is not used immediately before sowing – it can burn roots and contain weed seeds, but it can be applied in autumn.

Why cucumber especially loves organics. Among all vegetable crops, cucumber is the most responsive to organic fertilisers, especially manure (Tarakanov & Mukhin, 2003). The high effectiveness of manure is explained not only by its nutritional value. Manure:

• Improves soil structure – loosens heavy clay soils and binds light sandy soils, making them more air‑ and water‑permeable.
• Enriches soil with carbon dioxide – decomposition of organics releases CO₂, which increases the efficiency of photosynthesis (Tarakanov & Mukhin, 2003).
• Releases heat – the decomposition process of manure is accompanied by heat release, which is especially important for cucumber, a heat‑loving crop, at the beginning of the season (Welbaum, 2015).
• Activates beneficial microorganisms – organics serve as a substrate for soil biota, which converts elements into plant‑available forms.
• Acts long‑term – organics decompose gradually, providing the plant with nutrition throughout the season.

Strengths of organic fertilisers:

• Improve soil physical properties (structure, water‑holding capacity, aeration)
• Gradually release nutrients, reducing the risk of overdose
• Increase soil buffering – mitigate fluctuations in pH and salinity
• Stimulate root system development and beneficial soil microflora
• Reduce the need for frequent mineral fertilisation

Weaknesses:

• Act slowly – effects are noticeable after weeks and months, so organics are not suitable for rapid deficiency correction
• Composition is unstable – NPK content in manure varies greatly
• May contain pathogens and weed seeds (if not aged)
• Require large volumes and significant labour for application
• On light soils, decompose quickly, requiring annual renewal

Doses and timing of organic fertiliser application for cucumber:

Approximate norms for manure or compost (Tarakanov & Mukhin, 2003; Autko et al., 2012):

• On soils of average fertility: 40–60 t/ha (4–6 kg/m²)
• On humus‑poor soils: up to 80 t/ha (8 kg/m²)
• On peat‑bog soils: 80–100 t/ha (8–10 kg/m²) – such soils are especially responsive to manure

Timing:

• Autumn, under autumn ploughing or digging – preferred option. Over winter, manure partially decomposes, becomes safe for roots, and in spring the soil warms up quickly.
• Spring, 2–3 weeks before planting – permissible, but only well‑rotted manure (humus) or compost. Fresh manure is not applied in spring – it can cause root burn and increase disease development (Welbaum, 2015).

Important warning: Do not use “fertiliser with herbicide” (e.g., “Weed and Feed”) for vegetables – the herbicides in them will kill the cucumber (Autko et al., 2012).

Mineral Fertilisers: Precision and Speed

What are mineral fertilisers. These are nitrogenous (ammonium nitrate, urea, ammonium sulphate), phosphatic (superphosphate, ammophos, diammophos), potassic (potassium sulphate, potassium nitrate, potassium chloride) and complex (nitroammophoska, azophoska, special water‑soluble fertilisers for fertigation).

Why mineral fertilisers are important for cucumber. Cucumber is a crop with high growth rates and a short period of active uptake. Organics cannot always provide the required speed of element supply. Mineral fertilisers allow precise dosing of each element and rapid correction of nutrition (Tarakanov & Mukhin, 2003).

Strengths of mineral fertilisers:

• Fast‑acting – elements are available to the plant within hours after application (in solution) or within days (dry)
• Precision – you can calculate and apply exactly as much as the plant needs at a specific stage
• Controllability – the composition of fertilisation can be easily changed according to growth phase, plant condition and weather
• Convenient for fertigation – water‑soluble forms are ideal for drip irrigation systems
• Smaller storage and transport volumes compared to organics

Weaknesses:

• Do not improve soil structure, and with long‑term use may degrade it (compaction, salinisation)
• In case of overdose or improper application, can cause root burn (so‑called “fertiliser burn”)
• Easily leached from soil, especially nitrogen and potassium on light soils
• May disrupt element balance (antagonism)
• Increase the concentration of soil solution, which is dangerous for cucumber

Cucumber sensitivity to salinisation.

