Magnesium and Micronutrients for Tomatoes

What Key Tasks Do Micronutrients Solve?

1. Activation of immunity and stress protection. Elements like zinc and copper are involved in the synthesis of phytoalexins — the plant's own antibiotics. Manganese and copper directly influence resistance to fungal and bacterial diseases. A plant receiving a full range of micronutrients tolerates stress much more easily: sharp temperature fluctuations, drought, or waterlogging (Wien and Stützel, 2020).

2. Management of "major" nutrient uptake. Without boron and molybdenum, the plant cannot effectively absorb nitrogen and phosphorus, no matter what doses of these fertilizers you apply. Molybdenum, for example, is a key component of the enzyme nitrate reductase, which converts nitrate nitrogen into the form used to build protein (Jones, 2008). Iron and manganese are critical for photosynthesis, and therefore for the production of sugars that shape fruit flavor.

3. Formation of fruit quality. This is perhaps the most important aspect for the gardener. Boron deficiency leads to hollow fruits, deformation, and cracking. Potassium and manganese deficiency impairs coloring, causing "green shoulder" or uneven ripening. Copper and zinc are responsible for aroma and vitamin content (Heuvelink et al., 2018). Simply put, by working with micronutrients, we are working on the taste and marketable appearance of the tomato.

The Main Difference from Macronutrients

Unlike nitrogen and potassium, which are supplied in large quantities, the concentration of micronutrients in the nutrient solution or soil is minuscule. The difference between "good" and "bad" for many of them (e.g., zinc, copper, or molybdenum) lies within a range of a few parts per million (ppm). When working with them, you are not "feeding" the plant but finely tuning its internal processes.

It is important to understand that a deficiency — or, equally dangerous, an excess — of one element blocks the uptake of others. Excess phosphorus easily causes zinc and iron deficiency. Excess potassium can trigger magnesium and calcium deficiency (Ahatov, 2010). Therefore, when starting fertilization, we must always remember: the main goal is not to add "more" but to achieve a balanced ratio.

In summary: micronutrients are not a "cure" for diseases but a tool for activating the tomato's natural defense and productivity mechanisms. Your task is not to treat the plant but to create conditions in which it can realize its maximum genetic potential.

How to Tell Your Tomato Is Lacking Magnesium?

Diagnosing magnesium deficiency is one of the simplest but most important skills for a gardener. The main symptom is interveinal chlorosis on the lower, old leaves (Ahatov, 2010).

What it looks like: the leaf blade between the veins begins to turn yellow, pale, while the veins themselves and the tissue adjacent to them remain bright green. This creates a characteristic "Christmas tree" or "net" pattern. Since magnesium, like nitrogen, is a mobile element, the plant translocates it from old leaves to young leaves and fruit sets to save the crop. Therefore, the lowest leaves are the first to suffer (Heuvelink et al., 2018). With severe starvation, the leaves may take on reddish-purple hues, then turn brown and die. Symptoms are especially pronounced during the period of heavy fruiting, when the load on the plant is maximal (Atherton & Rudich, 1986).

It is critically important not to confuse this problem with others:

• Potassium (K) deficiency: With potassium, yellowing and necrosis (tissue death) start strictly from the edges of the leaf ("marginal burn"), not from the interveinal space (Jones, 2008).
• Iron (Fe) deficiency: The young upper leaves turn yellow, not the old ones. This is a fundamental difference.

Why Does Magnesium Deficiency Occur?

Usually, it is not a problem of "little magnesium in the soil" but a problem of its availability and competition.

1. Competition with potassium (K⁺). This is the most common case. Potassium and magnesium are antagonists. The more potassium fertilizers we apply (especially potassium sulfate), the harder it is for the roots to "extract" magnesium ions. Potassium essentially "clogs" the magnesium uptake channels (Atherton & Rudich, 1986). It is precisely for high yields with good flavor that we have to apply a lot of potassium, and that is why we almost always have to balance it with magnesium.

2. Acidic soils (pH < 5.5). In acidic environments, the mobility and availability of magnesium drop sharply.

3. Light sandy soils. Magnesium is easily leached from the root zone, especially during rainy seasons or with heavy irrigation.

4. Excess nitrogen (NH₄⁺). The ammonium form of nitrogen also inhibits magnesium uptake (Jones, 2008).

Magnesium Sulfate (Epsom Salt) — The Main Tool

The main and most accessible magnesium fertilizer is magnesium sulfate (MgSO₄·7H₂O), or Epsom salt. It contains 9-10% magnesium (Mg) and about 13% sulfur (S) — another important element (Hochmuth & Sideman, 2023).

