Growing Tomatoes in Protected Cultivation

2.1. Disinfection: Starting with a Clean Slate

A greenhouse is a closed ecosystem where pathogens, if left unchecked, can multiply rapidly. Therefore, the main goal of preparation is to start the season with a minimal number of pathogens and pests. Treatment is best carried out in the fall, after harvest, and repeated in spring, a few weeks before planting the seedlings.

Cleaning: Remove all plant debris – stems, leaves, roots, fallen fruits. They are an ideal environment for overwintering fungal spores, bacteria, and pest eggs (Nonnecke, 1989). Burn them or remove them from the site.

Washing: Thoroughly wash all interior surfaces: glass or polycarbonate, frames, shelving, equipment. Use a soapy solution or a solution of laundry soap. This will wash away dirt and the bulk of microorganisms (Gavrish, 2005).

Disinfection: This is the most important step. The choice of method depends on your capabilities.

• Sulfur bombs (fumigation): An effective method for controlling fungi, bacteria, mites, and insects. Close all vents and cracks, ignite the bomb, and leave the greenhouse for 1-2 days. Important: this method can be harmful to metal parts, so ensure they are protected or choose other methods for greenhouses with galvanized frames (Jones, 2008).
• Spraying with disinfectant solutions: Treat all surfaces with a 1-2% solution of copper sulfate or Bordeaux mixture. This is excellent prevention against late blight and other fungal diseases. You can also use a bleach solution (400 g per 10 liters of water), let it stand for 2-4 hours, and then spray the structure, using 1 liter of solution per 1 m² of surface (Gavrish, 2005).
• Biological method: In the fall, after cleaning, you can sow the greenhouse with green manures (mustard, phacelia) and incorporate them into the soil. This improves and enriches the soil.

2.2. Soil: A Healthy Foundation

Tomatoes need fertile, loose, and well-drained soil with a pH in the range of 6.0-6.8 (Nonnecke, 1989). In a greenhouse, soil depletes faster, so its preparation is given special attention.

Replacing the top layer: It is recommended to replace the top layer of soil (5-8 cm) annually with fresh soil. This reduces the infectious load (Gavrish, 2005).

Improving structure: Add well-decomposed compost or humus (5-8 kg per 1 m²) to improve structure and fertility. If the soil is heavy, clayey, add coarse river sand (1 bucket per m²) for better drainage.

Disinfection (if necessary): If the soil is infected with diseases, you can use one of the following methods:

• Steaming: A more labor-intensive method, but environmentally friendly.
• Biopreparations: Applying preparations based on Trichoderma (e.g., Trichoderma viride) a few weeks before planting helps suppress pathogen development (Ahatov, 2010).

Fertilizer Application: This point is closely related to fertilizing. Basic fertilizers (phosphorus and potassium) are best applied in the fall during digging. Nitrogen fertilizers are left for liquid fertilizing during the growth period to avoid excessive "luxuriance" of plants (Gavrish, 2005).

2.3. Trellis: Vertical Support

Tomatoes in a greenhouse, especially indeterminate varieties, need a reliable support. A proper trellis is your working tool for shaping the plant, providing ventilation, and ensuring light access to all parts.

1. Structure: At a height of 2.0-2.5 meters above the beds, a strong galvanized wire is stretched along each row.

2. Tying: To this wire, twine (or special tape) is tied for each plant. The twine is lowered down and attached with a loose loop to the base of the stem. This allows you to regularly twist the stem around the twine as it grows, guiding it upwards (Gavrish, 2005).

3. Why is this important? Such a system allows efficient use of vertical space, simplifies plant care (removing suckers, leaves), improves ventilation and lighting, and will later allow "lowering" the plants to extend the growing season (more details in the "Formation" chapter).

2.4. Ventilation: The Respiratory System for Your Greenhouse

In the "Specifics" chapter, we already discussed the critical importance of ventilation. In a greenhouse, it is needed not only to lower temperature but also to control humidity and supply fresh CO₂. It is ventilation and a well-designed irrigation system that form the basis for disease prevention.

1. Types of ventilation:

• Natural ventilation: Vents and doors. Warm air rises and exits through the upper vents, while cool air is drawn in through the lower ones. For effective ventilation, the area of opening vents should be at least 15-25% of the floor area (Jones, 2008).
• Forced ventilation: Fans (exhaust or for air circulation). They are necessary for actively mixing the air, especially on hot days. It is important that fans ensure air movement through and within the plant canopy, not just above them. For this purpose, circulation fans (HAF fans) are used, which create a horizontal air flow in the plant zone (Jones, 2008).
• Practical steps:
• Check functionality: Make sure all vents open and close, and fans are working. It is advisable to install thermostats for automatic fan activation when the set temperature is exceeded.
• Don't wait until it gets hot: Start ventilating early in the morning when the temperature inside begins to rise. This allows you to release excess night moisture and avoid a sharp temperature spike.
• Use shading: Direct sunlight in southern regions can overheat the greenhouse. Use a special shading net or apply diluted chalk to the glass. Even slight shading can significantly reduce temperature and, consequently, the load on the ventilation system (Ahatov, 2010).

Preparing the greenhouse is a serious stage that may seem labor-intensive, but it pays off handsomely. A healthy start is the key to a long and productive season. In the next chapter, we will discuss how to properly transplant seedlings into the prepared space.

