Watering

2.1. Turgor: The Basis of Cell Life

Water is what maintains the shape of every plant cell. When cells are saturated with water, they create internal pressure—turgor. It is turgor that gives leaves and stems their firmness. With a lack of water, turgor drops, and the plant begins to wilt.

But wilting is only the last, visible stage of the problem. Long before the leaves droop, with reduced turgor, all physiological processes slow down: stomata (microscopic openings on the leaves) close, cell growth stops, and the plant enters a state of stress (Jones, 2008). Even a short-term drop in turgor can reduce yield.

2.2. Transport of Nutrients

Water is the medium in which all nutrients move. Roots absorb mineral salts dissolved in water from the soil, and through the xylem (the plant's vascular system), this solution rises to the leaves and fruits. Water evaporating through the leaves (transpiration) creates a "pump" that pulls this solution upward (Hochmuth and Sideman, 2023).

This process is especially important for calcium—an element that moves extremely slowly through the plant and is responsible for the strength of cell walls. It is the disruption of calcium transport due to lack of water or high air humidity that leads to blossom-end rot of fruits (Heuvelink, 2018).

2.3. Photosynthesis and Respiration

Water is a direct participant in photosynthesis. The water molecule is split, and its atoms are incorporated into carbohydrates, which form the basis of the harvest (Jones, 2008). Furthermore, the stomata, through which the plant absorbs carbon dioxide (CO₂), are regulated precisely by the water regime. With a lack of water, stomata close, CO₂ absorption stops, and photosynthesis ceases.

Research shows that even under moderate water stress, photosynthesis slows down due to restricted gas movement through stomata and slowed water movement through vessels (Jones, 2008). Thus, lack of water directly limits the plant's ability to create organic matter—the basis of the future harvest.

2.4. Fruit Filling

Fruit formation and filling require a huge amount of water. During the period of active fruit growth, the plant consumes maximum water. In greenhouse conditions, one adult plant in the fruiting phase can consume up to 2–3 liters of water per day (Heuvelink, 2018). Most of this water goes not towards building tissues, but towards evaporation through the leaves—this process cools the plant and creates a flow of water that delivers nutrients to the fruits.

If water is insufficient, fruit growth slows down, they become smaller, and their quality decreases. Moisture deficit is especially critical during the period from fruit set to the beginning of ripening (Welbaum, 2015). It is at this time that even a short-term drought can lead to an irreversible reduction in yield.

2.5. Effect of Root Temperature

An interesting fact: the ability of a tomato to absorb water is strongly influenced by soil temperature. When the root zone temperature is below 18 °C, water absorption significantly decreases (Tindall et al., 1990, cited in Jones, 2008). This means that in cool weather, the plant may suffer from lack of water even in moist soil. Watering with cold water can worsen the situation by causing shock. This is why it is recommended to water tomatoes with water warmed to soil temperature, especially in greenhouses (Kotov and Adritskaya, 2016).

Why Do Water Needs Change?

Water consumption by tomatoes is determined by two main factors:

1. The size and activity of the leaf apparatus—the more leaves, the more water evaporates (transpiration).

2. The development phase—at different periods, the plant directs water to different processes: root and stem growth, flowering, fruit filling.

Additionally, actual water consumption is strongly influenced by external conditions: air temperature, humidity, solar radiation, wind strength. On a hot, sunny day, a plant can evaporate several times more water than on a cloudy and cool day (Heuvelink, 2018). Therefore, there is no fixed watering rate "for all occasions"—you need to focus on the condition of the soil and the plant. However, there are general principles for each phase.

Phase 1. Seedlings: Moderation and Caution

At the seedling stage, the tomato still has a very small root system, and leaves are just starting to develop. The need for water is low. The main danger during this period is overwatering, which leads to the development of root rots ("damping off") and waterlogging (Jones, 2008).

What to do:

• Water seedlings moderately, when the top layer of soil (about 1 cm) has dried out.
• Water should be at room temperature (not cold!) to avoid shocking the roots.
• Ensure good drainage—stagnant water in the tray is unacceptable.
• Water less often on cloudy days, slightly more often on sunny days, but always check soil moisture with your finger.

Why it works: The small volume of roots cannot quickly absorb a large amount of water. Excess moisture displaces air from the soil, roots suffocate, and pathogenic fungi get ideal conditions for development.