Two main methods of application:

1. Root drench (watering): This is the primary method. A solution of magnesium sulfate is watered under the root. This provides a quick and lasting effect.

• Dosage for watering: 15-20 grams per 10 liters of water. Used for scheduled feeding once every 10-14 days during the period of active growth and fruit ripening.
• Foliar feeding (by leaf): Used as "first aid" when obvious symptoms appear. Foliar feeding works faster, but the effect is shorter.
• Dosage for spraying: 10-15 grams per 10 liters of water.

Important note: When mixing magnesium sulfate with other fertilizers for root feeding, especially with calcium nitrate, a precipitate forms (calcium sulfate — gypsum). These two fertilizers cannot be mixed in the same tank or concentrate. For foliar feeding, use chelated forms (if available) or separate the watering applications in time.

How to Avoid the Problem: A Strategy of Balance

Your task is not just to add magnesium but to adjust the ratio. Ideally, the ratio of potassium (K) to magnesium (Mg) in the nutrient solution should be about 5:1 or 6:1 by element mass. If you apply 50 g of potassium fertilizer (as K₂O), it is wise to "cover" it with 10-15 g of magnesium sulfate.

Remember that magnesium sulfate is not just magnesium but also sulfur, which is needed for protein synthesis and for imparting flavor to the fruits. Regular, moderate application of magnesium sulfate is the key to healthy, dark-green foliage and sweet, brightly colored fruits.

How to Recognize Iron Deficiency: Chlorosis on Young Leaves

The main and most striking symptom of iron starvation is chlorosis (yellowing) of the young, uppermost leaves (Ahatov, 2010). This is your main distinction from magnesium deficiency, which always starts from the bottom.

What it looks like: first, the interveinal space at the shoot tip becomes pale green, almost yellow or even white. At the same time, the veins themselves remain bright green for a long time — this creates a very characteristic contrasting "net pattern" (Heuvelink et al., 2018). The leaf does not turn yellow evenly but seems to "fade" between the veins. With severe deficiency, the entire leaf becomes almost white, its growth stops, and the growing points may die.

Critically important: unlike magnesium, iron is an immobile element. The plant cannot translocate it from old leaves to young ones. Therefore, symptoms always appear on the youngest growth, at the very "top" of the tomato.

Why Does Deficiency Occur? Enemy Number One — pH.

There is usually plenty of iron in the soil. But the problem is that plants can only absorb divalent iron (Fe²⁺), and in the soil it quickly oxidizes to trivalent iron (Fe³⁺) and precipitates, becoming unavailable. This process directly depends on acidity.

Main causes of iron deficiency:

1. Alkaline soil reaction (pH > 6.8). This is the main killer of iron. The higher the pH, the faster iron transforms into a form inaccessible to roots. On calcareous soils and when watering with hard water, the problem occurs constantly (Jones, 2008).

2. Waterlogging and poor aeration. When roots "suffocate" from excess moisture, their ability to absorb iron drops sharply. This is often observed in rainy summers or with frequent watering with cold water on heavy soils (Wien and Stützel, 2020).

3. Excess of other elements. High levels of manganese (Mn), zinc (Zn), copper (Cu), or phosphorus (P) block the uptake of iron (Ahatov, 2010). This is the so-called ion antagonism.

Iron Sulfate vs. Chelate: What's the Difference?

Many gardeners try to treat iron deficiency with ordinary iron sulfate (ferrous sulfate, FeSO₄). This is often useless and sometimes harmful. Why?

• Iron sulfate (inorganic salt): In solution, it quickly oxidizes and forms an insoluble precipitate, especially on alkaline soils. The plant simply cannot absorb it. It is like giving a patient a pill in a coating that does not dissolve.
• Iron chelate (Fe-EDTA, Fe-DTPA): This is iron "packaged" in an organic shell (chelate). This shell protects the Fe²⁺ ion from oxidation and helps it penetrate the leaf or root. In this form, iron is absorbed by the plant almost 100% and acts quickly (Jones, 2008).

