Growing Peppers in Protected Cultivation (Greenhouses)

Film and Polycarbonate: The Affordable Standard

This is the most common type of cover for amateur gardeners and small-scale farmers. They consist of a frame structure (metal or wood) covered with a light-transmitting material.

Film (PET, PVC): The cheapest and lightest option. Film transmits light well, but its strength and durability leave much to be desired. The service life of high-quality reinforced film with UV stabilization is 3-5 years.

1. Advantages for Peppers: Low cost, ease of installation, possibility of quick dismantling.

2. Disadvantages for Peppers: High heat and light loss, fragility (damaged by hail or strong wind), condensation buildup, which can lead to fungal disease development. For peppers, which prefer a stable microclimate, sharp temperature fluctuations in a film greenhouse can be stressful.

Twin-wall Polycarbonate: A more expensive but much more practical option. Polycarbonate sheets have a cellular structure that provides excellent thermal insulation.

1. Advantages for Peppers:

• Thermal Insulation: Due to the air pockets in the cells, polycarbonate is 3-4 times more effective at retaining heat than film. This allows planting seedlings earlier and extending the autumn season (Russo and Saltveit, 2012).
• Light Diffusion: The cellular structure diffuses direct sunlight, which is very important for peppers. This prevents sunscald on fruits and leaves, providing more uniform illumination for the plants (Wien and Stützel, 2020).
• Strength and Durability: Polycarbonate withstands significant mechanical loads, is resistant to hail and gusty winds. Its service life reaches 10-15 years.

2. Disadvantages: Higher cost compared to film; polycarbonate can become cloudy over time, reducing light transmission.

Glass Greenhouses: Durability and Light

This is a classic type of greenhouse, often used in commercial vegetable growing. They allow maximum penetration of sunlight and have the longest service life.

• Advantages for Peppers: Ideal light transmission, resistance to weather conditions, possibility of full microclimate control.
• Disadvantages: High cost, heavy weight (requires a strong foundation), fragility of glass. Glass greenhouses, as a rule, require automatic shading and ventilation systems, as they heat up strongly in summer.

Tunnels (Hoops with Covering Material) and Hotbeds

These are temporary and seasonal structures. Hotbeds are low covers (up to 1 m), most often used for protecting seedlings. Tunnels are higher arches covered with film or agro-fabric.

• Advantages for Peppers: Low cost, simple design, excellent solution for getting early harvests and protecting from frost. Tunnels can be easily moved around the site (Bosland and Votava, 2012).
• Disadvantages: Less stable microclimate: it gets very hot under the film or agro-fabric during the day, and temperatures can drop sharply at night. In tall tunnels, insufficient ventilation makes it easy to overheat the plants. The height of tunnels limits the growth of tall pepper varieties.

Net Covers (Hail and Insect Nets)

Net covers are not greenhouses in the classical sense – they do not accumulate heat and do not protect against frost. However, they play an important role in protecting peppers in hot climates.

• Application for Peppers:
• Shading: The net creates diffused light, protecting fruits and leaves from sunscald in hot regions (Wien and Stützel, 2020). This allows for larger, higher-quality fruits (Lin and Saltveit, 2012).
• Wind Protection: The net serves as an effective windbreak.
• Physical Protection from Pests: Insect nets reliably block the path of dangerous virus vectors such as aphids, thrips, and whiteflies, which is critically important in regions with a high disease pressure (Autko et al., 2012).

Which Greenhouse is Best for Peppers?

For growing peppers in most regions, the optimal choice is a twin-wall polycarbonate greenhouse. It provides the best balance between cost, durability, and microclimatic conditions. Polycarbonate protects plants from overheating, retains nighttime heat, and diffuses sunlight, perfectly matching the requirements of this demanding crop.

If your budget is limited, tall tunnels made of dense reinforced film are a good alternative. However, be prepared to monitor temperature and ventilation more carefully.

For southern regions with very bright sun and water scarcity, combining a greenhouse (film or polycarbonate) with a shading net, installed outside or inside during the hottest hours, is particularly effective. Also, in such zones, it is advisable to use insect nets on ventilation openings to protect plantings from viruses (Bosland and Votava, 2012; Akhatov et al., 2013).

Soil Requirements

Ideally, the soil in the greenhouse should be light, fertile, well-drained, and rich in organic matter. Amateur gardeners often use specially prepared soil mixtures, as in protected cultivation conditions, ordinary garden soil quickly compacts, and the risk of disease and pest accumulation multiplies.

The best soils for peppers are medium and light loams, as well as sandy loam soils. Heavy clay, saline, and acidic soils are unsuitable for this crop (Bosland and Votava, 2012). The optimal acidity (pH) of the soil solution for peppers is in the range of 6.0-6.5 (Autko et al., 2012).

Predecessors and Crop Rotation

In protected cultivation, it is especially important to follow crop rotation rules. Peppers cannot be grown after other solanaceous crops – tomatoes, potatoes, eggplants (Bosland and Votava, 2012). This rule is related to the risk of accumulating diseases common to these crops (e.g., Fusarium and Verticillium wilt, late blight) and pests in the soil. The best predecessors for peppers in a greenhouse are cucumbers, zucchini, all types of cabbage, onions, legumes, or green manure crops. It is recommended to return peppers to the same place no earlier than after 3-4 years (Bosland and Votava, 2012).

Preparing the Soil Mixture

Commercial greenhouses often use specialized soil mixes. In amateur vegetable growing, mixtures based on high-moor or lowland peat, humus, and sod soil in various proportions are widely used.

Example composition of a nutrient mixture for peppers:

• Peat (lowland, well-decomposed) – 75%
• Sod soil – 20%
• Sand or perlite (for aeration) – 5% (Autko et al., 2012)

If peat is used, its quality must meet certain requirements: degree of decomposition – up to 15%, ash content – no more than 10%, bulk density – 0.10-0.30 g/cm³, total porosity – 80-90% (Autko et al., 2012). Before use, it is recommended to steam the peat for 30 minutes at 100-120°C to destroy pathogenic microorganisms and weed seeds (Autko et al., 2012).

Disinfection (Fumigation)

This is a mandatory step, especially when reusing the greenhouse. The main goal is to destroy pathogens, pest larvae, and weed seeds that may remain in the soil.

1. Steaming: An environmentally friendly and effective method, especially for small soil volumes. The soil is treated with steam at 100-120°C for 30 minutes, which destroys most pathogenic microflora (Autko et al., 2012).

2. Chemical Fumigation: In commercial vegetable growing, methyl bromide was previously widely used for this purpose, but its use is now restricted or banned in many countries. Alternative fumigants are used instead, requiring strict adherence to instructions and safety measures (Russo and Saltveit, 2012). Chemical fumigation is generally unavailable to amateur gardeners.

3. Biological Disinfection: Inoculating the soil with beneficial microorganisms (e.g., preparations based on Trichoderma or Bacillus subtilis), which suppress pathogen development, is gaining popularity. This method is safe for humans and the environment.

Checking for Nematodes and Diseases

Before planting, it is highly recommended to conduct an agrochemical soil analysis for nutrient content (N, P, K) and pH level (Bosland and Votava, 2012). This will allow you to accurately adjust fertilizer doses.

Special attention should be paid to checking for nematodes. Root-knot nematode is one of the most dangerous pests in protected cultivation. Soil samples for nematode analysis should be taken when the soil is warm, placed in a plastic bag, protected from drying out, and sent to the laboratory as quickly as possible (Bosland and Votava, 2012). The presence of nematodes is a serious problem requiring either a long quarantine or the use of resistant rootstocks when grafting peppers.