3.1. Planting Scheme: More is Not Always Better

In a greenhouse, we have limited space, and every square meter must work at maximum output. However, overcrowding is one of the most common and dangerous mistakes. Too dense planting leads to:

• Competition for light: plants stretch, internodes elongate, fruit set decreases (Gavrish, 2005).
• Poor ventilation: air stagnates, humidity rises, triggering the development of fungal diseases (late blight, gray mold, leaf mold) (Jones, 2008).
• Difficult maintenance: hard to tie, remove suckers, and carry out treatments.

The main principle of choosing a scheme is to provide each plant with sufficient feeding area and light.

The standard and most effective scheme for greenhouses is the strip planting scheme. Beds are formed along the length of the greenhouse (from north to south for better lighting). In each bed, plants are planted in two rows, which are spaced 50–60 cm apart. Between adjacent strips (beds), a wide passage is left – 80–100 cm (Gavrish, 2005). This passage is needed for free movement, care, and, most importantly, for air circulation.

The distance in the row between plants is the main adjustable parameter. It depends on the growth type and vigor of the variety:

• For indeterminate (tall) varieties, which we grow in one stem and which bear fruit for a long time, the distance in the row should be 35–45 cm. This provides them with a feeding area of about 0.4 m² per plant (Jones, 2008).
• For determinate and semi-determinate varieties, which have limited growth and are more compact, the distance can be reduced to 25–35 cm. However, it is important to remember that determinate varieties, although shorter, often have a denser bush, so they cannot be planted too close to each other.

Why exactly this way? With this scheme, plants receive maximum light, and air circulates freely between rows and within the plants, which is critically important for tomato health (Nonnecke, 1989).

3.2. Planting Density: Calculation for Your Greenhouse

Planting density is the number of plants per square meter. It is directly related to the chosen scheme.

• For tall indeterminate varieties, the recommended density is 2.2–2.8 plants per 1 m². With a strip scheme (80+50)×(35–40) cm, this gives about 2.5–2.8 plants/m² (Gavrish, 2005).
• For determinate varieties, especially for a short cycle, the density can be higher – 3.0–4.0 plants per 1 m². With a scheme (70+50)×(25–30) cm, we get about 3.5–4 plants/m².

However, these figures are guidelines. The main criterion is the quality of the seedlings and the light level in your greenhouse. In low light conditions (cloudy region, shaded area), the density should be reduced so that each plant gets more light. In southern, sunny regions, the density can be slightly increased.

3.3. Planting Technique: Key to a Quick Start

The procedure of transplanting in a greenhouse is not complicated, but there are several important nuances.

1. Preparing holes: Make holes large enough to freely accommodate the root ball of the seedling. If you are transplanting overgrown seedlings, they can be planted tilted, laying part of the stem in a furrow and covering it with soil. This stimulates the formation of additional roots (Gavrish, 2005).

2. Planting depth: Optimally, bury the plant down to the first true leaves. This promotes the development of a powerful root system. However, do not plant too deep if the soil has not yet warmed up – this may slow growth (Gavrish, 2005).

3. Watering: Immediately after planting, water the holes abundantly with warm water (about 1–1.5 liters per plant). This ensures good contact between roots and soil and relieves stress.

4. Shading: In the first 2–3 days, especially in sunny weather, it is advisable to shade the seedlings (with paper, non-woven material). This helps them withstand transplanting more easily while the root system recovers (Ahatov, 2010).

A week after transplanting, when the plants start to grow, you can begin the first ties and start formation – we will talk about this in the following chapters.

4.1. Temperature: The Main Regulator of Development

Temperature is the most powerful lever for controlling tomato development. It affects everything: from seed germination speed to fruit color and taste. Remember the main rule: temperature must change depending on light levels and the plant's developmental stage.

Optimal values:

• Daytime in sunny weather: 22–25 °C. In cloudy weather: 20–22 °C (Gavrish, 2005; Jones, 2008).
• Nighttime: 16–18 °C. It is critically important that the night temperature is at least 5–7 °C lower than the daytime temperature. This is the so-called DIF effect (difference between day and night temperature). Lowering night temperatures slows respiration and promotes the accumulation of assimilates in the fruits, not in the foliage. This prevents "luxuriance" — excessive leaf growth at the expense of fruiting (Wien & Stützel, 2020; Jones, 2008).

Critical thresholds:

• Below 10–12 °C: Growth stops, pollen loses viability, flowers drop (Jones, 2008). Prolonged exposure to low temperatures (below 15 °C) makes plants vulnerable to gray mold (Ahatov, 2010).
• Above 30–32 °C: Pollen becomes sterile, ovaries do not form. Flowers and young ovaries drop. High temperature combined with low humidity sharply worsens pollination (Jones, 2008; Nonnecke, 1989).
• Above 35 °C: Photosynthesis slows down, fruit development stops.

Practical recommendations:

• In spring and autumn, the main task is to retain night heat. Use double covering (inner layer of film or non-woven material), warm beds.
• In summer, the main enemy is overheating. Here, ventilation (see below) and shading come to the rescue. Even light shading reduces the temperature in the greenhouse by a few degrees.
• Use thermometers. It is better to have two: one at a height of 1 m above the bed level (for air control), the second for controlling soil temperature. The optimal soil temperature for tomatoes is 20–25 °C. When soil temperature is below 14 °C, roots stop absorbing nutrients (Gavrish, 2005).

Optimal microclimate profile for tomato.