How to Apply: A Strategy for Fast and Reliable Correction

1. Foliar feeding (by leaf) — "first aid". This is the most effective way to combat chlorosis.

• What to use: Only iron chelate! Not sulfate.
• Dosage: Strictly according to the product instructions (usually 2-5 g per 10 L of water, depending on the chelate concentration). The solution should have a slightly acidic reaction.
• Technique: Spray the upper and lower sides of young leaves thoroughly. Apply in cloudy weather or in the evening so that droplets do not cause burns.
• Result: The effect is visible within 24-48 hours — new leaves will grow green, and old ones may partially regain their color.

2. Correction of soil pH (long-term strategy). Without this, you will fight chlorosis forever.

• Check the soil pH. If it is above 6.5, apply acidic fertilizers (ammonium sulfate) or acidify the irrigation water with citric acid (1-2 g per 10 L of water to bring pH to 5.5-6.0).
• Adding peat to the planting hole or soil also helps shift the pH in the right direction.

Golden rule: For foliar feeding with iron, do not mix iron chelate with phosphorus fertilizers or calcium nitrate in the same tank — an insoluble precipitate forms, and the effect is lost.

How to Recognize Zinc Deficiency? A Distinctive Pattern on Leaves

Symptoms of zinc starvation have their own characteristic signature that distinguishes it from other chloroses.

1. Little-leaf and rosetting. This is one of the first signs. New leaves grow small, narrow, deformed, and internodes shorten. The plant tip seems to "gather" into a rosette of small leaves (Ahatov, 2010).

2. Interveinal chlorosis with "striping". On young leaves, yellowing appears between the veins, but unlike iron, this yellowing often has a striped, spotted character. In tomatoes, this can appear as light green or yellow stripes running from the base of the leaf along the midrib (Hochmuth & Sideman, 2023).

3. Bronzing and speckling. With severe deficiency, small brown or bronze spots may appear on the leaves. The leaf seems to "rust" (Atherton & Rudich, 1986).

4. Flowering problems. Flowers may be underdeveloped, small, and fruit sets may drop. Even if fruit sets, it may be deformed or hollow.

Remember: zinc, like iron, is an immobile element, so all symptoms appear on the young growth, at the top of the plant.

The Main Trap: Zinc and Phosphorus — Dangerous Antagonism

This is one of the most common and insidious causes of zinc deficiency in tomatoes. Zinc and phosphorus are antagonists. The higher the level of phosphorus in the soil or in the plant itself, the worse zinc is absorbed (Jones, 2008).

In practice, it looks like this: the gardener generously applies superphosphate or complex fertilizers with high phosphorus content, hoping for powerful fruits. As a result, they get a pale top and small leaves — symptoms of zinc starvation. Phosphorus essentially "locks" zinc in the soil, making it unavailable.

Important: The critical level of zinc content in tomato leaves for normal growth is about 15-20 ppm (mg/kg). Dropping below this mark is guaranteed to affect the yield (Jones, 2008).

What to Do? A Strategy for Prevention and Treatment

1. Control phosphorus. Do not apply phosphorus fertilizers "by eye" or without soil analysis. On old, cultivated plots, phosphorus is often already sufficient. Use starter fertilizers with reduced phosphorus content for seedlings, and for adult plants, use potassium-nitrogen mixtures.

2. Foliar feeding (by leaf) — "first aid". This is the fastest way to deliver zinc to the plant, bypassing competitive struggle with phosphorus in the soil.

• What to use: Zinc sulfate (ZnSO₄) or, better, zinc chelate for more efficient absorption.
• Dosage: For zinc sulfate — 5-10 grams per 10 liters of water. For chelates — strictly according to instructions.
• Technique: Spray young leaves and growing points thoroughly. Apply in cloudy weather or in the evening. Repeat 2-3 times at intervals of 7-10 days.
• Root feeding. Can be used as a preventive measure but is less effective on alkaline soils due to zinc binding.
• Dosage: 10-20 grams of zinc sulfate per 10 liters of water. Water under the root.

Golden rule: When working with zinc, remember that spraying young leaves gives the best result. Old leaves will not recover with zinc, but new ones will grow healthy.

How to Distinguish Manganese Deficiency from Iron Deficiency?

This is a classic diagnostic challenge for the gardener. Both elements cause chlorosis of young leaves, but the pattern is different. Remember the main rule:

• Iron deficiency (Fe): Almost the entire leaf blade turns yellow, veins remain bright green — a sharp contrast, a "net" (Jones, 2008).
• Manganese deficiency (Mn): Yellowing or paleness occurs between veins, but veins do not remain perfectly green; they also lighten, though more slowly. The contrast is not as sharp. In addition, small brown or gray necrotic spots appear on the yellow areas — this is tissue death (Ahatov, 2010).