Cucumber is one of the most sensitive crops to high salt concentration in the soil solution (Tarakanov & Mukhin, 2003). The optimal concentration of mineral salts for cucumber plants:

• At the beginning of vegetation: 0.03–0.04%
• In the middle of vegetation: 0.05–0.07%
• Exceeding 0.07–0.1% (especially on light soils with insufficient irrigation) can cause root burn, plants become stunted, leaves darken, then yellow and die (Mondal et al., 2020).

Therefore, when applying mineral fertilisers, it is important to:

• Not exceed recommended doses
• Apply fertilisers in split doses (small portions but frequently), especially on light soils
• Ensure sufficient irrigation to dissolve and evenly distribute salts in the root zone

Approximate doses of mineral fertilisers for cucumber (Tarakanov & Mukhin, 2003; Autko et al., 2012):

At a yield of 30–40 t/ha and average soil fertility, it is recommended (in kg/ha a.i.):

Important: Specific doses should be adjusted according to soil analysis results and considering the organic matter applied. If you have applied a lot of manure (60 t/ha), mineral fertiliser doses can be reduced by 20–30%.

Choice of specific forms:

• Nitrogen: For basic application – ammonium nitrate (34% N) or ammonium sulphate (21% N + sulfur). For fertigation and top‑dressing – urea (46% N, highly soluble) or potassium nitrate (13% N + 46% K₂O).
• Phosphorus: Superphosphate simple (19–20% P₂O₅) – for basic application, especially on neutral and slightly acidic soils. For fertigation – monopotassium phosphate (52% P₂O₅ + 34% K₂O) or water‑soluble complex fertilisers.
• Potassium: Potassium sulphate (50% K₂O + sulfur) is most preferable – chlorine‑free. Potassium chloride (60% K₂O) is best applied only in autumn so that chlorine is leached by spring. Potassium nitrate (46% K₂O + 13% N) – an excellent choice for fertigation.

For fertigation, special fully water‑soluble fertilisers are used. Examples of ready‑made brands (Autko et al., 2012):

• 13:12:19 + micronutrients – for the main period (moderate nitrogen, higher potassium)
• Aquarin and analogues – according to instructions

Combination of Organic and Mineral Fertilisers

The most effective cucumber nutrition system is combined, where organics create a favourable soil background, and mineral fertilisers allow precise regulation of nutrition in critical periods (Tarakanov & Mukhin, 2003; Welbaum, 2015).

Recommended scheme:

1. Autumn: application of manure or compost (40–60 t/ha) + part of phosphorus and potassium fertilisers (e.g., 50–70% of the calculated dose) under autumn ploughing.

2. Spring: application of the remaining phosphorus and potassium fertilisers + a starter dose of nitrogen (20–30% of the calculated) before sowing or planting.

3. During the growing season: split mineral fertiliser applications (or fertigation) according to growth stages.

Example combined doses (on sod‑podzolic soils of the Non‑Black Earth region at a yield of 30–40 t/ha) (Tarakanov & Mukhin, 2003):

• Manure or compost: 40–60 t/ha (autumn)
• Ammonium nitrate: 100–150 kg/ha (in top‑dressings)
• Superphosphate: 150–250 kg/ha (autumn + spring)
• Potassium chloride: 100–150 kg/ha (autumn) or potassium sulphate: 80–120 kg/ha (spring/top‑dressing)

Microbiological Fertilisers – An Additional Tool

In recent years, biopreparations containing beneficial microorganisms have gained popularity. They can be considered as a supplement to the main nutrition, not a replacement for fertilisers (Mondal et al., 2020).

Types:

• Nitrogen fixers (Azotobacter, Azospirillum) – fix atmospheric nitrogen in plant‑available form.
• Phosphate solubilisers (Pantoea agglomerans, Pseudomonas putida, Bacillus megaterium, Glomus fasciculatum) – convert sparingly soluble phosphorus into available forms.
• Potassium mobilisers (Frateuria aurantia, Bacillus mucilaginosus) – improve potassium availability from unavailable forms (Mondal et al., 2020).

When are they effective:

• On soils poor in organic matter
• When applying high doses of phosphorus fertilisers (bacteria help to assimilate bound phosphorus)
• In organic farming systems, where the use of mineral fertilisers is limited

What you need to know: The effectiveness of biopreparations strongly depends on soil conditions (temperature, moisture, pH) and the presence of organic substrate. On cold, waterlogged or overdried soils, they work poorly. Their use does not replace the need for basic nutrition, but only increases the efficiency of fertiliser use.