Phase 2. After Transplanting to the Ground: Caution, Adaptation!

Transplanting is a strong stress for the plant. Roots are damaged, absorbing capacity is reduced, and leaves continue to evaporate moisture. During this period, it's very easy to "overwater" the plant, especially in cool weather.

What to do:

• Immediately after transplanting, water the planting hole thoroughly to ensure good contact between roots and soil.
• Then, for 5–7 days, reduce watering if there is no extreme heat. This stimulates roots to grow deeper in search of moisture, making the plant more resilient later on (Atherton and Rudich, 1986).
• Resume regular watering when the plant starts to grow—when a new leaf or shoot appears.
• In hot weather, you can shade the plants for the first 2–3 days to reduce evaporation.

Why it works: Moderate "water hunger" immediately after planting forces roots to actively develop and explore a larger volume of soil. This lays the foundation for a robust plant that will better tolerate dry periods later.

Phase 3. Active Vegetative Growth: Increased Consumption

When the plant has established and begun to actively grow leaves and stems, its need for water increases. During this period, the future yield potential is formed.

What to do:

• Water regularly, maintaining soil moisture at 70–80% of field capacity (this is when the soil is moist, but water does not stand on the surface and does not squeeze out when squeezed in a fist) (Hochmuth and Sideman, 2023).
• Focus on the weather: in hot, dry weather, watering may be needed 2–3 times a week; in cool weather, once every 5–7 days.
• Wetting depth—at least 20–30 cm, so roots do not remain in the surface layer.
• In the greenhouse during this period, maintain moderate air humidity (around 60–65%)—this promotes better nutrient uptake (Kotov and Adritskaya, 2016).

Why it works: The tomato forms a powerful leaf apparatus through which a large amount of water evaporates. If there is not enough water, leaf growth slows down, and the plant will not be able to "feed" future fruits.

Phase 4. Flowering and Fruit Setting: Stability is Key

The most critical and sensitive period. It is during flowering and fruit setting that the tomato reacts extremely acutely to fluctuations in moisture. Stress from lack of water can lead to flower and fruit drop, and sudden overwatering after drought can lead to fruit cracking in the future.

What to do:

• Keep the soil consistently moist, avoiding drying out.
• Water regularly, preferably more often but in smaller amounts, rather than rarely and heavily.
• If the weather is dry and hot, watering may be needed every other day or even daily (Atherton and Rudich, 1986).
• Avoid watering with cold water—it can cause shock and flower drop.

Why it works: The future harvest is formed during this period. With a lack of moisture, the plant activates a self-preservation mechanism: it sheds some flowers and fruit sets to avoid wasting water on fruits it cannot "hydrate." Flower drop often occurs not immediately, but a few days after the stress, so gardeners don't always connect cause and effect.

Phase 5. Fruit Filling: Maximum Consumption

The most "water-intensive" period. Once fruit sets begin to grow and fill, the need for water peaks. It is at this time that the plant uses the most water (Welbaum, 2015). If water is lacking, fruits grow slowly, become small, hard, and their taste deteriorates.

What to do:

• Ensure regular, abundant watering so the soil is always moist at root depth (30–40 cm).
• In hot weather, water 2–3 times a week, or even daily if the soil dries out quickly.
• In greenhouses during this period, maintain soil moisture at 80–85% of field capacity (Kotov and Adritskaya, 2016).
• If using drip irrigation, increase the duration or frequency of cycles.

Why it works: Tomato fruits consist of 90–95% water (Jones, 2008). Every gram of fruit growth requires water intake. Additionally, water transports sugars and nutrients to the fruits, shaping their taste and aroma. If the plant experiences thirst during this period, yield drops irreversibly—fruits already formed will not "catch up" in size.

Phase 6. Ripening: Moderation for Quality

When fruits begin to turn red (or yellow, depending on the variety), their growth slows down. Now, excess water can be harmful: fruits become watery, lose sugar content, and, most importantly, start cracking.

What to do:

• Reduce watering: water only when the soil has dried to a depth of 5–7 cm.
• If rainy weather sets in or is forecast, stop watering altogether.
• Avoid sharp fluctuations in moisture—this is the main cause of fruit cracking (Kotov and Adritskaya, 2016).
• In the greenhouse, reduce air humidity by increasing ventilation.