Fertilizer Application (Soil Amendment)

Pepper is a crop demanding in terms of soil fertility. The main nutrients are applied in several stages, and their dosage depends on the composition of your soil.

Organic Fertilizers: Peppers respond well to the application of humus or well-rotted compost. However, applying fresh manure under peppers is categorically not recommended – it causes excessive green growth at the expense of fruiting and promotes disease development (Bosland and Votava, 2012). Organics are usually applied in autumn or 2-3 weeks before planting.

Mineral Fertilizers: Approximate application rates for peppers in protected cultivation are (per 1 m²):

• Nitrogen (N) – 20-30 g (as ammonium nitrate, urea)
• Phosphorus (P₂O₅) – 30-40 g (as superphosphate)
• Potassium (K₂O) – 30-40 g (as potassium sulfate or potassium nitrate)

When planting seedlings in the holes, a tablespoon of wood ash is often added – an excellent source of potassium and micronutrients (Autko et al., 2012). It is important to remember that pepper is very sensitive to chlorine, so chloride forms of potassium fertilizers should be avoided.

Biopreparations and Beneficial Microflora

Inoculating the soil with beneficial microorganisms (e.g., preparations based on Trichoderma, Bacillus spp., Pseudomonas) 1-2 weeks before planting helps create a favorable microbiological background, suppresses the development of root rots, and promotes better nutrient uptake (Autko et al., 2012; Leskovar and Kahn, 2012). This is especially relevant in protected cultivation, where soil microflora is often depleted.

The Importance of Preparatory Work

Thorough preparation of the protected cultivation area is a key step towards a healthy and bountiful pepper harvest. It includes:

• Observing crop rotation and avoiding planting after solanaceous crops.
• Creating and disinfecting the correct soil mixture.
• Balanced application of organic and mineral fertilizers.
• Using biopreparations to enhance plant immunity.

Remember, peppers do not tolerate acidic and saline soils, nor waterlogging, so ensuring good drainage is one of the most important conditions for success (Naik, 2003). By investing time in quality soil preparation, you create all the prerequisites for active growth and abundant fruiting of your peppers throughout the season.

Determining Seedling Readiness

Standard pepper seedlings ready for transplanting into protected cultivation should meet the following criteria:

• Age: 50–60 days (Autko et al., 2012; Bosland and Votava, 2012). In some cases, depending on the variety and conditions, ages of 45–70 days are acceptable (Russo, 2012, from various sources). Overgrown seedlings (older than 70 days) establish themselves worse and take longer to recover.
• Number of leaves: 6–8 true leaves (Autko et al., 2012). The plant should be well-leafed but not elongated.
• Plant height: 20–30 cm (Autko et al., 2012).
• Stem thickness: 0.6–0.8 cm (Autko et al., 2012). A thick, sturdy stem is a sign of healthy, hardened seedlings.
• Root system: Well-developed, white, encircling the root ball (when grown in cassettes or pots).
• Developmental stage: Beginning of budding or even the appearance of the first buds. This is the optimal time for transplanting, as the plant is already ready for fruiting but is not yet flowering (Autko et al., 2012). Transplanting during the flowering phase can lead to flower drop.

10–12 days before transplanting, the seedlings need to be hardened off: gradually lower the daytime temperature by 3–5°C, increase ventilation, and accustom them to direct sunlight (Autko et al., 2012). This increases the plants' resilience to transplant shock. On planting day, all diseased, weak, and plants showing signs of disease are discarded.

Planting Dates

In protected cultivation, pepper seedlings are transplanted when the soil at a depth of 10–15 cm has warmed to a stable temperature of at least 15°C, and the air in the greenhouse warms up to 20–25°C during the day (Autko et al., 2012; Bosland and Votava, 2012). In the central zone of Russia, this is usually early May for heated greenhouses and the second-third decade of May for unheated film covers (Autko et al., 2012). In more northern regions, these dates shift to late May – early June. In regions with mild climates, transplanting can be done 2–3 weeks earlier.

Planting Technique

The planting technique for peppers is crucial for their subsequent growth, as this crop does not tolerate damage to the root system and does not form adventitious roots on the buried part of the stem, unlike tomatoes (Wien and Stützel, 2020).

Key Rule: Peppers are planted at the same depth at which they grew in the seedling pot. Burying the stem above the root collar is unacceptable – this can cause stem rot and growth retardation.

Step-by-step instructions:

1. Preparing the holes: A few hours before planting, water the soil in the greenhouse thoroughly. Make holes in the prepared bed, corresponding to the volume of the seedling's root ball.

2. Watering the holes: Pour 0.5–1.5 liters of warm water (about 25–30°C) into each hole before planting (Autko et al., 2012).

3. Removing the seedlings: Carefully remove the plants from the cassettes or pots, trying not to damage the root ball. If the seedlings were grown in peat pots, plant them together with the plant, slightly tearing or breaking the walls so that roots can penetrate freely.

4. Planting: Place the plant vertically into the hole, fill it with soil so that the root collar (the transition point between the stem and roots) is at ground level. Gently press the soil around the stem to eliminate air pockets.

5. Mulching: To retain moisture and prevent soil overheating, the surface around the plant can be mulched with dry peat, humus, or sawdust (a layer of 2–3 cm) (Bosland and Votava, 2012).

Planting Schemes

The planting scheme depends on the type and vigor of the variety, as well as the plant formation system. The main principle is to provide each plant with sufficient space for nutrition and light.

• For tall (indeterminate) varieties, which are formed into 2–3 stems and require staking, wider spacing is recommended: 3.5–4 plants per 1 m² (Autko et al., 2012). Example schemes: 40×60 cm, 40×70 cm, or a double-row scheme 40+90×40 cm (Autko et al., 2012; Russo and Saltveit, 2012).
• For medium-sized (determinate) and standard varieties, increase planting density to 4–5 plants per 1 m². The scheme can be 35–40×60 cm or double-row 40+90×35 cm.
• For dwarf and ultra-early varieties, denser planting is acceptable – up to 5–6 plants per 1 m², using a 30–35×60 cm scheme (Autko et al., 2012).
• With a double-row ribbon scheme: the row spacing is usually 40–50 cm in the narrow part (between rows) and 80–90 cm in the wide part (for access and care). The distance between plants in the row is 30–40 cm (Autko et al., 2012).

Important: with high planting density, fruits may be smaller, and the risk of disease (especially gray mold) increases due to poor ventilation. At the same time, denser plantings give a higher yield per unit area (Leskovar and Kahn, 2012).

Direct Seeding in Protected Cultivation

In regions with warm climates (southern areas, subtropics), direct sowing of pepper seeds into the greenhouse soil is possible. However, this method carries greater risk and requires strict adherence to conditions:

• The soil must be warmed to +18–20°C at the seeding depth.
• Sowing is carried out 2-3 weeks later than transplanting seedlings, after the danger of return frosts has passed.
• Sowing depth – 1–1.5 cm, in well-moistened soil.
• The sowing scheme can correspond to planting schemes, but the hill method is often practiced (2–3 seeds per hole, followed by thinning and leaving the 1 strongest plant) (Wien and Stützel, 2020).