Simply put: with iron deficiency, the leaf looks like a "green net on a yellow background," and with manganese deficiency, it looks like a "yellow-green leaf with brown freckles." These spots (necrosis) are the key sign distinguishing manganese from other chloroses (Heuvelink et al., 2018).

Important clarification: unlike iron and zinc, manganese has moderate mobility. Symptoms more often appear on middle and young leaves but can also affect older leaves with severe starvation.

Why Is Manganese So Important for Disease Resistance?

Manganese is a key activator of enzymes involved in the synthesis of phenolic compounds — natural antiseptics of plants. These substances help the tomato fend off attacks by pathogens of dangerous diseases such as late blight, cladiosporiosis (brown spot), and gray mold (Wien and Stützel, 2020). A plant supplied with manganese "closes" its cell walls to pathogen penetration. Therefore, combating manganese deficiency is not only fertilization but also an important element of crop protection.

Causes of Manganese Deficiency

1. Alkaline soil reaction (pH > 6.8). Like iron, manganese becomes unavailable in alkaline environments. This is the main cause.

2. Waterlogging and poor aeration. In flooded, oxygen-poor soil, manganese availability drops sharply (Ahatov, 2010).

3. Heavy, compacted soils. Roots cannot develop normally and absorb elements.

4. Excess iron (Fe) or copper (Cu). These elements are antagonists of manganese and can block its uptake (Jones, 2008).

How to Apply: Choosing the Form

As with other micronutrients, the form matters.

• Manganese sulfate (MnSO₄). The most accessible and simple form for root feeding and prevention.
• Manganese chelate. Recommended for foliar feeding and when obvious deficiency symptoms appear, especially on alkaline soils where sulfate can quickly bind.

Application Strategy:

1. Foliar feeding (by leaf) — for quick correction.

• What to use: Manganese sulfate (you can add a little citric acid to acidify the solution) or chelate. @ln-latin[]
• Dosage: 5-10 grams of manganese sulfate per 10 liters of water. For chelates — according to instructions.
• Technique: Spray young and middle leaves thoroughly, especially on the underside. Repeat 2 times at intervals of 7 days. The effect is visible in a few days.
• Root feeding — prevention.
• Dosage: 10-20 grams of manganese sulfate per 10 liters of water. Water under the root once every 2-3 weeks on sandy or alkaline soils.

Important warning: Do not overdo it! Excess manganese is as dangerous as its deficiency. At manganese concentrations in the nutrient solution above 1-2 mg/L, toxicity can develop, manifested as old leaves covered with dark spots and growth inhibition (Jones, 2008). Signs of manganese excess often resemble iron deficiency. Therefore, always follow dosages, and it is better to under-feed than over-feed.

How to Recognize Copper Deficiency: Dark and Weak Leaves

Copper deficiency is not as easy to spot as, say, iron deficiency, because the symptoms are not as vivid. But they are very characteristic.

1. Dark green, almost blue leaves. This is a paradox: with copper deficiency, leaves become unnaturally dark, blue-green, often with a purple tint (Jones, 2008). The plant looks "overfed with nitrogen," but growth is stunted.

2. Curling and wilting of young leaves. Young leaflets at the top may curl into a tube, lose turgor, and even dry at the edges. Petioles become brittle and break easily (Ahatov, 2010).

3. Weak vascular system. Stems become soft, loose. The plant loses its ability to efficiently conduct water and nutrients.

4. Flower deformation and poor fruit set. Flowers may be underdeveloped, and fruit sets may drop. This is due to impaired hormone synthesis and tissue strength.

5. "Bleached" tips of old leaves. With severe deficiency, the tips of the oldest leaves seem to become discolored, almost white (Heuvelink et al., 2018).

Important: Symptoms of copper deficiency sometimes resemble iron deficiency, but with copper deficiency, leaves tend to darken rather than yellow, and growing points and flowers suffer first.

The Dual Role of Copper: Nutrition and Protection

Copper participates in the synthesis of lignin — a substance that makes cell walls strong and rigid. It is thanks to copper that tomato stems do not lodge, and the skin of fruits becomes elastic and resistant to cracking.

But the main "feature" of copper is its fungicidal properties. Copper ions suppress the development of many fungal and bacterial infections. Therefore, a plant supplied with copper resists diseases better, and treatments with copper-containing preparations (Bordeaux mixture, copper oxychloride) not only cure but also "feed" the tomato with this important element (Hochmuth & Sideman, 2023).