Why it works: During ripening, the fruit skin becomes less elastic. When abundant watering is given after a dry period, water quickly rushes into the fruits, they swell, and the skin cannot withstand it—cracks appear. Furthermore, moderate water deficit increases the content of sugars and solids, improving taste (Atherton and Rudich, 1986). That's why many experienced gardeners reduce watering 2–3 weeks before the main harvest so that the fruits are sweeter and more aromatic.

How to Know You Are Watering Correctly?

There are no universal "liters per bush" because every garden has its own microclimate, soil, and variety. But there are simple guidelines:

1. Check the soil. At a depth of 10–15 cm, it should be moist but not wet. Take a handful of soil: if it easily forms a ball but doesn't stick to your hands—moisture is optimal.

2. Observe the leaves. Healthy tomato leaves are firm, bright green, not curled. Drooping, dull leaves are a sign of water shortage. Leaf curling into a "boat" shape during the day can be a protective reaction to heat, but if it persists in the morning—it's a signal.

3. Consider the weather. In hot and windy weather, water more often; in cloudy and cool weather, less often.

4. Remember mulch. A layer of organic mulch (straw, mown grass, compost) significantly reduces evaporation and evens out soil moisture, reducing the need for watering (Welbaum, 2015).

The Main Principle

Do not water "on a schedule"—water according to the plant's needs. On a hot day, a bush can "drink" 2–3 liters of water, while on a cool day—half as much. Regularly check the soil, observe the weather and the condition of the plants, and you will always find the right regime.

What Determines Watering Frequency?

Watering frequency is the interval between waterings. It depends on how quickly the soil loses moisture. The rate of moisture loss, in turn, is determined by four main groups of factors:

1. Soil properties—how quickly water leaves the root zone (absorbs, drains, evaporates).

2. Weather conditions—temperature, air humidity, solar radiation, wind.

3. Plant development phase—water needs change (as we saw in Chapter 3).

4. Watering method and presence of mulch—affects evaporation and wetting depth.

Let's examine each factor in detail.

1. Soil Type: The Main Factor in Frequency

Different soils retain moisture differently. This is determined by their texture—the ratio of sand, silt, and clay particles (Hochmuth and Sideman, 2023). It is the texture that determines how often you need to water.

Sandy and loamy sand soils.

• Characteristic: Water quickly goes deep, the soil has low water-holding capacity (available water only 0.06–0.12 mm per 1 cm of soil) (Kemble et al., 2022).
• Watering frequency: Frequently, but in small doses. In hot weather—every 1–2 days, sometimes daily. The soil dries out quickly, and roots do not have time to "reach" moisture in the deeper layers.
• Risks: Rapid drying, especially during flowering and fruit filling. It's easy to overwater if you don't check moisture—water simply goes deep, leaving roots in the dry top layer.
• Advice: Use drip irrigation and mulching to reduce watering frequency and water loss.

Loamy and clayey soils.

• Characteristic: Water is retained better, water-holding capacity is higher (0.14–0.23 mm per 1 cm of soil). The soil dries out more slowly (Kemble et al., 2022).
• Watering frequency: Less often, but more abundantly. Watering once every 5–7 days, and in cool weather—once every 10–12 days. The soil remains moist at root depth for a long time.
• Risks: Water stagnation, overwatering, lack of oxygen for roots. Especially dangerous in rainy weather or with frequent watering.
• Advice: Check moisture at a depth of 20–30 cm—if it's still wet there, don't water. Ensure good drainage.

Peaty (organic) soils.

• Characteristic: Very high water-holding capacity (sometimes excessive). The soil can stay wet for a long time.
• Watering frequency: Very rarely. One watering every 10–14 days in the absence of rain might suffice.
• Risks: Easy to overwater, especially if the soil is poorly drained.
• Advice: Focus on the visual condition of plants and the moisture of the top layer (5–7 cm).

Determining soil type "by eye."

A simple test: take a handful of moist soil, squeeze it in your fist. If it falls apart—it's sand. If it forms a lump but crumbles easily—sandy loam or light loam. If the lump holds its shape, doesn't crumble, but doesn't stick—loam. If it sticks to your hands and shines—clay. Based on this, you can roughly estimate the watering frequency.

2. Weather Conditions: Temperature, Sun, Wind

Evaporation of water by the plant (transpiration) and from the soil surface depends heavily on the weather (Heuvelink, 2018).