The main disadvantages of the seedless method are: slow plant development in the initial period (especially at low night temperatures), later entry into fruiting, and instability of seedlings under temperature and soil moisture fluctuations (Leskovar and Kahn, 2012). In protected cultivation with a controlled microclimate, the seedless method can be effective for late planting dates, but for early and guaranteed harvests, using seedlings is the generally accepted standard.

Temperature: The Golden Mean

Pepper is a heat-loving crop, but it tolerates neither cold nor extreme heat. Optimal temperature regimes depend on the developmental phase and the weather outside.

Table 1. Optimal temperatures for peppers in protected cultivation (according to Autko et al., 2012; Russo and Saltveit, 2012; Wien and Stützel, 2020)

Risks of deviations:

• Above 30–35°C: Pollen becomes sterile, growth stops, flowers and young ovaries drop (Bosland and Votava, 2012). In heat, evaporation accelerates, which can cause blossom-end rot of fruits and sunscald (Wien and Stützel, 2020).
• Below 15°C: Growth slows sharply, flowering stops, pollen does not germinate, leading to the formation of ugly and seedless fruits (parthenocarpy) or their complete absence (Wien and Stützel, 2020).
• Below 13°C: Growth completely stops, plants may die under prolonged exposure (Bosland and Votava, 2012).

Air Humidity: Finding the Balance

Pepper prefers moderate air humidity. The optimal range is 60–75% (Autko et al., 2012; Russo and Saltveit, 2012).

• High humidity (>80–85%): Creates ideal conditions for the development of fungal diseases (gray mold, powdery mildew) and hinders normal pollination, as pollen sticks together and does not shed. High humidity also promotes physiological disorders such as fruit "wateriness" and cracking (Autko et al., 2012).
• Low humidity (<50%): Pollen dries out and becomes unviable, leading to flower and ovary drop. Additionally, plants suffer more from heat in dry air.

To maintain humidity at an optimal level, it is important to combine proper watering (preferably drip or furrow irrigation, avoiding wetting the leaves) with active ventilation. In hot weather, misting systems (fogging) work effectively, simultaneously lowering temperature and raising humidity, creating a "cooling effect" (Russo and Saltveit, 2012).

Light and Ventilation: Breathe Freely

Lighting: Pepper is a light-loving crop. It requires high light intensity, especially during the bud formation period (Autko et al., 2012). In regions with short daylight hours and during the winter-spring period, supplemental lighting in greenhouses is desirable. However, excess direct sunlight, especially in hot regions, can be harmful. Using light-diffusing materials (twin-wall polycarbonate) or shading nets (25-50% shading during the hottest hours) helps protect plants from sunscald on fruits and overheating of leaves (Wien and Stützel, 2020). However, a drop in illumination below a certain threshold (e.g., shading more than 50%) is undesirable, as it can reduce fruit set (Wien and Stützel, 2020).

Ventilation: This is the main tool for microclimate management. Regular ventilation allows you to reduce temperature and humidity, remove stagnant air, and ensure the supply of carbon dioxide (CO₂) necessary for photosynthesis. In film greenhouses, where vents are often lacking, it is especially important to organize side ventilation. Drafts are undesirable for peppers – they disrupt pollination and weaken the plants. Therefore, open covers on the leeward side, ensuring a smooth air exchange.

Practical recommendations:

• On sunny days, when the temperature rises above 27°C, be sure to open all possible vents and doors for active ventilation.
• In hot weather (above 30°C), use shading (nets, whitewashing the glass) and, if possible, a misting system.
• In cold weather, avoid stagnation of moist air, which promotes disease outbreaks. Even at low outside temperatures, on a sunny day, the greenhouse needs short-term ventilation.
• To maintain nighttime temperature, use various methods of heat storage (water containers that heat up during the day and release heat at night).

Managing the microclimate is an art that comes with experience. The main advice: observe your plants. Wilting leaves on a hot day, yellowing edges, flower drop, the appearance of gray coating – these are all signals indicating an imbalance in temperature or humidity. Regularly check thermometer and psychrometer (for humidity measurement) readings at plant level and correct conditions promptly. Only then can you create "paradise" conditions for your peppers, allowing them to fully unleash their potential.

The Root System: Key to Understanding

To water peppers correctly, you need to understand the characteristics of their roots. The bulk of the roots (over 70-80% of active absorbing roots) is concentrated in the upper 15-30 cm layer of soil (Naik, 2003). Moreover, the pepper root system has a poor regenerative capacity – roots damaged by drying out or mechanical cultivation recover very slowly (Autko et al., 2012). This means that the soil in the greenhouse must be kept constantly moist but not wet. Sharp fluctuations from dryness to flooding are detrimental to peppers.

Consequences of Watering Errors

1. Lack of moisture:

• Growth arrest: Plants slow down or completely stop growing.
• Flower and ovary drop: This is the stage most sensitive to stress. Even a short drought during flowering can lead to massive shedding of reproductive organs (Bosland and Votava, 2012; Wien and Stützel, 2020).
• Blossom-end rot of fruits: Potassium and calcium, essential for healthy fruit formation, are absorbed only from a moist solution. When the soil dries out, the supply of these elements sharply stops, causing tissue necrosis at the fruit tip (Wien and Stützel, 2020).
• Quality reduction: Fruits become small, deformed, thin-walled, and in hot varieties, pungency may increase (Naik, 2003).

2. Excess moisture (waterlogging):

• Root rot: In waterlogged soil, root respiration is impaired; they suffocate and begin to die. This opens the way for pathogens of root rots (Fusarium, Pythium, Rhizoctonia) (Wien and Stützel, 2020).
• Creating conditions for diseases: Moisture evaporating from the soil raises air humidity, promoting fungal diseases (gray mold, powdery mildew) (Autko et al., 2012).
• Nitrogen leaching: Excess water promotes the leaching of nitrate nitrogen from the root zone, leading to nitrogen starvation of plants (Naik, 2003).

Watering Methods

1. Manual watering (with a watering can or hose): A traditional method suitable for small greenhouses. It is important to water strictly at the base, avoiding water on leaves and stems to prevent fungal infections. The water should be warm (at least 20–23°C), as cold water causes stress and shock to the roots (Autko et al., 2012).

2. Drip irrigation: This is the most efficient and recommended method for growing peppers in protected cultivation (Russo and Saltveit, 2012; Naik, 2003). Drippers deliver water directly to the root zone in small portions.

• Advantages: Water savings (up to 50% compared to other methods), water delivery precisely to the roots, maintenance of stable soil moisture, possibility of using the drip system for fertilizer application (fertigation), leaves remain dry, reducing disease risk (Naik, 2003).
• Important: Water in drip irrigation should be warm, and the system should be regularly flushed to avoid clogging of emitters.
• Sprinkling (overhead watering): This method is not recommended for peppers in protected cultivation. Wetting leaves and fruits increases air humidity, promotes the spread of bacterial spot and other diseases, and can cause sunscald on wet fruits (Bosland and Votava, 2012).

Frequency and Volume of Watering

It's impossible to give exact figures for watering frequency, as it depends on many factors: plant age, soil type, weather, growth phase. However, there are general principles:

• Guideline: The soil in the root zone should feel moist but not wet. Optimal soil moisture for peppers is 70–80% of field capacity (Naik, 2003; Bosland and Votava, 2012). Roughly, this means that if you squeeze a handful of soil from a depth of 10–15 cm, it should form a ball without crumbling, but without releasing water. If the ball crumbles, it's time to water.
• Frequency: In warm weather in film greenhouses, watering is usually done once every 2–3 days (Autko et al., 2012). In hot weather, frequency increases. In cloudy and cool weather, watering is reduced or skipped.
• Volume: The amount of water per watering should be enough to wet the upper 20–30 cm layer of soil. Usually, this is 3–5 liters per adult plant (Autko et al., 2012).
• Time of day: It is best to water peppers in the greenhouse in the first half of the day. This allows excess moisture to evaporate before the evening cool-down, significantly reducing the risk of nighttime fungal disease outbreaks (Autko et al., 2012). Evening watering is highly undesirable.