Practical Recommendations for Gardeners

1. Start with organics. If possible, apply well‑rotted manure or compost under cucumbers (a bucket per 1–2 m²). This will create a good foundation and improve the soil for several years.

2. Apply mineral fertilisers in split doses. Do not try to give everything at once. Better 3–4 small top‑dressings during the season than one large one. This is especially important for nitrogen and potassium.

3. Prefer sulphate forms. Potassium sulphate and ammonium sulphate are preferable to chloride salts because cucumber is sensitive to chlorine.

4. On light sandy soils – apply fertilisers more often but in smaller doses to avoid leaching. On heavy clay soils – apply the main doses in autumn.

5. Use complex water‑soluble fertilisers for fertigation or liquid top‑dressings. They contain all macro‑ and micronutrients in the correct ratio.

6. Do not forget about micronutrients. Even with sufficient macronutrients, deficiencies of boron, iron, manganese or zinc can seriously reduce yield. They are best applied foliarly.

7. Monitor soil pH. The optimal range for cucumber is 6.0–6.5. On acidic soils (pH < 5.5), apply liming (dolomite flour, lime) – but do this in autumn, separately from manure, to avoid nitrogen losses.

8. Check irrigation water. If water is hard (high in calcium and magnesium) or contains chlorides, take this into account when choosing fertilisers and adjust dosages to avoid salinisation.

Brief chapter summary:

• Organics are the basis of fertility, improving soil structure and biology, but act slowly.
• Mineral fertilisers are a tool for rapid and precise nutrition, especially during active growth and fruiting.
• The best result is given by their sensible combination: organics in autumn, mineral top‑dressings during the season with an emphasis on potassium during fruiting.
• Microbiological preparations are a useful addition, but not a replacement for basic fertilisers.
• The main rule – do not overfeed. Better to underfeed than to overfeed, especially with nitrogen and salts in general.

In the final part, we will consider the most typical mistakes in cucumber nutrition – excess nitrogen, potassium deficiency, calcium problems, salinisation and element imbalance – and how to avoid them.

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Mistake 1. Excess Nitrogen – The Main Problem Early in the Season

Symptoms. Plants look “fattened” – stems thick, leaves large, dark green and glossy. Vegetative growth is vigorous, but flowering is delayed, few ovaries or they drop. Fruits, if they do set, are watery, with reduced sugar content, and yellow faster (Welbaum, 2015).

Why it happens. Cucumber primarily responds to nitrogen by enhanced leaf and shoot growth. If nitrogen is too high, the plant does not switch to generative development – it “thinks” that conditions are not yet suitable for fruiting. Excess nitrogen also reduces disease resistance (especially to powdery mildew and root rots) and impairs fruit storage (Tarakanov & Mukhin, 2003).

How to avoid:

• Strictly observe nitrogen fertiliser dosages. On soils rich in organic matter, nitrogen top‑dressings may not be needed at all.
• Reduce the proportion of nitrogen in top‑dressings with the onset of flowering. During fruiting, nitrogen should be minimal.
• If using fertigation, control the solution concentration – it should not exceed 0.07% total salts.
• For top‑dressings during fruiting, use fertilisers with low nitrogen content (e.g., monopotassium phosphate or potassium sulphate).

What to do if overfeeding has already occurred:

• Stop all nitrogen applications for 1–2 weeks.
• Increase the share of potassium and phosphorus fertilisers – they help balance nitrogen.
• Water abundantly to leach some nitrogen from the root zone (on light soils).
• Apply a foliar potassium spray (potassium sulphate 0.5–1%) – this stimulates the transition to fruiting.

Mistake 2. Potassium Deficiency During Fruiting

Symptoms. Marginal scorch appears on old leaves – tips and margins turn yellow, then brown and die. Leaves may curl downward. Fruits become small, deformed (pear‑shaped or tuberous), with brown spots. Fruit taste deteriorates – they are watery, lacking sweetness (Mondal et al., 2020).

Why it happens. During mass fruiting, cucumber removes more potassium than any other element. If potassium is not supplied in sufficient quantity, the plant begins to mobilise it from old leaves, causing characteristic symptoms. On light sandy soils, potassium is easily leached, aggravating the problem (Tarakanov & Mukhin, 2003).