Causes of Copper Deficiency

1. Peat and organic soils. Copper binds very strongly to organic matter and becomes unavailable to plants. This is a common cause of deficiency on humus-rich soils (Jones, 2008).

2. Alkaline soils (pH > 7.0). Like many other micronutrients, copper transforms into insoluble forms.

3. Excess nitrogen and phosphorus. High doses of nitrogen and phosphorus aggravate copper deficiency.

4. Sandy, poor soils. On such soils, copper is simply scarce in available form.

How to Apply: A Prevention Strategy

Given the dual role of copper, the approach to its application should be comprehensive.

1. Preventive soil application. Especially important on peat and sandy soils before planting.

• What to use: Copper sulfate (copper sulfate, CuSO₄) — the most accessible form.
• Dosage: Usually 2-4 grams per 1 m² of soil as a solution or in dry form. Do not apply more — copper accumulates in the soil, and its excess is toxic.

2. Foliar feeding (by leaf). Used for rapid correction of deficiency and simultaneously for protection against diseases.

• What to use: Copper sulfate (0.05-0.1% solution, i.e., 5-10 grams per 10 liters of water) or specialized copper chelates. Spraying with a weak solution of Bordeaux mixture (1%) also works well.
• Technique: Spray all leaves thoroughly, especially young ones. The effect is visible in a few days.

3. Combination with fungicide treatments. Routine treatments with copper-containing preparations against late blight and other fungi automatically solve the problem of copper nutrition. This is convenient, but it is important not to exceed dosages to avoid burns and copper accumulation in fruits.

Caution: copper toxicity!

Copper is a "double-edged sword." Its excess is as dangerous as its deficiency. Signs of copper poisoning:

• Appearance of dark brown or purple spots on old leaves.
• Slowing of root growth.
• Symptoms resembling iron deficiency (copper blocks iron uptake) (Jones, 2008).

The critical level of copper content in tomato leaves is above 15-20 ppm (mg/kg dry weight). Therefore, never exceed recommended dosages and do not use copper-containing preparations more often than truly necessary.

How to Recognize Molybdenum Deficiency: Symptoms Resembling Nitrogen Starvation

This is the biggest trap for the gardener. Molybdenum deficiency masquerades as nitrogen deficiency, and the inexperienced gardener starts adding more nitrate, which only worsens the situation. Here are the key signs:

1. General yellowing (chlorosis) of old and middle leaves. As with nitrogen deficiency, it starts from the lower leaves. They become pale green or yellow (Ahatov, 2010).

2. "Speckling" and curling. Unlike pure nitrogen starvation, with molybdenum deficiency, characteristic speckling appears on leaves — small light spots between veins. Leaf edges may curl inward or upward (Heuvelink et al., 2018).

3. Spot necrosis. With severe deficiency, dry brown areas appear on the edges of leaves and at tips — tissues die (Jones, 2008).

4. Inhibition of flowering and fruit formation. Protein synthesis is disrupted, and the plant cannot form full-fledged flowers and fruit sets.

Important difference from nitrogen starvation: with nitrogen deficiency, leaves yellow evenly, without speckling. With molybdenum deficiency, yellowing has a spotted, "mosaic" character, and edges may curl (Hochmuth & Sideman, 2023).

Why Does Molybdenum Deficiency Occur? Enemy Number One — Acidic Soil.

Here is the main rule to remember once and for all: molybdenum is the only micronutrient whose availability decreases not in alkaline but in acidic conditions!

If iron, zinc, copper, and manganese are blocked at pH > 6.8, then molybdenum becomes unavailable at pH < 5.5 (Ahatov, 2010). In acidic soils, molybdenum binds strongly to iron and aluminum oxides and transforms into insoluble forms.

Therefore, the main causes of molybdenum deficiency are:

1. Acidic soils (pH < 5.5). This is the main and almost sole cause. On acidic peat bogs, podzolic soils, and sandy soils, the problem occurs regularly.

2. Excess sulfates (SO₄²⁻). Sulfur is an antagonist of molybdenum. High doses of ammonium sulfate or potassium sulfate can aggravate the deficiency (Jones, 2008).

3. High content of iron and aluminum in the soil. These elements bind molybdenum in acidic conditions.

How to Apply: The Importance of pH and Microdoses

Working with molybdenum requires special care — it is needed in very small amounts, but it is indispensable.