• Air temperature: When temperature rises by 10 °C, evaporation nearly doubles. In heat above 30 °C, watering may be required daily or even twice a day (in extreme heat and light soils). In cool weather (15–20 °C), the interval increases to 5–7 days.
• Solar radiation: On a bright sunny day, the plant evaporates 2–3 times more water than on a cloudy day. During cloudy periods, watering is reduced—the soil dries slower.
• Air humidity: In dry air (below 50%), evaporation increases. In humid weather or in a greenhouse with high humidity (75–85%), evaporation decreases (Kotov and Adritskaya, 2016). In southern arid regions, watering frequency increases.
• Wind: Strong wind increases evaporation from the soil surface and transpiration. In windy weather, water more often.

Practical conclusion: On a hot, sunny, windy day, water more often than on a cloudy, cool one. Focus not on the calendar, but on the weather "here and now."

3. Plant Development Phase (recall Chapter 3)

Watering frequency is directly related to the phase:

• Seedlings and first time after transplanting: rarely, to stimulate root growth and avoid rot.
• Active vegetative growth: moderately often, maintaining moisture.
• Flowering: often, but without overwatering—stability is paramount.
• Fruit filling: most often—during this period water consumption is maximum, and the soil dries out faster.
• Ripening: less often, to improve taste and avoid cracking.

Thus, in June-July, when fruits are filling, watering frequency will be highest. By August-September, as they ripen, it can be reduced.

4. Air Humidity (especially in greenhouses)

In a greenhouse, air humidity strongly influences watering frequency and water consumption. At high air humidity (above 80%), transpiration decreases, the plant evaporates less, and the soil stays moist longer. But high humidity increases the risk of fungal diseases. In greenhouses, it's recommended to maintain humidity at 60–75% during fruiting (Kotov and Adritskaya, 2016). This means watering frequency in a greenhouse may be lower than in open ground at the same temperature.

How to Determine When to Water?

The most reliable way is not to guess, but to check soil moisture.

• Depth test: Stick a stick into the soil to a depth of 10–12 cm. If the soil is dry at that depth—water. If moist—wait.
• "Ball" test: Take a lump of soil from a depth of 15–20 cm, squeeze it. If it crumbles—the soil is too dry, needs watering. If it forms a ball but doesn't stick to hands—moisture is optimal. If it sticks and shines—overwatering, postpone watering.
• Visual signs: If tomato leaves start losing firmness during the day—that's a signal. But it's better not to let it get to that point, especially during flowering and fruit setting.

General Recommendations on Frequency (approximate guidelines)

These figures are not rigid norms, but a starting point for your observations:

With mulch, frequency can be reduced by 20–30%. With drip irrigation, frequency is increased (it supplies water slowly), but the duration of each watering is adjusted to wet the desired layer.

The Main Rule

Water when the soil demands it, not when it's convenient for you. Watering frequency is a tool you adjust to your soil, weather, and plant. Regularly check soil moisture, observe leaf condition, consider the weather forecast. Then the tomato will reward you with a stable harvest without stress and disease.

How to Choose a Watering Method?

The ideal way to water tomatoes should meet three requirements:

1. Water goes directly to the root zone—not on leaves, not on stems, but exactly where the absorbing roots are.

2. Watering is uniform and metered—without sharp fluctuations in moisture.

3. Leaves stay dry—wet leaves are a direct path to fungal diseases (late blight, early blight, gray mold).

Based on these principles, we will evaluate the different methods. And let's start with the most efficient one.

1. Drip Irrigation: The Gold Standard

Drip irrigation is a method where water is supplied slowly, literally drop by drop, directly to the root zone of each plant. This method is recognized as the most effective for tomatoes both in open ground and in greenhouses (Heuvelink, 2018; Kemble et al., 2022).

How it works: Through pipes or tapes laid along the row, water flows to emitters located near each plant. The emitter releases 1–2 liters of water per hour. The soil is moistened evenly to a depth of 30–40 cm, wetting exactly the volume where the roots are. The soil surface remains dry.

Advantages:

• Water savings: up to 50–70% compared to sprinkling and up to 30–40% compared to furrow irrigation. Water is not wasted on evaporation from the surface and does not wet the rows (Kemble et al., 2022).
• Leaves stay dry: the risk of late blight, early blight, and powdery mildew is greatly reduced.
• Stable moisture: no sharp fluctuations between waterings—water is supplied constantly in small portions.
• Fertigation: soluble fertilizers can be supplied simultaneously through the system, significantly increasing the efficiency of feeding (Hochmuth and Sideman, 2023).
• Reduced weeds: rows remain dry, preventing weed seeds from germinating.