Special Watering Periods

• Immediately after planting: Seedlings are watered abundantly after transplanting (0.5–1.5 L per plant) to ensure good root-to-soil contact. The next watering is done after 5–6 days (Autko et al., 2012).
• Flowering and fruit setting: This is a critical period. The soil must not dry out; otherwise, massive flower and ovary drop will occur (Wien and Stützel, 2020).
• Fruit growth: Watering should be regular so that fruits fill evenly. Sharp changes in humidity can lead to fruit cracking (Naik, 2003).
• Before harvest: 2-3 weeks before the final harvest, watering is reduced to accelerate ripening and improve fruit color (Bosland and Votava, 2012).

Water Quality and Temperature

Peppers are very sensitive to water quality. Water should be clean, free from heavy metal salts, and have low mineralization (electrical conductivity not exceeding 1–1.5 mS/cm). Using brackish or hard water without correction can lead to soil salinization, which is especially dangerous for peppers (Naik, 2003). The most significant danger is cold water. The temperature of the water for irrigation should be at least 20–25°C (Autko et al., 2012; Naik, 2003). Watering with ice-cold water from a well or borehole is almost a guaranteed way to cause shock, growth arrest, and root rot.

Moisture Control

Experienced gardeners often use simple moisture control methods: visual inspection of plants (wilting leaves indicate water deficiency), feeling the soil, and using mulch. Mulching the soil (with dry peat, humus, straw) is an excellent way to slow down evaporation, maintain a constant temperature in the root zone, and reduce the frequency of watering (Bosland and Votava, 2012). In commercial greenhouses, special moisture sensors (tensiometers) are used to automate watering, signaling the drip irrigation system to turn on when moisture drops to a critical level (Naik, 2003).

Main Nutrients

Understanding the role of each element and its "uptake window" is key to creating an effective fertilization schedule.

Nitrogen (N) – the engine of growth.

Nitrogen is essential for actively building green mass (leaves and stems). Its maximum uptake occurs during the period before flowering starts and at the beginning of fruiting, when the plant "framework" is formed (Autko et al., 2012).

• Deficiency: Plants appear weak, leaves are small, pale green, lower leaves turn yellow and drop. Growth slows.
• Excess: Causes excessive vegetative growth ("luxuriance"), delays flowering and fruiting, increases susceptibility to diseases, and can cause flower drop (Bosland and Votava, 2012). In greenhouses, especially with low light, nitrogen excess is particularly dangerous. Therefore, nitrogen fertilization should be reduced in cloudy weather.
• Sources: Ammonium nitrate, calcium nitrate, potassium nitrate, urea. In protected cultivation, nitrate forms (calcium, potassium nitrate) are preferred as they do not acidify the soil and are absorbed faster (Wien and Stützel, 2020).

Phosphorus (P) – energy and roots.

Phosphorus plays a key role in root system development, flowering, and fruit setting. The critical uptake period is from the beginning of flowering to ovary formation (Autko et al., 2012).

• Deficiency: Leaves become dark green with a bluish or purple hue, especially on the underside. Growth slows, flowering and fruiting are delayed.
• Sources: Superphosphate (ordinary and double), monopotassium phosphate. Phosphorus is immobile in the soil, so it is recommended to apply it in sufficient quantities before planting (pre-planting amendment) or via drip irrigation in chelated form.

Potassium (K) – fruit quality.

Potassium is the main element responsible for fruit quality: their size, color, wall thickness, sugar content, and shelf life. Additionally, it increases plant resistance to drought, diseases, and temperature fluctuations. The greatest need for potassium arises from fruit setting until the end of their ripening (Autko et al., 2012; Wien and Stützel, 2020).

• Deficiency: Manifests as marginal leaf burn (yellowing and dying of leaf edges). Fruits may be small, thin-walled, and unevenly colored.
• Sources: Potassium sulfate, potassium nitrate, monopotassium phosphate. Peppers are very sensitive to chlorine, so potassium chloride is not recommended (Autko et al., 2012).

Calcium (Ca) – fruit health.

Calcium plays a crucial role in building cell walls. Its deficiency is the main cause of the common and frustrating physiological disorder blossom-end rot (Wien and Stützel, 2020). Calcium is immobile in the plant and reaches the fruits mainly via the transpiration stream.

• Factors aggravating calcium deficiency: Irregular watering (soil drying out), high air humidity, excess nitrogen, potassium, and magnesium, which are antagonists of calcium.
• Sources: Calcium nitrate (Ca(NO₃)₂) – the most accessible and effective form. It is often used in fertilizing along with potassium nitrate.

Magnesium (Mg) – photosynthesis.

Magnesium is a component of chlorophyll, so its deficiency leads to leaf chlorosis. Peppers have high demands for magnesium throughout the growing season (Autko et al., 2012). Deficiency manifests as interveinal chlorosis: leaf blades turn yellow while veins remain green.

• Sources: Magnesium sulfate (MgSO₄) – used for root and foliar applications.

Micronutrients

Peppers are very sensitive to micronutrient deficiencies, especially under high fertility conditions (Autko et al., 2012). Key micronutrients for peppers:

• Boron (B): Necessary for pollination and fruit setting. Deficiency causes flower and ovary drop, fruit deformation.
• Manganese (Mn) and Iron (Fe): Involved in chlorophyll synthesis. Their deficiency causes chlorosis of young leaves.
• Zinc (Zn) and Molybdenum (Mo): Affect enzymatic processes necessary for protein synthesis and nitrogen uptake.

To replenish micronutrients, it is convenient to use complex chelated fertilizers (e.g., "Microvit", "Tsitovit", "Crystalon"), which are applied both to the roots and to the leaves (foliar feeding).

Fertilizer Application Schedule (Top Dressing)

There are two main types of fertilizer application:

1. Basic application (pre-planting): During soil preparation, the main doses of organic (humus, compost) and phosphorus-potassium fertilizers are applied. Organics are applied at a rate of 5–10 kg/m², also adding superphosphate (30–40 g/m²) and potassium sulfate (20–30 g/m²) (Autko et al., 2012).

2. Top Dressing (application during the growing season): Performed regularly, as pepper is a crop with an extended fruiting period, and the need for nutrients changes according to growth phases.

Approximate top dressing schedule in protected cultivation (according to Autko et al., 2012; Russo, 2012):

First feeding: 7–10 days after transplanting, once the plants have adapted and started growing. The main goal is to stimulate root system and green mass growth.

• Composition (per 10 L water): 10–15 g ammonium nitrate, 20–25 g superphosphate, 10–15 g potassium sulfate. Rate: 0.5–1 L per plant.

Second feeding: During the mass flowering phase, before fruit set begins. Emphasis on phosphorus and potassium to stimulate fruit production (Autko et al., 2012).

• Composition (per 10 L water): 10–15 g ammonium nitrate, 25–30 g superphosphate, 20–25 g potassium sulfate. Rate: 1–1.5 L per plant.