4.2. Air Humidity and Ventilation: Two Inseparable Concepts

For tomatoes, the optimal relative air humidity is 60–70% (Gavrish, 2005). In a greenhouse, humidity often skyrockets, especially at night and in the morning. Excessive humidity is the main companion of diseases and the enemy of pollination.

Why ventilation is important:

1. Humidity reduction: High humidity leads to condensation on leaves and fruits, creating ideal conditions for fungal development (late blight, gray mold, leaf mold) (Ahatov, 2010).

2. Temperature reduction: Ventilation is the simplest and most effective way to cool the greenhouse on hot days.

3. Ensuring CO₂ supply: In a closed greenhouse on a sunny day, the carbon dioxide concentration can quickly drop below 200 ppm, halting photosynthesis. The influx of fresh air replenishes CO₂ reserves (Jones, 2008).

Practical recommendations:

• Ventilation is a system, not a one-time action. Start ventilating the greenhouse in the morning, as soon as the inside temperature begins to exceed the outside. This allows you to "push out" the humid air.
• Open not only doors but also upper vents. Warm air rises, and its outflow through the upper openings creates draft that draws out moisture and heat.
• On hot days, use fans. Regular household fans directed along the rows mix the air well, preventing stagnation. Circulation fans (HAF fans) are more effective, creating a horizontal air flow in the plant zone (Jones, 2008).
• Watch for dew. If you see water droplets on leaves and fruits in the morning — it's an alarm signal. It means it was too humid at night. Increase ventilation.

4.3. Carbon Dioxide (CO₂): Aerial Fertilizer

Tomato is a C3 plant, which means it is very responsive to increased carbon dioxide concentration in the air. In open air, the CO₂ concentration is about 400 ppm. In a greenhouse on a sunny day, it can drop to 200 ppm, severely limiting photosynthesis (Jones, 2008).

Effect: Increasing CO₂ concentration to 800–1000 ppm during sunny hours can increase yields by 20–40% (Wien & Stützel, 2020). Tomato actively absorbs CO₂ only in good light, so enrichment is useless in cloudy weather.

Enrichment methods for amateurs:

1. Natural: Organic fermentation. Place a barrel of water in the greenhouse and add fresh manure, grass, or special compost accelerators. During fermentation, CO₂ is released (Ahatov, 2010).

2. Gas combustion: A more complex and dangerous method (requires good ventilation and control over combustion products). Not recommended for amateurs.

3. Commercial CO₂ generators: Expensive equipment, not always justifiable for small greenhouses.

Important: When increasing CO₂, the temperature must also be raised by 2–3 °C, as at high CO₂, the temperature optimum for photosynthesis increases (Jones, 2008).

4.4. Lighting and Shading: Balancing Light and Overheating

Light is the energy source for photosynthesis. Tomatoes are light-loving and need plenty of light. In a greenhouse, we cannot control the amount of sunlight, but we can manage its distribution and avoid overheating.

Problem: Direct sunlight can heat the greenhouse to critical temperatures and also cause "sunscald" on fruits (Ahatov, 2010).

Solution:

• Shading nets. This is the ideal tool. A net with 40-50% density diffuses sunlight, lowering the temperature by 5–7 °C, while most photosynthetically active radiation (PAR) reaches the leaves. It is better to place the net outside the greenhouse – so it won't heat the air inside (Jones, 2008).
• Whitewashing. In older greenhouses, glass can be whitewashed with a chalk solution. This is a temporary but very budget-friendly shading method.
• Timing of shading. Start shading the greenhouse when the temperature rises above 28–30 °C. Remove the net in the evening so plants get more light in the morning and evening hours.

In the next chapter, we will move on to another vitally important aspect — irrigation and its specifics in protected cultivation.

5.1. Why Irrigation in a Greenhouse is an Art

• No natural precipitation: Tomato roots are entirely dependent on your irrigation. Miss a watering on a hot day – plants wilt and drop flowers. Overwater – roots rot, and late blight starts.
• High air humidity: In an enclosed space, water evaporated from the soil and leaves remains inside the greenhouse. This increases air humidity, which, as we already know, provokes diseases and worsens pollination. Irrigation and ventilation are two interconnected processes. Irrigation must be planned so as not to create excessive air humidity (Ahatov, 2010).
• Salt accumulation: In a greenhouse, there is no rain to wash away excess salts from the soil. With frequent fertilizer application (especially with irrigation), excess salts can accumulate in the soil or substrate, inhibiting the root system and deteriorating fruit taste.

5.2. Drip Irrigation: Your Main Tool

For a greenhouse, drip irrigation is not a luxury, but a necessity. It is the most efficient and controllable system.

How it works: Water (or fertilizer solution) is supplied through a system of tubes and drippers directly to the roots of each plant, wetting only the root zone.

Advantages:

1. Leaves stay dry: Water does not get on leaves and stems, sharply reducing the risk of fungal diseases (late blight, gray mold, leaf mold) (Jones, 2008).

2. Water saving: Water is used only as intended, without losses from surface evaporation.

3. Precise dosing: You can accurately control how much water and fertilizer each plant receives. This is especially important when using fertigation (see the "Fertilizing" chapter).

4. Convenience and time saving: The system works automatically; you don't need to carry watering cans or hoses.

How to set up drip irrigation: In the greenhouse, a main pipe (PVC or polyethylene) is laid along each row, from which a drip tape or dripper goes to each plant. The distance between drippers should match the distance between plants in the row. You can start with a simple purchased system that assembles like a construction set.