Disadvantages:

• Higher cost of equipment (tapes, fittings, filters, control system).
• Requires regular monitoring—emitters can clog (sand, sediment, algae). It is recommended to use filters and periodically flush the system.
• Need for proper pressure—too low or high pressure disrupts uniformity.

Recommendations:

• For small plots, you can use ready-made drip irrigation kits or assemble a system yourself from drip tape and connecting fittings.
• Place the drip tape 10–15 cm from the plant stem.
• Turn on the system in the morning so the soil has time to warm up. In heat, evening watering is acceptable, but avoid watering at night to prevent creating high humidity.
• Adding mulch (more on this below) over the drip tape increases efficiency by another 20–30%.

Why it works: With drip irrigation, water is supplied slowly, and the soil has time to absorb it without forming a crust or puddles. Constant moistening of the root zone without overwatering is exactly what the tomato needs: roots are always in optimal conditions, without stress from drying out or water stagnation.

2. Watering at the Root (using a watering can or hose)

This is the classic method used by most gardeners. Water is supplied directly to the base of the plant, without getting on the leaves.

How to do it correctly:

• Use a watering can without a "rose" or a hose with a breaker, directing the stream into the root circle, not onto the stem.
• Water slowly, allowing the water to soak in. Do not pour the entire amount at once—let the soil "receive" the water in layers.
• Create a small depression (basin) or soil ridge around the plant—this will prevent water from spreading.

Advantages:

• Simplicity: no complex equipment required.
• Full control: you see how much water each plant receives.
• Leaves stay dry with careful watering.

Disadvantages:

• Labor-intensive: each bush needs to be watered individually. With a large number of plants, this becomes a problem.
• Risk of erosion: a strong stream can wash away soil and expose roots.
• Unevenness: easy to make mistakes with volume—one bush gets more, another less.
• Needs access to each plant: difficult in dense plantings.

Recommendations:

• Water only in the morning or evening to prevent instant evaporation.
• Use a hose with a spray pistol and water at the root, not from above.
• If plants are planted in rows, you can make furrows along the row and water through them—this is faster than watering each bush separately.
• After watering, be sure to loosen the soil (if there is no mulch) to break the crust.

Why it works: When watering at the root, water reaches exactly where the active absorbing roots are. This is a direct and natural way of supplying moisture to the plant. If done carefully and regularly, without overwatering, the results will be excellent.

3. Furrow Irrigation (Flood)

This method is often used in large open fields where it's not possible to install a drip system. Shallow furrows are cut between rows of tomatoes, and water is run along them.

How it works: Water is supplied along furrows running along or between rows. It flows, gradually soaking into the soil and moistening the root zone of plants on both sides of the furrow. After the water has soaked in, the furrows are covered with dry soil to reduce evaporation.

Advantages:

• Relative simplicity for large areas.
• Can be automated: open a valve—water flows along the furrows.
• No cost for drip equipment.

Disadvantages:

• High water consumption—a significant part goes to evaporation and deep percolation.
• Uneven wetting: plants located closer to the water supply point get more.
• Leaves can get wet if furrows are too close, especially with high pressure.
• Can lead to soil compaction between rows.
• Not suitable for greenhouses and small plots.

Recommendations:

• Make furrows 10–15 cm deep, at a distance of 30–40 cm from the stems (to prevent water from flooding the stem base).
• Water using furrows only in cool weather or in the morning, so water has time to soak in before the heat.
• Use mulching (see below) to reduce evaporation between waterings.

Why it works: Water in the furrows wets a large volume of soil, and tomato roots, which spread wide, can actively explore it. However, due to the abundance of water, some is used inefficiently, so this method is better suited for arid regions with cheap water or when growing on large areas.

4. Mulching—A Moisture Stabilizer

Mulching is not a watering method, but a critical tool for managing moisture. A layer of organic mulch (straw, grass, sawdust, compost, mown grass, bark) or plastic film (black or clear) significantly reduces water evaporation from the soil surface (Welbaum, 2015).