Third and subsequent feedings: During mass fruiting, when fruits are filling and new ovaries are being set simultaneously. Focus on potassium and calcium for fruit quality and blossom-end rot prevention.

• Composition (per 10 L water): 5–10 g ammonium nitrate (moderately, to avoid luxuriance), 30–40 g potassium sulfate, 15–20 g calcium nitrate. Rate: 1–1.5 L per plant.

Feedings are repeated every 2–3 weeks throughout the fruiting period, alternating root and foliar applications. The number of feedings depends on soil fertility and plant condition (total 3–5 feedings per season) (Autko et al., 2012).

Foliar Feeding (via leaves)

Spraying leaves with weak fertilizer solutions is a quick and effective way to deliver nutrients, especially micronutrients, when the root system is not functioning at full capacity (e.g., during heat or cold stress).

• Calcium nitrate (1–2 g/L) – helps prevent blossom-end rot.
• Complex micronutrients (in chelated form) – help eliminate chlorosis, improve fruit set and color.
• Monopotassium phosphate (1–1.5 g/L) – during fruiting to improve fruit quality.

Important rule: carry out foliar treatments only in cloudy weather or early morning/evening to avoid leaf burn.

Signs of Nutrient Deficiency

The ability to "read" plants by their appearance will help you promptly adjust fertilization (Autko et al., 2012):

• Pale, yellowing leaf (especially from below): Nitrogen deficiency.
• Purple tint on stems and underside of leaves: Phosphorus deficiency.
• Marginal leaf burn (on edges), small fruits: Potassium deficiency.
• Interveinal chlorosis (yellowing between veins): Magnesium deficiency.
• Dark brown, sunken spot on the fruit tip: Blossom-end rot caused by calcium deficiency.
• Bud and flower drop, fruit deformation: May be caused by boron or phosphorus deficiency, or complex stress.

Fertigation

In modern greenhouses, the main method of fertilizer application is fertigation – supplying the nutrient solution through the drip irrigation system (Naik, 2003; Russo and Saltveit, 2012). This allows:

• Applying fertilizers precisely to the root zone in small doses.
• Maintaining a constant, optimal concentration of nutrients in the soil solution.
• Saving fertilizers and water (up to 30–40%).
• Minimizing the risk of root burn, often occurring with dry fertilizer application.

When using fertigation, the concentration of the nutrient solution is measured in units of electrical conductivity (EC). For peppers, the optimal EC is 1.5–2.5 mS/cm, depending on the growth phase and fruiting stage (Russo and Saltveit, 2012). The pH of the solution should be within 5.8–6.5.

Danger of Salinization

One of the biggest problems in protected cultivation is salt accumulation in the soil (salinization). Pepper is a crop sensitive to high salt content. Signs of salinization: darkening and curling of leaf edges, death of root tips, reduced yield (Naik, 2003).

• Causes: Using hard water or water with high chloride and sodium content, excessive mineral fertilizer application, insufficient drainage.
• Preventive measures: Using quality water, alternating mineral and organic feedings, regular "leaching" of the soil (abundant watering followed by drainage water removal), especially at the end of the season. In low-volume hydroponics, the salinization problem is solved by controlling EC and drainage (Russo and Saltveit, 2012).

Brief Summary:

Remember that peppers require balanced nutrition. Base your fertilizer choice on the plant's developmental stage. At the beginning of growth, focus on nitrogen; during flowering and fruiting, on potassium, phosphorus, and calcium. Regularity and moderation are the main principles of successful fertilization. It is better to apply fertilizers more often but in smaller doses than rarely and in large amounts (Autko et al., 2012). And always remember: fertilizer overdose, especially nitrogen, is much more dangerous for peppers than a slight deficiency.

Why Form Peppers in a Greenhouse?

1. Improved lighting: In a dense bush, lower leaves and fruits suffer from lack of light. Formation allows you to "open" the center of the bush to the sun (Wien and Stützel, 2020).

2. Better ventilation: Free air circulation reduces humidity in the fruit zone, which is excellent prevention against gray mold and other fungal diseases (Autko et al., 2012).

3. Redirecting nutrition: Removing excess shoots and leaves forces the plant to channel all resources into the growth and ripening of the remaining fruits. This is especially important for large-fruited varieties.

4. Ease of care and harvest: A formed plant is easier to stake, inspect for diseases, and harvest fruits from.

Characteristics of Pepper Growth

Unlike tomatoes, the pepper stem branches dichotomously (like a fork): the main shoot ends in a flower at a certain point (usually after 8-15 leaves), and two shoots develop from the two axillary buds beneath it (the so-called "fork") (Wien and Stützel, 2020; Bosland and Votava, 2012). Then each branch in turn also splits into two, and this process continues throughout the plant's life. It is these lateral shoots of the second and subsequent orders that bear the main crop.

Main Elements of Formation

Plant formation includes several operations:

1. Removing the "crown" (king) flower

This is the very first and very important step. When the plant reaches a height of 15–25 cm and begins to branch at the first "fork," one large flower often appears at the base of the fork (at the first branching point) – it is called the "crown" or "king" flower. This flower and ovary must be removed (Autko et al., 2012; Wien and Stützel, 2020).

• Why: If you leave this fruit, it will absorb the bulk of nutrients, strongly inhibiting the growth of the plant itself and the development of all other branches, which are supposed to produce the main harvest. Removing the crown flower stimulates vigorous growth of lateral shoots (Wien and Stützel, 2020).

2. Pruning suckers (choosing main stems)

After the plant has formed the first "fork" and we have removed the crown flower, we have two strong first-order shoots. Further formation depends on the variety type and desired bush architecture.

• For tall (indeterminate) varieties, especially in extended culture or tall greenhouses, it is recommended to grow the bush in 2-3 stems (Russo and Saltveit, 2012; Autko et al., 2012). For this, after the first fork, choose the 2 strongest shoots – they will become the basis of the bush. All other shoots appearing in leaf axils on the main stem below the fork are removed ("blinded"). When forming into 3 stems, one shoot located immediately under the first flower on one of the main stems is also left.
• For medium-sized and standard varieties, which are grown in a short cycle, they are often limited to two main stems, removing all other suckers.
• Suckers appearing on the two main stems must also be removed promptly (at an early stage, before they reach 5–7 cm in length), leaving only the necessary number of leaves and ovaries on them (Autko et al., 2012).

3. Pinching lateral shoots (load regulation)

Lateral shoots will appear on the main stems from the leaf axils, which will also form flowers and fruits. To avoid overloading the plant and obtain large fruits, load regulation is carried out:

• In the lower part of the plant (up to the first fork): All lateral shoots are removed ("blinded"), especially if they appear below the first branching. This ensures good ventilation at the base of the bush (Autko et al., 2012).
• In the middle and upper part of the plant: 1–2 fruits (ovaries) are left on the lateral shoots, and the shoot is pinched above 2–3 leaves after the ovary. This allows the fruits to receive enough nutrition and ripen, while the remaining leaves will "feed" this fruit.
• On the main stems, you can also pinch the growing point above the 5-6th cluster (for determinate varieties) or continue to guide them to the trellis (for indeterminate varieties).

4. Removing lower and "unnecessary" leaves

As the plant grows, the lower leaves, especially those touching the ground, begin to age, turn yellow, and function less effectively. They also create a favorable environment for disease development. Therefore, they need to be removed regularly:

• Remove leaves on the main stems below the branching point.
• Remove yellowed, diseased, or damaged leaves throughout the plant (Autko et al., 2012).
• To improve illumination and ventilation in the fruit zone, also remove leaves that excessively shade them. This is usually done as the fruits on each cluster ripen: when the fruits on the lower cluster begin to fill, the leaves beneath them are removed. But you shouldn't remove too many leaves at once (no more than 2-3 per week), so as not to deprive the plant of its photosynthesizing surface.