5.3. When and How Often to Water?

This depends on the growth phase, weather, and soil type.

Growth phase:

• After transplanting: Water moderately for the first week to avoid excess moisture against the background of still unheated soil. This stimulates the active growth of the root system in depth (Gavrish, 2005).
• During flowering and fruit set: Reduce watering. Optimal soil moisture is 70–75% of full field capacity. This restrains excessive vegetative growth ("luxuriance") and promotes better fruit set (Jones, 2008).
• During fruit growth and ripening: The need for water is maximum. Maintain soil moisture at 80–85% of full field capacity. Lack of moisture during this period will lead to wilting and cessation of fruit growth (Nonnecke, 1989).

Time of day:

• The best time for watering is morning. Morning watering allows plants to get water before the heat sets in. In addition, the soil surface has time to aerate by evening, reducing nighttime air humidity.
• Avoid evening watering. Watering in the evening, especially in cold weather, creates excess moisture in the soil and air for the entire night. This is a direct path to the development of fungal diseases and root rot (Ahatov, 2010).
• Daytime watering is permissible if it is not a sprinkler system. Sprinkling on a hot day can cause leaf burns.

Watering rate: Abundantly, but infrequently. It is better to water less often (1–2 times a week depending on the weather), but with a larger volume of water, to soak the entire root zone (up to 20–30 cm). Frequent shallow watering causes roots to grow near the surface, making plants susceptible to drought (Jones, 2008). The watering rate in a greenhouse for an adult fruiting plant can reach 2–4 liters per day in hot weather.

5.4. Water Quality: What You Need to Know

Water for irrigation should be warm (20–25 °C). Watering with cold water causes stress in plants, roots stop absorbing nutrients, and it provokes diseases such as blossom-end rot (Jones, 2008).

Signs of overwatering: Constantly wet soil, soil acidification, yellowing and wilting of lower leaves, presence of moss on the soil surface.

Signs of lack of water: Loss of turgor (leaves droop), on a hot day plants may wilt slightly, which is normal, but if turgor does not recover by evening — it's a signal for urgent watering.

5.5. Leaching Irrigations: Combating Salinization

With regular application of mineral fertilizers, ballast salts (especially sodium and chlorine) accumulate in the soil. This phenomenon is called salinization. It inhibits the root system; the plant absorbs water and nutrition worse; fruits become small and tasteless.

What to do? Periodically (about once a month) carry out leaching irrigations. Give the soil a large volume of water (2–3 times more than usual) so that it percolates deeply and washes excess salts below the root zone. Important: do this when the soil is sufficiently warm so as not to chill the roots. After a leaching irrigation, be sure to let the soil dry before the next watering (Jones, 2008; Gavrish, 2005).

Remember: proper irrigation in a greenhouse is not just moistening the soil; it is managing air humidity, nutrition, and the health of your plants. In the next chapter, we will explain how to combine irrigation with fertilizing using the fertigation method.

6.1. Why Fertilizing in a Greenhouse is a Special Approach

In open ground, plants have a larger feeding area and can extract some elements from deeper soil layers. In a greenhouse, especially when using a limited volume of soil or substrate, this reserve is limited. Additionally, intensive fruiting of tomatoes requires a huge amount of nutrients.

In protected cultivation, we cannot simply "charge" the soil with fertilizers for the entire season. We must constantly and accurately dose nutrition according to the plant's growth phase. This allows us to:

1. Manage the balance between growth and fruiting. Excess nitrogen — and the plant "luxuriates," growing foliage at the expense of fruits. Potassium deficiency — and fruits become smaller, lose taste and color.

2. Avoid salt accumulation and soil contamination. By applying fertilizers precisely according to need, we reduce the risk of salinization.

3. Maximize yield and quality. A tomato receiving balanced nutrition at each stage yields more and better-quality fruits.

6.2. Fertigation: Smart Irrigation + Smart Nutrition

Fertigation is a method of applying fertilizers along with irrigation water. In a greenhouse, this is the most effective way to feed, especially with drip irrigation (Jones, 2008).

How it works:

1. Stock solution: You prepare a concentrated fertilizer solution in a separate container (tank).

2. Injector (doser): This is a device connected to the irrigation system. It doses a small amount of the stock solution into the water stream, creating a working solution of the desired concentration (Jones, 2008; Gavrish, 2005).

3. Delivery to roots: This working solution reaches the roots of each plant through the drippers.

Advantages of fertigation:

• High precision: You know exactly how much and which elements each plant receives.
• Efficiency: Nutrients are delivered directly to the root zone and are absorbed as quickly as possible.
• Economy: Fertilizers are used only as intended, without losses.
• Automation: The process can be automated by setting the desired watering and feeding program.

6.3. What You Need to Know About Tomato Nutrition

Tomato is a crop with high nutritional requirements. But it is important not just to give it a lot, but to give the right balance of elements at the right time (Nonnecke, 1989).

Main macronutrients and their role:

1. Nitrogen (N): Building material for leaves and stems.

• Demand: Maximum during active growth, before flowering begins.
• Mistake: Excess nitrogen during flowering and fruiting leads to "luxuriance" — powerful foliage and poor fruit set. Fruits become watery, with low sugar content (Jones, 2008).
• Deficiency symptoms: Small pale green leaves, general stunting.
• Excess symptoms: Dark green, "fatty" leaves, delayed flowering.

2. Potassium (K): The element of fruit quality. Responsible for size, color, shelf life, sweetness, and disease resistance (Jones, 2008).