How it works: Mulch creates a barrier between the soil and the air. Sunlight does not heat the soil directly, wind does not blow moisture from the surface. As a result:

• Evaporation is reduced by 30–50%.
• The soil warms up slower (in summer) and cools down slower (at night)—daily temperature fluctuations are reduced.
• A crust does not form, and water penetrates deeper.
• Plant roots are in more stable conditions.

Types of mulch:

1. Organic: mown grass, straw, hay, compost, bark, leaf litter. It decomposes, enriching the soil with organic matter, but it needs to be replenished as it settles.

2. Plastic film: black polyethylene film is the most effective method for field tomatoes. It not only retains moisture but also warms the soil in spring and suppresses weeds. In hot climates, white or reflective film is used to prevent overheating (Kemble et al., 2022).

Mulching recommendations:

• Apply mulch 5–8 cm thick after the soil has warmed up and the plants have grown (to prevent rot at the stem base).
• If using film, be sure to make holes for the plants and ensure drainage so water doesn't stagnate.
• Replenish organic mulch as it decomposes.
• With drip irrigation, mulch is especially effective—it retains moisture and reduces watering frequency by another 20–30%.

Why it works: Mulch breaks the direct contact of soil with air and sun, so water stays in the soil instead of evaporating into the atmosphere. It also protects the soil from overheating, which is especially important for tomato roots during hot periods. Research shows that using mulch can reduce watering needs by 25–40% (Kemble et al., 2022; Welbaum, 2015).

Comparison Table of Watering Methods

Which Method to Choose?

• For greenhouses and small plots: undisputed leader—drip irrigation. It provides the best control, saves water, and reduces diseases.
• For large open fields with cheap water and high planting density—furrow irrigation or root watering with hoses, but with mandatory mulching.
• For hobbyists and gardeners: watering at the root from a watering can or hose + organic mulch—this is the ideal combination of simplicity and efficiency.
• Sprinkling (watering from above) for tomatoes is not recommended due to the high risk of fungal diseases.

Main idea: The best watering method is one that delivers water to the roots without wetting the leaves and does it regularly, without sharp jumps in moisture. Drip irrigation is the gold standard, but in its absence, you can get excellent results with root watering combined with mulching.

Open Ground

Greenhouse

Comparison Table: Open Ground vs. Greenhouse

Main Takeaway

In open ground, you adapt to the weather (rain, wind, sun). In the greenhouse, you create the weather for the plant. But in both cases, the main thing is stable moisture in the root zone without overwatering. The difference lies only in how you achieve this: in the field—with weather adjustments, in the greenhouse—with strict control of air humidity, water temperature, and ventilation.

Proper watering is a balance. Both in open ground and in the greenhouse, it requires attention and regular soil checks, not following a fixed schedule.

Why is it Important to Distinguish the Signs?

Lack and excess of water give similar external symptoms—wilting, yellowing, dropping. But the causes are completely different, and the treatment is also different. If you start watering an overwatered plant, you will finish it off. If you stop watering one suffering from drought, the same. So it's critical to determine exactly what you are dealing with. Let's start with the simplest—describing the symptoms by group.

Symptoms of Water Deficiency

Lack of moisture is water stress. The plant cannot compensate for evaporation from the leaves, and internal processes are disrupted.

Symptoms of Excess Water

Excess water is as dangerous as deficiency but acts differently. Overwatering leads to oxygen deficiency at the roots, impaired nutrition, development of rot, and diseases.

How to Distinguish Water Stress from Disease or Nutrient Deficiency?

This is the main problem. Symptoms are often similar. The key difference is speed and massiveness:

• Water stress manifests quickly (within hours or days) and affects all or many leaves and fruits.
• Nutrient deficiency develops slowly (weeks) and often affects specific parts (lower leaves for nitrogen deficiency, young ones for iron deficiency).
• Diseases often show spots, plaque, discoloration and develop locally, not on the whole plant at once. With water stress, there is no plaque—the plant simply "wilts" or "yellows" without rotting spots (unless it's rot from overwatering).

The main check—soil moisture. If in doubt, check the soil at a depth of 10–15 cm. Wet? Then the problem is not a lack of water. Dry? Then, most likely, the plant is suffering from drought.

Practical Diagnosis Scheme

1. Look at wilting. If leaves wilt, but the soil is wet—it's overwatering. If they wilt and the soil is dry—underwatering.

2. Look at color. Yellow and drooping leaves with wet soil—overwatering. Yellow and curled with dry soil—lack of moisture.