Staking

Since pepper stems are quite brittle and can break under the weight of the fruits, especially large-fruited varieties, they must be staked.

1. Trellis: In the greenhouse, wire or strong twine is stretched above the rows at a height of 2–2.5 m.

2. Tying each stem: Each main stem (there may be 2 or 3) is tied separately to the trellis. Use soft twine, making a loose loop around the stem (to avoid constriction as it thickens).

3. Regular twisting: As it grows, the stem is twisted around the twine (clockwise) every 10-14 days so it grows vertically and doesn't break (Russo and Saltveit, 2012).

Formation Scheme Depending on Growth Type

Frequency and Tools

Formation operations are carried out weekly or even twice a week, especially during active growth, preventing suckers from overgrowing.

• Tool: All cuts are made with a sharp, clean knife or pruners. Ideally, the tool should be disinfected after each plant (with alcohol or a potassium permanganate solution) to avoid transmitting infections. When removing suckers by hand, they should be broken off "towards yourself" to avoid leaving "stumps" where pathogens can settle.

Brief Summary:

Forming peppers is an art of balance. Your goal is to create a strong "skeleton" of the bush (2-3 strong stems) that will support the harvest. Timely removal of excess shoots, flowers, and leaves allows the plant to use its energy most efficiently, rather than wasting it on useless greenery. Remember: "Better to cut off excess once than to harvest small and ugly fruits later" (Wien and Stützel, 2020). A properly formed and staked bush is the key to plant health and a bountiful harvest of large, juicy peppers in your greenhouse.

Biology of the Pepper Flower

The pepper flower is perfect, meaning it contains both stamens (male organs producing pollen) and a pistil (female organ receiving pollen). In most cases, peppers are capable of self-pollination – pollen from the stamens lands on the stigma of the same flower (Bosland and Votava, 2012). However, in greenhouse conditions, where there is no wind or natural carriers, this process is often disrupted.

Flower structure: In peppers, the anthers of the stamens fuse into a tube, inside which the pistil is located. For pollination to occur, pollen must fall out of the anthers and land on the pistil's stigma. In the open ground, this is facilitated by plant movement from wind or insect activity.

Flowering time: Pepper flowers open mainly in the first half of the day (before noon) and remain open for about one day (Wien and Stützel, 2020). The stigma can receive pollen for 2-3 days after opening, and pollen remains viable for up to 3 days (under optimal conditions). This gives you a small "window" for carrying out pollination.

Conditions for Successful Pollination

Even when pollen is present, pollination may not occur if the microclimate conditions are unfavorable. The success of pollination is influenced by three main factors:

1. Temperature: The optimal range for pollen germination and fertilization is 20–25°C (Wien and Stützel, 2020; Bosland and Votava, 2012).

• Below 16°C: Pollen does not germinate, the pollination and fertilization process stops. Flowers may drop or produce seedless fruits (Wien and Stützel, 2020).
• Above 32–35°C: Pollen becomes sterile (unviable), also leading to a complete lack of fruit set (Bosland and Votava, 2012). In heat, even if pollen is produced, it is often defective.
• Air humidity: Optimal humidity for pollination is 60–70%.
• Too humid (>80%): Pollen becomes heavy and "sticky," does not fall out of the anthers and does not reach the stigma (Autko et al., 2012; Russo and Saltveit, 2012).
• Too dry (<50%): Pollen dries out and becomes unviable. Additionally, in dry air, the stigma quickly dries out and stops receiving pollen.
• Illumination: Abundant flowering and quality pollen are formed only under sufficient light levels. In cloudy weather or under shading, the amount of viable pollen decreases (Wien and Stützel, 2020).

How to Tell Pollination is Not Occurring?

The most obvious sign is massive flower and ovary drop (Wien and Stützel, 2020). If flowers fall off without forming an ovary, fertilization did not occur. Also, pay attention to fruit shape: if the plant produces small, distorted, thin-walled fruits without seeds, this is a typical sign of poor or incomplete pollination (parthenocarpy) (Wien and Stützel, 2020).

Methods to Improve Pollination

In protected cultivation, there are several effective methods to achieve good fruit set.

Main Pollination Problems in Greenhouses

Brief Summary:

Successful pollination of peppers in protected cultivation is the result of a balance between temperature, humidity, and physical impact on the plant. In a small greenhouse, regular shaking of plants and maintaining an optimal microclimate is quite sufficient. On a large scale, the help of bumblebees is indispensable. Remember: if you create comfortable conditions for your peppers and "help" them with pollination, they will reward you with a bountiful harvest of beautiful, uniform, and full-weight fruits.

Basic Principles of Protection in a Greenhouse

1. Observing crop rotation: Do not grow peppers in the same greenhouse after solanaceous crops (tomatoes, eggplants, potatoes). Return to the same place no earlier than after 3-4 years (Bosland and Votava, 2012).

2. Using healthy planting material: Seeds and seedlings must be free of infections. Buy seeds from reputable producers, and grow seedlings yourself or purchase from reliable nurseries.

3. Soil and tool sterilization: Regularly steam or replace the top layer of soil, disinfect garden tools, pots, and trays (Autko et al., 2012).

4. Microclimate control: Maintain optimal humidity and temperature, avoid sharp fluctuations and air stagnation. Humidity above 80% and temperature below 15°C or above 30°C are the main triggers for diseases (Wien and Stützel, 2020; Akhatov et al., 2013).

5. Timely removal of affected parts: Pick and destroy diseased leaves, shoots, and fruits, preventing them from falling on the soil. This reduces the infection reservoir in the greenhouse.

Pepper Diseases in Protected Cultivation

Main Pepper Pests in Protected Cultivation

Aphids (greenhouse, melon): Small sucking insects that extract sap from leaves and shoots. They excrete sticky "honeydew" on which sooty molds grow. They are vectors of viruses (Akhatov et al., 2013). The most common on peppers are the green peach aphid (Myzus persicae) and the melon/cotton aphid (Aphis gossypii) (Akhatov et al., 2013).

• Control: Using entomophages (lacewings, aphid midge Aphidimyza) – the most effective and safe method (Autko et al., 2012). For severe infestations – insecticide treatment (Actellik, Fitoverm, Fufanon) (Autko et al., 2012; Akhatov et al., 2013).

Whitefly (greenhouse): Small white flying insect resembling a moth. Hides on the underside of leaves. Larvae and adults suck sap from leaves, weakening the plant. Like aphids, they excrete honeydew and are vectors of viruses (Autko et al., 2012; Akhatov et al., 2013).

• Control: The most effective is the biological method – using the parasitic wasp Encarsia (Encarsia formosa). Sticky yellow traps for adults are also effective (Autko et al., 2012; Russo and Saltveit, 2012). Insecticides used include Actellik, Fitoverm, Aktara (Autko et al., 2012).

Thrips (Western flower thrips, tobacco thrips): Small (1-2 mm) insects that suck sap from leaves, stems, and fruits. Leaves acquire a silvery sheen and become covered with necrotic spots. The main danger of thrips is that they are vectors of Tomato spotted wilt virus (TSWV), which is untreatable (Akhatov et al., 2013; Autko et al., 2012).