• Demand: Maximum during fruit formation and ripening. Tomato consumes more potassium than nitrogen (Nonnecke, 1989; Wien & Stützel, 2020). The K:N ratio during fruiting should be about 2.5:1.
• Deficiency symptoms: Leaf margin burn (edges turn brown, dry out), uneven fruit ripening (green "shoulders").

3. Phosphorus (P): Responsible for root development, flowering, and fruit set (Nonnecke, 1989).

• Demand: Moderate, but constant. Especially important at the beginning of the growing season.
• Deficiency symptoms: Slowed growth, purple tint on the underside of leaves and stems. Often, phosphorus deficiency occurs not because of its absence in the soil, but because of cold soil, when roots cannot absorb it.

4. Calcium (Ca) and Magnesium (Mg):

• Calcium: Critically important for preventing blossom-end rot in fruits (see the "Diseases" chapter). Provides cell wall strength (Jones, 2008).
• Magnesium: Part of the chlorophyll molecule. Its deficiency manifests as interveinal chlorosis on older leaves (Gavrish, 2005).

6.4. How to Choose and Prepare Fertilizers

For fertigation, fully water-soluble fertilizers are used. These can be:

1. Ready-made complex fertilizers (e.g., "Kemira," "Master," "Crystallon"). They are produced specifically for different crops and growth phases (for seedlings, for flowering, for fruiting). This is the simplest and most reliable option for beginners, as the manufacturer has already balanced the elements.

2. Individual salts: Experienced gardeners can independently mix fertilizers using, for example, calcium nitrate (source of nitrogen and calcium), potassium nitrate (source of nitrogen and potassium), monopotassium phosphate (source of phosphorus and potassium), and magnesium sulfate (source of magnesium and sulfur). This gives greater flexibility but requires precise calculations (Jones, 2008).

Important: Calcium nitrate and other salts cannot be mixed in one stock solution, as they can react and form an insoluble precipitate (gypsum, calcium phosphate). Prepare two separate stock solutions, which are supplied to the system through different injectors (Jones, 2008; Gavrish, 2005).

6.5. Practical Fertilizing Schedule

General rule: The concentration of the working fertilizer solution (measured by EC — electrical conductivity) should be higher during fruiting and lower during growth. For tomatoes, the optimal EC of the working solution is 1.8–2.5 mS/cm (Jones, 2008).

Approximate fertilizing schedule (for indeterminate varieties):

NPK demand by phase.

Important: This scheme is only a guideline. Specific dosages depend on your soil type, water quality, and variety. The main control tool is observation of the plant (leaf color, fruit condition) and, ideally, soil and leaf analysis. If lower leaves turn yellow and edges curl — it's a signal of potassium or magnesium deficiency. If they turn dark and look "fatty" — an excess of nitrogen.

6.6. Salt Accumulation and Leaching Irrigations

As mentioned in the "Irrigation" chapter, with constant fertilizer application, ballast salts can accumulate in the soil or substrate. This is especially relevant when using hard water. Signs of salinization: white crust on the soil surface, leaf margin burn, growth cessation.

What to do? Periodically (every 2–3 weeks) carry out a leaching irrigation with clean water in a volume 2–3 times the usual amount. This washes excess salts from the root zone (Jones, 2008). After a leaching irrigation, be sure to let the soil dry and then resume fertigation as usual.

In the next chapter, we will move on to plant formation — the art of managing bush architecture for maximum yield.

7.1. Why Formation in a Greenhouse is Mandatory?

In a greenhouse, we mainly deal with indeterminate (tall) varieties and hybrids. Their growth potential is practically unlimited: under favorable conditions, they can reach heights of 3-5 meters or more (Jones, 2008). If such a plant is not formed, it will turn into impenetrable jungle where:

1. Fruits will become smaller and lose quality due to competition for nutrition.

2. Overcrowding will lead to lack of light and ventilation, provoking diseases.

3. Working with the plant (watering, tying, treating) will become practically impossible.

4. Inefficient space use: most of the energy will go into growing useless foliage, not fruits.

The main goal of formation in a greenhouse is to transform a tall tomato into one powerful, continuously fruiting "vine" (Nonnecke, 1989). This allows you to keep the plant vertical, direct all its forces to fruit development, and harvest for many months.

7.2. One Stem — The Golden Standard of the Greenhouse

For greenhouse tall (indeterminate) tomatoes, the most effective and common method is formation into one stem. This means that only the central shoot (main stem) is left on the plant. All other shoots growing from leaf axils (the so-called suckers) are regularly removed (Gavrish, 2005; Jones, 2008).

Why it works?

• Maximum yield: All the plant's energy is directed to the growth and nutrition of the central stem and the fruit clusters forming on it.
• Better lighting and ventilation: One stem with leaves occupies a minimum of space, does not shade neighbors, and is well ventilated.
• Ease of care: Easy to tie, treat, and harvest.
• Long fruiting period: A plant grown in one stem does not waste energy on developing useless foliage and can bear fruit for months.

7.3. Removing Suckers (Suckering): Regular "Pruning"

Suckers are side shoots that grow from leaf axils (the angle between the stem and the leaf petiole) (Gavrish, 2005). If not removed, they will turn into new stems that will compete with the main one for light and nutrition.