1. Correction of soil pH — long-term strategy. This is the most important step. If the soil pH is below 5.5, liming is necessary (apply dolomite flour, lime, or ash). Without this, you will fight deficiency forever. Raise pH to 6.0-6.5 — and molybdenum becomes available.

2. Foliar feeding (by leaf) — "first aid". This is the fastest way to deliver molybdenum to the plant, especially on acidic soils.

• What to use: Ammonium molybdate or sodium molybdate. These are the main available forms.
• Dosage: This is critically important! Molybdenum is needed in microscopic amounts. Usually 0.5-1 gram of ammonium molybdate per 10 liters of water (0.005-0.01% solution). Do not exceed the dosage!
• Technique: Spray leaves thoroughly, especially old and middle ones where symptoms appear. Repeat 1-2 times at intervals of 7-10 days. The effect is visible within a few days — leaves begin to turn green.

3. Root feeding. Used less often, mainly on soils with neutral reaction, as prevention.

• Dosage: 1-2 grams of ammonium molybdate per 10 liters of water. Water under the root once per season.

Caution: Molybdenum Deficiency and Nitrate Accumulation

This is an important point for health. If the plant lacks molybdenum, nitrates do not convert into amino acids and proteins. They accumulate in leaves and fruits as nitrates. High nitrate content in tomatoes is not only harmful to health but also a sign that the plant is "under-eating" molybdenum (Wien and Stützel, 2020).

Therefore, if you notice that with abundant nitrogen fertilization, tomatoes still look pale and weak, and fruits do not develop flavor, perhaps the problem is not the amount of nitrogen but the lack of molybdenum, which prevents that nitrogen from being absorbed.

Why Is Boron Needed, and Why Is It So Important to Combine It with Magnesium?

Boron is the element that manages the reproductive system of the tomato. Without boron:

• Pollen becomes sterile, and flowers fall off without setting fruit.
• Fruits become deformed, ribbed, hollow (so-called "hollow heart").
• Growing points die, stems become brittle and fragile (Jones, 2008).

Boron is also responsible for the transport of sugars from leaves to fruits. That is why its deficiency directly affects the flavor and sweetness of tomatoes (Heuvelink et al., 2018).

Magnesium, as we already know, is the core of chlorophyll. Without magnesium, the leaf cannot produce those same sugars that boron is supposed to deliver to the fruit. Therefore, the combination of magnesium and boron is a logical step: one creates the product, the other delivers it.

When and How to Apply Magbor?

Magbor is a preparation for critical growth phases, when the load on the plant is maximal.

1. Budding and early flowering period. This is the most important time for applying boron. Spraying with Magbor in this phase guarantees better pollination, fruit set, and reduces the risk of hollow fruit (Ahatov, 2010).

2. Period of active fruit growth. During this time, magnesium helps maintain high photosynthetic activity of leaves, and boron ensures the outflow of sugars into fruits, improving their flavor and color.

3. At the first signs of boron or magnesium deficiency. If you notice flowers dropping, fruit deformation, or interveinal chlorosis on leaves, Magbor can be a quick "first aid."

How to Use: Foliar Feeding Is a Priority

Magbor works best with foliar feeding (by leaf). Why?

• Boron in soil binds easily and becomes unavailable, especially on calcareous and sandy soils.
• Magnesium, although absorbed by roots, acts faster with foliar application.
• Spraying allows both elements to be delivered directly into tissues, bypassing competitive struggle in the soil.

Application Technique:

• Dosage: Strictly according to the product instructions. Usually, this is 10-20 grams of Magbor (or a similar fertilizer with MgO 16% and B 1-2%) per 10 liters of water.
• Time: Apply in cloudy weather or in the evening to avoid leaf burns.
• Frequency: 1-2 treatments at intervals of 7-10 days. The first — at the beginning of budding, the second — during mass flowering.

Important! Do not mix Magbor with phosphorus fertilizers (superphosphate, monopotassium phosphate) or calcium nitrate in the same tank — an insoluble precipitate forms (phosphate or calcium sulfate), and the effectiveness of the feeding is lost. It is better to apply treatments separately.

Special Case: Combined Application with Calcium

Boron and calcium are antagonists. Excess calcium blocks boron uptake. Therefore, if you regularly water tomatoes with calcium nitrate (to prevent blossom end rot), remember that the need for boron increases. In such a situation, Magbor becomes especially relevant because it supplies boron in an easily available form, bypassing competitive struggle with calcium in the soil (Jones, 2008).