How to avoid:

• During fruiting, maintain N:K ratio no higher than 1:1.5–2 (potassium should predominate).
• On light soils, apply potassium in split doses, each fertilisation (in fertigation – daily or every other day).
• Use potassium sulphate or potassium nitrate – they are highly soluble and chlorine‑free.
• Apply potassium chloride only in autumn – chlorine is harmful to cucumber.

What to do at the first signs of deficiency:

• Immediately apply foliar potassium sulphate (0.5–1% solution) – this is the fastest way.
• Include potassium fertilisers in every irrigation (if using fertigation) or in every liquid top‑dressing.
• On light soils, increase the frequency of applications but reduce the single dose to avoid salinisation.

Mistake 3. Calcium Deficiency and Blossom‑End Rot

Symptoms. A watery, light‑brown spot appears at the blossom end of the fruit, gradually darkening, drying and becoming sunken. The spot can enlarge, covering 25–75% of the fruit. This is not an infectious disease, but a physiological disorder caused by calcium deficiency in growing fruit tissues (Mondal et al., 2020). With severe calcium deficiency, growing points also die, young leaf margins curl and become ragged.

Why it happens. Calcium is immobile. It is not redistributed from old leaves to young ones and fruits. If calcium is not supplied continuously, fruits (especially rapidly growing ones) are left without it. Main causes of deficiency:

• Irregular irrigation – when soil dries out, roots stop absorbing calcium; when waterlogged, root hairs die (Mondal et al., 2020).
• High sodium content in soil or irrigation water – sodium competes with calcium for uptake.
• Excess ammonium nitrogen – ammonium blocks calcium uptake.
• Soil salinisation – high salt content interferes with calcium uptake (Mondal et al., 2020).

How to avoid:

• Maintain uniform soil moisture – mulching helps significantly.
• Irrigate regularly, avoiding drying out even for a short time.
• Avoid high doses of ammonium nitrogen and fresh manure.
• On saline soils – more frequent irrigation to leach salts.
• When planting on calcium‑poor soils, apply gypsum (calcium sulphate) – it does not change pH but provides available calcium.

What to do at the first signs:

• Immediately apply foliar calcium nitrate (0.5–1% solution) or calcium chelate – this is the only way to quickly deliver calcium to fruits.
• Correct the irrigation regime – it should be regular and moderate.
• Remove affected fruits – they will not recover.

Mistake 4. Soil Salinisation

Symptoms. Plants appear stunted – growth slows, leaves darken, then turn yellow at the margins and die. In severe salinisation, the plant may die. Cucumber is especially sensitive to salinisation at a young age (Mondal et al., 2020).

Why it happens. Excess fertilisers (especially nitrogen and potassium) create a high concentration of salts in the soil solution. Roots cannot absorb water – physiological drought occurs, even if the soil is moist. On light sandy soils, salinisation develops faster because salts concentrate in a small volume. In arid regions, the problem is exacerbated if irrigation water itself contains many salts (Mondal et al., 2020; Welbaum, 2015).

How to avoid:

• Strictly observe fertiliser dosages. Do not apply “by eye”.
• On light soils, apply fertilisers in split doses – small amounts but more often.
• In fertigation, control the solution concentration (not above 0.07%).
• Use good quality irrigation water. If water is hard or saline – increase irrigation rate to leach salts.
• Use organic fertilisers – they buffer salinisation.

What to do at the first signs:

• Stop all fertilisation for 1–2 weeks.
• Carry out heavy leaching irrigation – 300–400 m³/ha of water to wash salts out of the root zone.
• After leaching, resume fertilisation but at reduced doses.
• On saline soils, switch to foliar applications – they do not increase salinisation.

Mistake 5. Micronutrient Imbalance

Symptoms. Symptoms can be varied – chlorosis, dieback of growing points, fruit deformation, weak flowering. Often symptoms of deficiency of one element are caused by excess of another (antagonism).

Micronutrient antagonism (Mondal et al., 2020):

Why it happens. Ions of different metals compete for transport proteins and binding sites in roots and plant tissues. If one element is in excess, it can “displace” another from the uptake system.