Rules for effective suckering:

• Regularity: Suckers should be removed weekly, and during periods of active growth, twice a week. They must not be allowed to overgrow. The smaller the sucker, the easier and less painful it is to remove (Jones, 2008). The optimal length for removal is 3–5 cm.
• Technique: Suckers are best snapped off (pinched) with fingers, leaving no stubs. To do this, take the sucker with two fingers and with a sharp movement bend it to the side. Do this in the morning when plants are most turgid (filled with moisture) and suckers break off easily (Jones, 2008).
• Main principle: Leave 1–2 leaves above the topmost flower cluster. They are needed to feed this cluster and protect it from sunburn.
• Special case — determinate varieties: If you are growing determinate varieties (with limited growth), they can be formed into 1 stem, but you need to leave a reserve sucker. This is because in such varieties, stem growth ends with a flower cluster. If you remove all suckers, the plant will stop growing. A reserve sucker (under the topmost cluster) is left in case the main stem "terminates," and then this sucker becomes a new continuation (Gavrish, 2005). However, for simplicity, indeterminate varieties that do not require such a complex scheme are more often used in greenhouses.

7.4. Plant Lowering (Laying Down the Stem): Extending the Bush's Life

When an indeterminate tomato reaches the top of the trellis (2–2.5 m), its growth does not stop. To continue harvesting, the plant needs to be allowed to grow further. For this, the technique of lowering (laying down) the stem is used (Jones, 2008; Gavrish, 2005).

How it works:

1. When the plant reaches the top of the trellis, it begins to be gradually, at intervals of 1–2 weeks, lowered down. To do this, loosen the twine and lay the lower part of the stem on the ground, along the bed surface.

2. Before lowering, remove all leaves and fruiting clusters below the point that will lie on the ground. The stem should retain only the upper, actively growing parts.

3. Lay the stem on the ground in a circle or along the row, carefully guiding it. It is important that it does not bend or break.

4. The plant continues to grow upwards, and its tip reaches the trellis again. The cycle of "lowering-growth" repeats several times during the season.

Why is this needed?

• Extending plant life: Allows using the unlimited growth of indeterminate varieties to obtain a harvest for 6–8 months or more.
• Constant rejuvenation: By lowering the stem, we seem to move the growing point down, closer to the roots, and give the plant a second wind.
• Maximizing vertical space use: Allows keeping the active (fruiting) part of the plant at a height of 1.5–2 meters, where it is well lit and convenient for care.

7.5. Leaf Removal: Ventilation and Fruit Nutrition

This is another important element of formation that is often overlooked. Removing lower, old, and diseased leaves is not just a cosmetic procedure, but an important agronomic practice.

What and when to remove:

• Old, yellowed, and diseased leaves: Remove them as soon as they appear. This prevents the spread of diseases (Ahatov, 2010).
• Leaves touching the ground: They are the primary source of infection. Remove them too.
• Lower leaves that have already fruited: When fruits from the lower clusters have ripened and been harvested, the leaves under these clusters are no longer needed. They do not participate in photosynthesis but create shading and air stagnation. They are gradually, one by one, removed when the fruits on the corresponding cluster reach the size typical for the variety (e.g., 4–5 cm in diameter) (Jones, 2008).

Leaf removal scheme:

• As a rule, 2–3 lower leaves are removed weekly, as the lower clusters mature (Jones, 2008). The plant should retain about 18–20 healthy leaves. This is the optimal leaf-to-fruit ratio for good photosynthesis and fruit filling.

Why is leaf removal important?

1. Improves ventilation: Air circulates freely in the lower part of the stem, reducing humidity and the risk of fungal diseases.

2. Improves lighting for lower clusters: This promotes better coloring.

3. The plant spends less energy maintaining useless foliage: All nutrition is directed to the fruits.

Important: Remove leaves in dry weather, in the first half of the day, so that the cut sites have time to dry during the day and do not become "entry gates" for infection. Stems after removal should be clean, without stubs.

Formation is an art that requires attention and regularity. But it is precisely this that allows you to get in the greenhouse the very harvest we expect. In the next chapter, we will talk about how to help the tomato set fruit in protected cultivation conditions — about pollination.

8.1. Why Help is Needed in a Greenhouse?

Open flower truss of a small‑fruited tomato (grape type).

Truss with open yellow tomato flowers. Petals are reflexed, exposing the fused anther cone. Stems and pedicels are densely pubescent with glandular hairs.

Tomato is a self-pollinating plant. In its flower, male and female organs (stamens and pistil) are located close together. Under ideal conditions, pollen from the anthers should fall onto the stigma of the pistil. However, in a greenhouse, there are two main obstacles:

1. Lack of wind and pollinating insects. In nature, wind shakes the plants, and pollen falls out of the anthers. In a greenhouse, especially in calm weather, pollen remains inside the flower and does not reach the stigma (Jones, 2008).

2. High air humidity. When humidity exceeds 70–80%, pollen grains become heavy, stick together, and do not fall out. At low humidity (below 40–50%), pollen dries out and does not germinate on the stigma (Nonnecke, 1989; Gavrish, 2005).

Therefore, to guarantee fruit set, we need to artificially create conditions that stimulate pollen movement and its deposition on the stigma.

8.2. When and How to Help?

The simplest and most accessible method for the amateur gardener is mechanical shaking.

When: During mass flowering, in the morning hours (from 10 am to 1 pm). At this time, the air has already warmed up, humidity is relatively low, and pollen is most viable (Jones, 2008).

How often: 2–3 times a week.