• Control: Strict microclimate control (avoid overheating and dryness). Using entomophages (predatory mite Amblyseius cucumeris, bug Orius). For severe infestations – insecticide treatment (Actellik, Fitoverm) (Autko et al., 2012; Akhatov et al., 2013).

Spider mite: A microscopic pest (0.3-0.5 mm) feeding on sap from the underside of leaves. Signs: fine webbing on leaves and stems, leaves turn yellow and drop. Reproduces very quickly in hot, dry air (Autko et al., 2012).

• Control: Increasing air humidity (spraying), as mites dislike moisture. Using the predatory mite Phytoseiulus (Phytoseiulus persimilis) – the most effective biological agent (Autko et al., 2012). Acaricides (preparations against mites) – Fitoverm, Actellik (Autko et al., 2012).

Integrated Pest Management (IPM)

In modern vegetable growing, priority is given to Integrated Pest Management (IPM), which combines all possible methods:

1. Prevention (agrotechnical methods): Crop rotation, disinfection, healthy planting material, microclimate management.

2. Biological method: Using beneficial insects (entomophages) and microorganisms (biopreparations).

• This is the most preferred method in greenhouses, especially during the fruiting period. It is safe for humans, does not accumulate in the soil, and does not cause pest resistance (Autko et al., 2012).
• Chemical method: Use of pesticides. Used only as a last resort, when biological methods are ineffective, and strictly before flowering begins or during periods when no harvesting is taking place, to avoid toxic residues in the fruits.
• Important: In greenhouses where bumblebees are used for pollination, chemical treatments are deadly for them (Russo and Saltveit, 2012).

Recommendations for Using Biopreparations

Table: Main Diseases and Pests of Peppers in Greenhouses

Stages of Pepper Fruit Ripeness

Pepper fruits are harvested in two stages of maturity – technical and biological (Autko et al., 2012; Bosland and Votava, 2012).

• Technical (or commercial) maturity: Fruits have reached full size and the shape characteristic of the variety but have not yet acquired their final color (Bosland and Votava, 2012). They have a dark green, light green, cream, or purple hue, characteristic of the variety at this stage. Seeds in the fruits are at milky or waxy ripeness. Fruits at this stage are already fully edible, transport well, and store for a long time (up to 2-3 weeks under proper conditions) (Russo and Saltveit, 2012).
• Biological (physiological) maturity: Fruits have acquired their full varietal color – red, yellow, orange, brown, etc. Seeds are fully mature and suitable for sowing. In this phase, fruits contain the maximum amount of sugars, vitamins (especially vitamin C and carotenoids), and have the best taste (Bosland and Votava, 2012; Russo and Saltveit, 2012). However, such fruits are more delicate, transport less well, and have a shorter shelf life (no more than 1-2 weeks) (Russo and Saltveit, 2012).

In greenhouse conditions, fruits are usually harvested at technical maturity and then allowed to ripen indoors, or biological maturity is awaited on the bush (if climate and timing permit) to obtain maximum flavor and benefits. For seed production and obtaining brightly colored fruits for salads and canning, only biologically mature fruits are harvested.

Practical advice: For most pepper varieties, "colored" types (red, yellow, orange) reach biological maturity approximately 3-4 weeks after reaching technical maturity (Bosland and Votava, 2012). If the season allows, let the fruits ripen on the bush – they will be sweeter and more flavorful.

Harvesting Technique

Correct harvesting technique is important for maintaining plant health and fruit quality.

1. Harvesting time: The best time for harvesting is morning, after the dew has dried (Autko et al., 2012). At this time, fruits are most turgid, less prone to injury, and store better.

2. Tool: Use a sharp knife or pruners to harvest pepper fruits, pre-treated with a disinfectant solution (alcohol, potassium permanganate solution) to prevent disease spread (Autko et al., 2012; Russo and Saltveit, 2012).

3. Cutting the fruit: Cut the fruit together with its stem (2-3 cm), trying not to injure the plant itself. Picking fruits by hand is highly undesirable – you can break the fragile branch (Autko et al., 2012).

4. Carefulness: Handle fruits carefully to avoid damaging the skin. Damaged fruits spoil quickly and can become a source of bacterial and fungal infection for the entire harvest (Russo and Saltveit, 2012).

5. Regularity: Harvest timely. Regular harvesting stimulates the formation of new ovaries and increases overall yield. The presence of ripe fruits on the plant delays flowering and the growth of young fruits (Wien and Stützel, 2020). Harvesting frequency – 1-2 times a week (Autko et al., 2012). During mass fruiting – even more often, 2-3 times a week.

How to Extend the Fruiting Season in a Greenhouse?

In protected cultivation with proper care, peppers can bear fruit for up to 8-10 months (Russo and Saltveit, 2012). To extend the season and maximize yield, follow these recommendations:

1. Regular harvesting: Do not leave ripe fruits on the bush – this inhibits the formation of new ovaries.

2. Fertilization: Continue regular fertilizing with potassium and phosphorus fertilizers (reducing the nitrogen share) throughout the fruiting period. This supports the plant's strength.

3. Watering: Do not allow the soil to dry out, especially during hot periods. Maintain stable moisture (70-80% of field capacity).

4. Microclimate control: In late summer and autumn, pay special attention to nighttime temperatures. If they drop below 15°C, use covering material or additional greenhouse heating (Bosland and Votava, 2012). You can use heat accumulators (containers with water).

5. Lighting: In cloudy weather or in regions with short daylight hours, use supplemental lighting (HPS lamps, LED grow lights) to maintain photosynthesis and fruit set (Russo and Saltveit, 2012). Supplemental lighting is especially relevant in late autumn.

6. Removing old leaves and shoots: Regularly remove yellowed, diseased leaves and excess shoots to improve ventilation and illumination of the bush, and to direct the plant's energy into fruiting (Autko et al., 2012).

7. Pinching the tops: 1.5-2 months before the expected end of the season (e.g., at the end of September for many regions), pinch all growing points (tops) on the main stems. This redirects remaining nutrients to ripening already set fruits, rather than forming new flowers (Wien and Stützel, 2020).

8. Biological protection: Continue using biological methods for pest and disease control, as stress weakens plants and shortens the fruiting period.

Storing the Harvest

• Technically mature fruits: Stored at a temperature of 10–12°C and humidity of 90–95% for up to 2-3 weeks (Russo and Saltveit, 2012; Bosland and Votava, 2012). Lower temperatures (below 7°C) cause chilling injury (spotting, wilting).
• Biologically mature fruits: More sensitive. Stored at 7–10°C and humidity of 90–95% for no more than 1-2 weeks (Bosland and Votava, 2012; Russo and Saltveit, 2012).
• Ripening: Fruits harvested at technical maturity can be ripened to biological maturity in a dry room at a temperature of 20–25°C and humidity of 85–90% within 1-2 weeks (Bosland and Votava, 2012). Do not store peppers near apples and tomatoes – they emit ethylene, which accelerates ripening and spoilage (Russo and Saltveit, 2012).

Table: Harvesting and Storage Conditions

Brief Summary:

Timely and correct harvesting, along with proper plant care after it begins, allows you to significantly extend the pepper fruiting period in protected cultivation. Harvest fruits regularly, feed the plants, maintain an optimal microclimate, and don't forget about bush formation. As a result, you can enjoy fresh, aromatic fruits until late autumn, and with heating and supplemental lighting, even year-round. Have a successful season!