How to avoid:

• Use balanced complex micronutrient fertilisers, not individual elements.
• Do not apply all micronutrients simultaneously at high doses.
• If you detect a deficiency of one micronutrient, check whether you have overfed its antagonist.
• On soils with high pH (calcareous), all micronutrients (except molybdenum) are better applied foliarly, not to the soil.

What to do if imbalance is suspected:

• Conduct a leaf analysis (if possible) – this will accurately show which elements are deficient and which are in excess.
• Stop applying all micronutrients for 1–2 weeks.
• Resume fertilisation using only balanced complex fertilisers.
• If deficiency is confirmed, apply the deficient element foliarly at the minimum dose.

Mistake 6. Improper Irrigation

Symptoms. Element deficiencies even with sufficient fertiliser application. Leaves lose turgor, turn yellow, plants are stunted. With overwatering – roots rot, leaves turn blue and die.

Why it happens. Cucumber roots absorb nutrients only from the soil solution. If the soil is dry, roots cannot absorb even those elements that are present in the soil (Welbaum, 2015). With waterlogging, roots suffocate due to lack of oxygen, root hairs die, and uptake also ceases.

How to avoid:

• Maintain soil moisture at 70–80% of field capacity throughout the growing season.
• During fruiting, moisture should be closer to 80% of field capacity (Tarakanov & Mukhin, 2003).
• Irrigate regularly, avoiding large moisture fluctuations.
• Use drip irrigation – it provides the most uniform moistening.
• Mulch the soil – this conserves moisture and prevents drying.
• Irrigate only with warm water (not below 15 °C) – cold water shocks roots and slows uptake (Autko et al., 2012).

What to do if disturbed:

• After drying – resume irrigation, but do not flood abruptly. Better several small irrigations than one heavy one.
• After waterlogging – stop irrigation, loosen the soil to improve aeration, and if possible, drain excess water.

Mistake 7. Ignoring the Plant’s Growth Stage

Symptoms. Plants flower abundantly, but ovaries do not form or drop en masse. Or plants are vigorous but produce few fruits. Or fruits are watery and tasteless despite abundant fertilisation.

Why it happens. Cucumber changes its nutrient requirements across growth stages (Chapter 4). If during fruiting you continue to give the same fertilisers as at the beginning of growth (with high nitrogen), the plant continues to build vegetative mass at the expense of fruits. Conversely, if at the beginning of growth you do not give enough nitrogen, the plant will not form a powerful leaf apparatus, and fruiting will be poor even with good potassium nutrition (Tarakanov & Mukhin, 2003).

How to avoid:

• Strictly adhere to the “nutrient shift” scheme: nitrogen → balanced complex → potassium.
• During mass fruiting, the N:P:K ratio should be approximately 1:0.5:1.8–2.
• At the first signs of deficiency or excess, promptly adjust the composition of top‑dressings.
• Use fertigation – it allows changing the nutrient composition literally every day.

General Principles for Preventing Mistakes

1. Start with soil analysis. Knowing the initial content of elements in the soil is the best basis for calculating fertiliser doses.

2. Apply fertilisers in split doses. Better 5–6 small top‑dressings than 1–2 large ones. This reduces the risk of salinisation and ensures uniform nutrition.

3. Do not skimp on potassium during fruiting. This is the most common deficiency that directly affects yield quality and quantity.

4. Regularly inspect plants. External symptoms can help you notice a problem in time and correct it before it affects the harvest.

5. Use foliar applications for quick correction. At the first signs of micronutrient or potassium deficiency, this is the most effective method.

6. Do not mix incompatible fertilisers. For example, phosphorus fertilisers with lime or calcium nitrate – insoluble precipitates form.

7. Consider weather conditions. In cold weather, roots work less effectively – reduce solution concentrations and switch to foliar applications. In hot weather, increase irrigation frequency but not concentration.

Quick Diagnostic and Action Table

Final Words

Cucumber nutrition is not a complicated science, but a system that can be mastered and successfully applied. The main thing is to understand the logic: potassium for fruits, nitrogen for leaves, micronutrients for health, proper irrigation for uptake. Observe the plants, respond to their signals, and the cucumber will reward you with a generous harvest of quality fruits.

And remember: the best fertilisation is the one you did on time, not the one you forgot to do and try to compensate with a single large dose. Uniformity and balance are the two main principles of successful cucumber nutrition.