Golden rule: Magbor is not a panacea but a tool for fine-tuning. Apply it in key growth phases, strictly observing dosages, and it will help you get not only abundant but also high-quality, tasty yields.

The Two Main Families of Micronutrient Forms

All forms of micronutrient fertilizers can be divided into two large groups:

1. Inorganic salts (sulfates, chlorides, nitrates).

• What they are: Magnesium sulfate (Epsom salt), iron sulfate (ferrous sulfate), zinc sulfate, manganese sulfate, copper sulfate (copper sulfate), ammonium or sodium molybdate.
• Pros: Cheapness, availability, time-tested forms.
• Cons: In soil and solution, metal ions quickly bind with other substances (phosphates, carbonates, organic acids) and precipitate, becoming unavailable to the plant. This process is especially intensified at pH > 6.5 (Jones, 2008). The plant can only absorb a "fresh" solution before the ion has time to bind.

2. Chelates (organic complexes).

• What they are: Micronutrients "packaged" in a protective organic molecule (chelate). The most common are chelates based on EDTA, DTPA, EDDHA.
• Pros: The metal ion is reliably protected from binding and oxidation. It remains in solution and available to the plant over a wide pH range (for DTPA and EDDHA — even at pH up to 8.0). It is absorbed almost 100%, acts quickly and effectively (Jones, 2008).
• Cons: More expensive than sulfates. They require precise dosage compliance, as excess chelates can block other elements.

The Main Selection Criterion: pH of Soil and Water

This is the decisive factor that should determine your strategy.

How to Use This Table in Practice

1. If you have acidic soil (pH 5.5-6.0): Sulfates (vitriols) will work effectively for iron, zinc, manganese, and copper, especially with root application. This is an economical option. For foliar feeding, both sulfates and chelates can be used.

2. If you have neutral or alkaline soil (pH > 6.5), or hard water: Sulfates in soil are almost ineffective. Your choice is chelates for iron, zinc, manganese, and copper. For foliar feeding, sulfates can be used, but the solution must be fresh, and leaves should be sprayed thoroughly on both sides.

3. For prevention (scheduled feeding): On acidic soils, sulfates can be used. On alkaline soils — only chelates or complex micronutrient fertilizers with chelated forms.

4. For treatment (obvious deficiency symptoms): Always use chelated forms for foliar feeding. They work faster and reliably deliver the element to the plant tissues.

Important Nuances

• Magnesium and molybdenum are exceptions to the rules. Magnesium in sulfate form works well everywhere. Molybdenum is the only micronutrient that becomes less available in acidic soils, so at pH < 5.5, first lime the soil, and then apply molybdate.
• Complex fertilizers with micronutrients. Many manufacturers offer ready-made "NPK + micro" mixtures. Check the form of the micronutrients. If it says "chelated forms" or "EDTA" — it is a quality product. If just "sulfates" — be prepared that some elements will bind in the soil.
• Compatibility when mixing. Remember the golden rule: do not mix sulfates (especially magnesium sulfate) and chelates with phosphorus fertilizers and calcium (calcium nitrate) in the same tank — a precipitate forms that clogs nozzles and makes the feeding useless (Hochmuth & Sideman, 2023). Use separate tanks or apply feeds separately.

Mistake #1. Treatment Instead of Prevention

What it is: The gardener waits for obvious deficiency symptoms (yellow leaves, spots, deformation) and only then grabs the sprayer.

Why it is bad: Micronutrients are not medicines but building blocks for enzymes and hormones. When a symptom is already visible, the plant has already lost precious time and part of the harvest. Iron deficiency at the top means growth is already stunted; boron deficiency means some flowers have already dropped irrevocably (Jones, 2008; Heuvelink et al., 2018).

How to do it right: Micronutrients are a planned adjustment. Apply them preventively in key growth phases:

• Before flowering: Boron, zinc, molybdenum for good fruit set.
• During fruit growth: Magnesium, iron, manganese, copper for powerful photosynthesis and leaf health.
• eventive foliar feeding with complex chelates 1-2 times a month is the best strategy.

Mistake #2. Working "By Eye" and Exceeding Dosages

What it is: The thought "more is better" is deadly for micronutrients. The gardener adds a "pinch" of copper sulfate or "a little" of ammonium molybdate, thinking it is safe.