Mistake 1. Incorrect Variety Selection for the Greenhouse

The mistake: Growing varieties intended for open ground in protected cultivation, or vice versa – using greenhouse hybrids in conditions they are not suited for.

How to do it right: For greenhouses, choose varieties and hybrids specifically recommended for protected cultivation: they set fruit better under low light, are disease-resistant, and have an indeterminate (unlimited) growth type, allowing maximum yield per unit area (Russo and Saltveit, 2012; Autko et al., 2012). For small greenhouses, hybrids with determinate and semi-determinate growth, which do not require complex formation, are excellent. Always study the variety description before buying!

Mistake 2. Overcrowding Plants

The mistake: The desire to get more yield per square meter leads to planting plants too densely. This causes light deficiency, poor ventilation, high humidity inside the bush, and consequently, fungal disease outbreaks (especially gray mold). Overcrowded plants pollinate worse, and fruits become smaller (Wien and Stützel, 2020; Leskovar and Kahn, 2012).

How to do it right: Follow recommended planting schemes. For tall varieties – no more than 3.5–4 plants per 1 m²; for medium-sized – 4–5; for standard and dwarf varieties – up to 5–6 plants per 1 m² (Autko et al., 2012). Remember: "Spacious is better than cramped!". Plant formation also helps solve the overcrowding issue.

Mistake 3. Sharp Temperature Fluctuations and Drafts

The mistake: In protected cultivation, temperatures can change sharply: the greenhouse overheats during the day and cools down at night. Sharp fluctuations (more than 10–12°C per day) cause severe stress for peppers: flowers and ovaries drop, growth stops, pollen quality decreases (Wien and Stützel, 2020; Bosland and Votava, 2012). Drafts also disrupt pollination and weaken plants.

How to do it right: Strive to maintain a stable temperature regime. Optimal daytime temperature – 23–25°C, nighttime – 17–18°C (Autko et al., 2012; Russo and Saltveit, 2012). For this:

• In hot weather, ventilate the greenhouse regularly, use shading nets or whitewash the roof.
• On cold nights, cover plants with spunbond or use water containers as heat accumulators.
• Ventilate the greenhouse gradually, avoiding sharp drafts.

Mistake 4. Improper Watering – The Main Enemy

The mistake: The most common mistake is watering peppers with cold water (below 20°C). This causes root system shock, growth arrest, and root rots (Naik, 2003; Autko et al., 2012). The second mistake is irregular watering: alternating drying out and excess moisture. During drying out – flowers and ovaries drop, blossom-end rot develops; during waterlogging – roots suffocate, plants are affected by fungal diseases (Wien and Stützel, 2020).

How to do it right:

• Always use only warm water (22–25°C).
• Water regularly, avoiding both soil drying out (moisture 70-80% of field capacity) and water stagnation.
• Water should be applied at the root (preferably by drip method), without wetting the leaves.
• Water in the first half of the day so that excess moisture evaporates before evening.

Mistake 5. Excess Nitrogen Fertilizers

The mistake: Excessive use of nitrogen fertilizers (particularly manure or poultry manure infusions) leads to vigorous green growth at the expense of fruiting ("luxuriance"). Plants become "loose," more susceptible to diseases, flowering is delayed, and few ovaries form (Autko et al., 2012; Bosland and Votava, 2012).

How to do it right:

• Balance nutrition. Give nitrogen at the beginning of growth, but moderately.
• From the start of flowering and fruiting, sharply reduce the nitrogen share and increase the dose of phosphorus and potassium.
• Use complex fertilizers with micronutrients in chelated form.
• Remember: nitrogen deficiency is easier to correct with top dressing than excess.

Mistake 6. Neglecting Bush Formation

The mistake: Some gardeners believe that peppers do not need forming. As a result, impenetrable "jungles" grow in the greenhouse – with a huge leaf mass, small fruits, and high disease risk. Overcrowding prevents proper ventilation and lighting, reducing yield and fruit quality (Wien and Stützel, 2020).

How to do it right:

• Be sure to remove the "crown" (king) flower in the first fork.
• Guide the plant in 2-3 main stems.
• Regularly remove suckers (lateral shoots) and lower leaves, especially those touching the ground or turning yellow.
• Pinch lateral shoots above 1-2 ovaries to direct nutrition to the fruits.
• At the end of the season, pinch the tops of the main stems to accelerate fruit ripening.

Mistake 7. Ignoring Pollination

The mistake: In a greenhouse, where there is no wind or insect pollinators, flowers often remain unpollinated. The result is massive flower and ovary drop, as well as the formation of small, deformed, seedless fruits (Wien and Stützel, 2020; Russo and Saltveit, 2012).

How to do it right:

• Shake the plants or the wire trellis 2-3 times a week during the flowering period on sunny days.
• Use fans to create air movement.
• Install hives with bumblebees – this is the most effective method for large greenhouses.
• Maintain optimal humidity (60-70%) and temperature (20-25°C) for successful pollination.

Mistake 8. Late or Incorrect Pesticide Application

The mistake: Treating with chemical pesticides during flowering and fruiting can: 1) poison bumblebees and other pollinators, 2) make fruits toxic for humans, 3) cause burns and stress to plants. Also, chemicals are often used at the first signs of disease, forgetting about prevention (Autko et al., 2012; Russo and Saltveit, 2012).

How to do it right:

• Rely on prevention (crop rotation, healthy seeds, disinfection, microclimate control).
• Use biological preparations (Fitosporin, Trichoderma, Lepidocid) – they are safe for humans and insects.
• Apply chemical pesticides only before flowering begins or as a last resort when biological methods fail, and strictly according to the label.
• Always observe waiting periods (time until harvest) after chemical treatment.

Mistake 9. Harvesting Unripe Fruits at the End of the Season

The mistake: At the end of the season, gardeners rush and pick even unripe fruits to beat the frost. As a result, a significant part of the crop is lost, as many technically mature fruits can ripen "off the plant" (Bosland and Votava, 2012).

How to do it right:

• Before frost, collect all fruits, even the smallest ones. They can be ripened in a dry, warm room at 20–25°C and 85–90% humidity for 1-2 weeks (Bosland and Votava, 2012).
• Be sure to cut the stem, leaving 1-2 cm, and prevent rotting (remove damaged specimens).
• Unripe green fruits can be used for canning, salads, stuffing – they are still tasty and healthy.

Mistake 10. Ignoring Disease Prevention

The mistake: Many gardeners start fighting the disease only when it has already appeared, rather than when it could have been prevented. In a greenhouse, this is often too late, and the disease destroys a significant part of the harvest (Autko et al., 2012; Akhatov et al., 2013).

How to do it right:

• Regular inspection of plants is the best means of early diagnosis.
• Observe crop rotation – do not plant peppers after solanaceous crops.
• Disinfect soil (steaming, biopreparations) and tools.
• Remove diseased leaves and plants immediately.
• Control microclimate – humidity and temperature.
• Use resistant hybrids – this is your main insurance against many viruses and fungi.

Conclusion

Mistakes are part of the learning process. However, knowing the most common ones, you can avoid them and save your harvest. The main principles of successful pepper growing in protected cultivation are:

1. Healthy planting material and the right variety.

2. Moderation in everything: watering, fertilizing, overcrowding.

3. Microclimate control: stable temperature and humidity.

4. Formation and pollination – the key to abundant fruiting.

5. Prevention, rather than fighting diseases and pests.

May your greenhouse peppers delight you with a bountiful harvest of large, sweet, and aromatic fruits! Good luck!