Technique:

• Stem shaking: Lightly tap the trellis wire or the upper part of the stem with your fingers. This creates vibration that transfers to the flowers. Be careful not to damage the stems.
• Inflorescence shaking: Gently hold the flowering cluster by the peduncle and shake it slightly. This method is better if you are working with large-fruited varieties.
• Electric vibrator: A more effective method. You can purchase a special electric pollinator for tomatoes or use a small electric toothbrush. Turn on the vibrator and apply it for 2–3 seconds to the back of the flowering cluster (to the stem where the flowers sit). Do this in the morning when the flowers are "open" (Jones, 2008; Gavrish, 2005).

Important: After shaking, the air humidity in the greenhouse is slightly increased (e.g., by spraying the walkways with water). This helps the pollen germinate. The optimal humidity for pollen germination is 70–75% (Gavrish, 2005).

8.3. Bumblebees — Professional Helpers

For greenhouses, especially large ones (over 100 m²), the most effective and reliable pollination method is the use of bumblebees (Bombus terrestris) (Jones, 2008; Wien & Stützel, 2020). Bumblebees are ideal pollinators for tomatoes for several reasons:

1. They work in any weather: Unlike honeybees, bumblebees are active at lower temperatures (from +8 °C) and in cloudy weather.

2. They "buzz": Bumblebees produce vibrations of a specific frequency that cause pollen to fall out of the anthers. This is called "buzz pollination." This very vibration is the key to success (Wien & Stützel, 2020).

3. They are not aggressive and do not sting: Bumblebees used in greenhouses are docile and rarely sting if not disturbed.

4. Convenience: You purchase a special hive with a bumblebee colony (it contains a queen, workers, and food supply). The hive is placed in the greenhouse at a height of 0.5–1 meter, and the bumblebees find the flowers on their own. One hive lasts for 6–8 weeks. For 1000 m², 2–3 hives are needed (Jones, 2008; Gavrish, 2005).

How to tell if bumblebees are working?

• Marks on flowers: After a bumblebee visits, a brown spot (traces from mandibles) remains on the lower part of the flower. If you see such marks on 50–60% of the flowers in the greenhouse, pollination is proceeding normally. If less, you need to add more bumblebees (Jones, 2008).
• Activity: Observe the bumblebees. In sunny weather, they fly actively. If there are few, perhaps it is too hot in the greenhouse (above 35 °C) or too humid (above 90%).

Important: When using chemical plant protection products, the hive is removed from the greenhouse during treatment or covered (depending on the type of product). Bumblebees are very sensitive to pesticides (Jones, 2008).

8.4. Another Method — Hormonal Stimulation

This method is not pollination in the classical sense. Instead of pollen, special preparations based on gibberellins or auxins are used (e.g., "Ovary," "Tomaton"). These hormones stimulate ovary growth without fertilization (parthenocarpy) (Gavrish, 2005).

Advantages: Guarantees fruit set in unfavorable conditions (cold, heat, high humidity). Often used in early spring greenhouses when bumblebees are not yet active (Ahatov, 2010).

Disadvantages:

• Fruits often turn out hollow (seedless) and less tasty.
• Incorrect dosage can cause fruit deformation.
• Requires manual labor (spraying each flower).

Conclusion: For amateur and small greenhouses, the simplest and most environmentally friendly method is mechanical shaking, especially combined with maintaining optimal humidity and temperature. If the greenhouse is large or you want to minimize labor, invest in bumblebees. Hormonal preparations are a "last resort" option or for early harvests when other methods are ineffective.

In the next chapter, we will move on to plant protection — diseases and pests that are especially active precisely in greenhouse conditions.

9.1. Why are Diseases a Particular Problem in a Greenhouse?

In a greenhouse, there are three factors that make plants more vulnerable:

1. High air humidity. This is the main cause of most fungal diseases. Condensation on leaves and fruits is an ideal environment for the germination of spores of late blight, gray mold, and leaf mold (Ahatov, 2010; Jones, 2008). This is why ventilation is your main ally.

2. Lack of natural enemies. In open ground, pest numbers (aphids, whiteflies) are kept in check by ladybugs, green lacewings, parasitic wasps. In a greenhouse, these enemies are absent, and populations can grow exponentially.

3. Monoculture. If you grow tomatoes year after year in the same greenhouse, pathogens (Fusarium wilt, Verticillium wilt, bacterial canker) accumulate in the soil (Nonnecke, 1989).

The golden rule of the greenhouse: prevention is cheaper and more effective than cure. It is much easier to prevent a disease than to fight it once it has spread.

9.2. Prevention — The Foundation of Greenhouse Health

These simple rules should become a habit:

1. Follow crop rotation: Do not grow tomatoes in the same place for more than two years in a row. If this is not possible, replace the top layer of soil (5–10 cm) before each season (Gavrish, 2005).

2. Disinfect the greenhouse: Carry out disinfection of structures and soil in autumn and spring (see the "Greenhouse Preparation" chapter).

3. Use resistant varieties and hybrids: Modern hybrids (e.g., F1 with markings Tm, C, V, F, N) have genetic resistance to a number of diseases: tobacco mosaic virus (Tm), leaf mold (C), Verticillium wilt (V), Fusarium wilt (F), and nematodes (N) (Gavrish, 2005). This is the most reliable protection method.

4. Follow watering and ventilation regimes: Do not allow over-moistening of soil and air. Water only in the morning and only at the root, regularly ventilate the greenhouse, especially after watering.