3. Check the fruits. Blossom-end rot, cracking, flower drop—almost always the result of unstable watering, not specifically lack or excess.

4. Remember the weather. If after a long heat there was heavy rain—expect cracking. If there was a drought and you watered heavily—the same.

Signs of Water Stress

Mistake 1. Watering on a schedule, not according to plant needs

This is the most common mistake. Gardeners water "once every three days" or "every morning," without paying attention to the weather, growth phase, and soil condition.

What it threatens:

• In cool weather—overwatering, root rot.
• In hot weather—underwatering, stress, small fruits.
• Sharp transitions from drying out to overwatering—fruit cracking and blossom-end rot (Jones, 2008; Heuvelink, 2018).

How to do it correctly:

Focus on soil moisture, not the calendar. Check the soil at a depth of 10–15 cm (with a finger or stick). If it's dry there—water. If wet—wait. Consider the growth phase (Chapter 3) and the weather forecast. A schedule is just a guideline, not a law.

Simple rule: "Better to check than to guess."

Mistake 2. Watering with Cold Water

This is especially relevant for greenhouses, but also happens in open ground. Water from a well, borehole, or even a hose heated only on the outside by the sun can be significantly colder than the soil.

What it threatens:

• Root shock: at water temperatures below 18 °C, the absorbing capacity of roots sharply decreases (Tindall et al., 1990, cited in Jones, 2008).
• Slowed growth, leaf yellowing, flower and fruit drop (Kotov and Adritskaya, 2016).
• In cold, wet soil, root rots actively develop.

How to do it correctly:

Use water at room temperature (20–25 °C). In a greenhouse, this is easy—place a tank or barrel inside so the water warms up naturally. In open ground—fill containers in advance, in the sun. If you cannot warm the water, water in the morning when the soil is still cool—the contrast will be less than watering in the heat. Never water tomatoes with cold water straight from the hose tap.

Mistake 3. Watering on Leaves (Sprinkling)

Many gardeners like to "refresh" plants with sprinkling, especially in the heat. For tomatoes, this is one of the most dangerous mistakes.

What it threatens:

• Wet leaves are an ideal environment for fungal diseases: late blight, early blight, powdery mildew, gray mold (Kotov and Adritskaya, 2016; Kemble et al., 2022).
• Water drops on leaves act like lenses, increasing sunburn.
• Water getting on flowers hinders pollination and can cause drop.

How to do it correctly:

Water only at the root. Use a watering can without a "rose," a hose with a breaker, directing the stream into the root circle. Ideally—drip irrigation, which does not wet the leaves at all. If you really want to spray the leaves in the heat for cooling, do it early in the morning so they dry by evening, and only in exceptional cases. But it's better to use shading and mulch to reduce soil and air temperature.

Mistake 4. Shallow Surface Watering

When water wets only the top 5–10 cm of soil, roots do not develop deep, remaining in the surface layer.

What it threatens:

• Roots become shallow and dry out easily in the heat.
• The plant becomes less resistant to drought.
• Nutrition is disrupted, as the bulk of the roots are in the top layer, where fertilizers are quickly leached (Hochmuth and Sideman, 2023).

How to do it correctly:

Water so that water wets the soil to a depth of 30–40 cm (the depth of the main root system of an adult tomato). Check this with a stick after watering. Deep, infrequent watering is better than frequent surface watering. With drip irrigation, simply leave the system on longer for deeper penetration. The norm for an adult plant is at least 5–10 liters of water per watering (depending on soil and plant age).

Mistake 5. Abrupt Transition from Drought to Abundant Watering

A mistake that most often occurs after a long heat wave or when the gardener hasn't watered for a while and then decides to "make up for lost time" by giving a lot of water at once.

What it threatens:

• Fruit cracking—the most characteristic reaction (Welbaum, 2015; Jones, 2008).
• Blossom-end rot—with a sudden influx of water, calcium transport to fruits is disrupted.
• Stress for roots: a sharp change in moisture can lead to the death of thin absorbing root hairs.

How to do it correctly:

If the soil is very dry, do not flood it immediately. It is better to do 2–3 moderate waterings with an interval of several hours (or the next day). First, moisten the top layer, then wet it deeper. This gives the roots time to adapt and reduces the risk of cracking. In general, try not to allow severe drying during fruit filling and ripening—this is the most dangerous period for sharp fluctuations.