Why it is bad: The difference between deficiency and toxicity for micronutrients is measured in milligrams (Jones, 2008). Excess copper or zinc is no less dangerous than their deficiency. It blocks iron uptake, causes root and leaf burns, and fixing this is much harder than replenishing a deficiency (Ahatov, 2010).

How to do it right: Use accurate scales (kitchen or pharmacy) and strictly follow the dosages in the instructions. For molybdenum and boron, this is critically important. No "by eye"! If the instructions say 1 g per 10 liters, then exactly 1 gram.

Mistake #3. Ignoring Soil and Water pH

What it is: Applying iron sulfate or zinc sulfate to alkaline soil (pH > 7.0) in hopes of curing chlorosis.

Why it is bad: In alkaline conditions, ions of iron, zinc, manganese, and copper instantly bind and precipitate as insoluble compounds. You pour fertilizer, but the roots do not see it. This is a waste of money and time (Jones, 2008). For molybdenum, the situation is reversed — it does not work in acidic soils (pH < 5.5).

How to do it right: Before buying fertilizer, measure the pH of your soil (or irrigation water if you are on hydroponics or in pots).

• pH > 6.8: Use only chelated forms (Fe-DTPA, Fe-EDDHA, chelates of Zn, Mn, Cu). For molybdenum, no problem.
• pH < 5.5: First, apply liming (dolomite flour, ash) to raise pH to 6.0-6.5. Without this, molybdenum will be unavailable.
• pH 6.0-6.5: Sulfates (vitriols) will work well, but chelates are still more effective and safer.

Mistake #4. Incorrect Mixing of Preparations

What it is: Mixing everything together in one tank (or bucket): magnesium sulfate + calcium nitrate, iron chelate + superphosphate.

Why it is bad: Chemistry is an exact science. Magnesium and calcium react with sulfates and phosphates to form insoluble salts (calcium sulfate — gypsum, phosphates). This precipitate is not only useless for the plant but can also clog sprayer nozzles (Hochmuth & Sideman, 2023).

How to do it right: Remember the "golden triangle of incompatibility":

• Calcium (calcium nitrate) — DO NOT mix with sulfates (magnesium, potassium, ammonium) and with phosphates (superphosphate, monopotassium phosphate).
• Iron (chelate) — DO NOT mix with phosphorus fertilizers.
• Boron — compatible with almost everything except alkaline solutions (lime, ash).
• Rule:** Prepare tank mixtures only if you are sure of compatibility. In most cases, for an amateur, it is safer to apply micronutrients separately from macronutrients or use ready-made complex fertilizers where compatibility has already been verified by the manufacturer.

Mistake #5. Confusion in Diagnosis

What it is: The gardener sees yellow leaves and decides it is nitrogen deficiency and sprinkles nitrate. Or sees interveinal yellowing at the top and treats with magnesium.

Why it is bad: As we have already discussed, symptoms of different deficiencies are similar but have important differences:

• Old lower leaves → look at magnesium (interveinal yellowing) or potassium (marginal burn).
• Young upper leaves → look at iron (bright vein network) or manganese (spots on a pale background), zinc (small leaves and rosetting).
• Problems with fruit set and flowers → look at boron.

How to do it right: Before grabbing fertilizer, conduct an "investigation": which leaves are affected (old or young), what does the damage look like (between veins, at edges, spots), and what growth phase is the plant in. Use our symptom descriptions from previous chapters. Only after confirming the diagnosis, apply targeted feeding.

Mistake #6. Focus Only on Root Feeding

What it is: The gardener waters with micronutrients under the root and wonders why there is no effect.

Why it is bad: In soil, micronutrients (especially iron, zinc, copper) quickly bind. Root feeding is a slow and not always effective strategy, especially on alkaline soils (Jones, 2008).

How to do it right: Foliar feeding (by leaf) is a priority for micronutrients. Spraying delivers elements directly into tissues, bypassing soil "traps." For iron, boron, zinc, and manganese, this is the main method of fast and reliable help. Use root feeding as prevention on acidic soils or for magnesium (magnesium sulfate), which is well absorbed by roots.

To summarize the main idea of the entire cycle:

Micronutrients are not a "supplement" to the harvest but a system of precise tuning. Working with them requires attention to detail: balance between elements, soil acidity, fertilizer forms, and plant growth phases. But it is this fine work that distinguishes a simply good harvest from an outstanding one: tasty, aromatic, healthy, and shelf-stable fruits that please the eye and the palate.

Remember: your task is not to feed the plant "more" but to help it unlock its genetic potential through competent and balanced care.