5. Remove plant debris: Do not leave weeds, old leaves, fallen fruits in the greenhouse. They are a breeding ground for infection. Burn them or bury them in compost (but only if the compost matures well) (Nonnecke, 1989).

9.3. Major Tomato Diseases in the Greenhouse

Late Blight (Phytophthora infestans)

Stem phytopathology: late blight (Phytophthora infestans) causing drying and constriction of the stem.

Severe late blight infection of a tomato stem. The upper part of the stem is greatly thinned, with deep dark‑brown necrotic lesions that typically constrict the stem, leading to complete loss of turgor and wilting of the upper part of the plant. The pathogen is the oomycete Phytophthora infestans. Photo taken under high‑humidity climatic conditions (Hilo, Hawaii).

This is the most famous and dangerous fungal disease. Affects all parts of the plant: leaves (brown spots), stems (dark stripes), and fruits (brown, hard, sunken spots). Spreads rapidly under high humidity and moderate temperatures (13–18 °C) (Ahatov, 2010; Nonnecke, 1989).

Prevention: Adherence to humidity regime, preventive treatments with copper-containing preparations (Bordeaux mixture, "Oxychom," "Hom") during flowering and fruit set (Gavrish, 2005).

Treatment: At the first signs, spraying with systemic fungicides ("Ridomil Gold," "Tanous," "Quadris"). Carry out treatments according to the instructions, alternating preparations to prevent resistance.

Gray Mold (Botrytis cinerea)

Tomato leaf infection by grey mould (Botrytis cinerea).

Symptoms of fungal disease on tomato leaves: extensive greyish‑brown necrotic spots located along the midrib and at the base of leaf blades.

Fungal disease affecting stems (at wound sites), leaves, and fruits (especially during ripening). A fluffy gray coating appears on affected tissues. Particularly dangerous under high humidity and sharp temperature fluctuations (Ahatov, 2010).

Prevention: Ventilation, removal of lower leaves, avoiding stem wounds. Use of biopreparations (based on Trichoderma) for treating wounds (Gavrish, 2005).

Treatment: Spraying with preparations based on iprodione ("Rovral," "Switch"). Cut out affected tissues, capturing 2–3 cm of healthy tissue.

9.4. Major Tomato Pests in the Greenhouse

9.5. Folk Remedies: Is There a Place for Them?

Folk methods (spraying with soap solution, garlic infusion, tobacco decoction) can be effective at early stages of infection, as auxiliary means, and for prevention. However, with strong spread of diseases and pests, they are generally ineffective. Do not rely only on them in critical situations.

9.6. General Rules for Working with Chemicals

1. Read the instructions: Preparations may have different waiting periods (time from treatment to harvest). Be sure to observe them!

2. Alternate preparations: To prevent pests and diseases from developing resistance, do not use the same preparation constantly. Alternate active ingredients (Jones, 2008).

3. Safety: When working with chemicals, use protective gloves, a respirator, and goggles. Treat only in the morning or evening, in calm weather.

4. Biological preparations: Prefer biological preparations ("Fitoverm," "Trichoderma," "Bactofit"). They are less toxic to humans and the environment, although they act more slowly (Gavrish, 2005).

In the next, final chapter, we will discuss how to properly end the season to prepare the greenhouse for the next year.

10.1. Why is Proper Winding Down So Important?

After you have harvested the last fruits, the work in the greenhouse does not end. In fact, this is one of the most important stages, often ignored. If you just pull out the plants and close the greenhouse until spring, you leave inside an ideal incubator for diseases and pests.

• Plant residues are a breeding ground for infection. Fungal spores (late blight, gray mold, Fusarium), eggs, and pupae of pests (whiteflies, spider mites) overwinter on old stems, leaves, and roots (Nonnecke, 1989; Ahatov, 2010).
• Soil is depleted. Intensive fruiting removes a large amount of nutrients from the soil. If not replenished in autumn, the next harvest will be weaker (Jones, 2008).
• Structures get dirty. Dirt, dust, and pathogen residues settle on glass, polycarbonate, and frames. In spring, you will have less time for a quality clean-up.

The golden rule: you must finish the season as carefully as you started it. This rule will allow you to start from scratch every year, with clean and healthy soil, and significantly reduce the need for chemical treatments in the next season.

10.2. Step-by-Step Instructions for Ending the Season

10.3. Repair and System Preparation

In winter, when you have free time, check and put in order your equipment:

• Check the trellis: Assess the condition of the wire and supports. Tighten where necessary, replace worn elements.
• Check the irrigation system: Clean or replace drippers and filters. Drain water from pipes to prevent freezing in winter.
• Check the ventilation system: Clean fans and vents, lubricate opening mechanisms.
• Repair damage: Seal gaps and cracks in the frame and greenhouse covering. This will help retain heat and prevent pests and cold air from entering in spring (Jones, 2008).

Reminder: It is better to carry out all these works in autumn, before severe frosts hit. In spring, you will have more time for planting and caring for plants, rather than repairing and cleaning.

Conclusion

Growing tomatoes in a greenhouse is a fascinating journey into the world of microclimate management. It is not just a hobby, but a true art in which you are the conductor. The greenhouse gives you incredible opportunities: you can harvest several times more than in open ground, extend the season by months, and grow the most heat-loving and demanding varieties.

I hope this article has helped you understand the basic principles of this exciting process. Remember that the key to success is not rigid rules, but careful observation of your plants and the ability to adjust conditions in a timely manner.

Good luck and happy, bountiful harvests!