Mistake 6. Stopping Watering When Fruits Ripen (Too Early)

Many have heard that "for sweetness, tomatoes should be watered less" and abruptly stop watering as soon as the fruits start to turn red.

What it threatens:

• Premature cessation of watering stops the growth of fruits that have not yet reached their maximum size (Welbaum, 2015).
• Fruits may become more watery? No, on the contrary, with a lack of water, they become hard, but not sweet (sugars are formed during normal photosynthesis, which requires water).
• Ripening may slow down due to stress.

How to do it correctly:

Reduce watering gradually, starting 2–3 weeks before the expected harvest, but do not stop completely. The soil should remain moderately moist, especially if it's hot. It's better to water less often (once every 5–7 days), but maintain moisture at root depth. Complete cessation is permissible only with obvious overwatering or prolonged rains. In dry weather, even ripening fruits need some water to maintain leaf turgor and photosynthesis.

Mistake 7. Ignoring Mulching

Many gardeners underestimate the role of mulch or consider it extra work.

What it threatens:

• The soil dries out faster, requiring more frequent watering.
• Moisture fluctuations are sharper, leading to cracking and blossom-end rot.
• The soil overheats, roots suffer from heat.

How to do it correctly:

Be sure to use mulch: organic (straw, mown grass, compost) or film. A layer of mulch 5–8 cm thick reduces evaporation by 30–50%, stabilizes soil temperature, and reduces watering frequency (Welbaum, 2015; Kemble et al., 2022). Even if you have drip irrigation, mulch is not an addition but an important part of the system. It pays off by reducing water costs and improving fruit quality.

Mistake 8. Wrong Time for Watering

Watering during the peak heat, when the sun is at its zenith, is another common mistake.

What it threatens:

• Most of the water will evaporate without being absorbed.
• Drops on leaves can cause sunburn.
• When water hits hot ground, a greenhouse effect occurs, and roots can "cook."

How to do it correctly:

The best time for watering is early morning (before 10–11 AM) or evening (after 6–7 PM), when the sun is not as active and the wind subsides. Morning watering is preferable: leaves dry out during the day, reducing the risk of fungal diseases. Evening watering is acceptable, but it increases air humidity at night, which is especially undesirable in a greenhouse. In the heat, watering at other times is permissible, but only at the root, so water does not get on the leaves.

Mistake 9. Incorrect Assessment of Different Varieties' Needs

Different tomato varieties may have different water needs. For example, indeterminate (tall) varieties with a larger leaf apparatus consume more water than determinate (short) ones. This is especially noticeable in greenhouses, where indeterminate varieties grow for 6–9 months.

What it threatens:

• Overwatering or underwatering for a specific variety, reducing yield.

How to do it correctly:

Consider the variety's characteristics. Large-fruited and tall varieties require more abundant and regular watering, especially during fruit filling. Short, early-maturing varieties—less. Study the variety's characteristics, usually indicated on the package. But the main thing—still check soil moisture and plant condition, rather than relying on average norms.

Mistake 10. Underestimating the Role of Soil Aeration

After each watering, a crust forms on the soil surface, preventing air from reaching the roots.

What it threatens:

• Root respiration worsens, they absorb water and nutrients less effectively.
• Conditions are created for the development of root rots.

How to do it correctly:

After watering, when the soil has dried slightly but still retains moisture, be sure to loosen the top layer to a depth of 3–5 cm (if there is no mulch). This breaks the crust and improves aeration. In greenhouses, this is especially important. If you have mulch, loosening is not required—it itself prevents crust formation.

Conclusion: The Main Advice on Watering

Proper watering of tomatoes is an art of balance. There is no universal formula suitable for all cases. But there is a simple and reliable approach:

1. Check the soil (don't guess, don't blindly follow a schedule).

2. Water at the root (not on the leaves).

3. Wet deeply (30–40 cm), don't limit yourself to surface moistening.

4. Consider the weather and growth phase (don't water the same way always).

5. Avoid sharp moisture fluctuations—this is the main enemy of fruit quality.

6. Be sure to use mulch—it's your main assistant in stabilizing the regime.

7. Water in the morning with warm water, especially in the greenhouse.

The tomato is a grateful plant. It responds to proper care with a generous harvest of large, tasty, healthy fruits. And watering is one of the foundations of this success.

May your tomatoes be juicy, sweet, and crack-free!