Should You Water Tomatoes Often?

Should tomatoes be watered often? A complete guide based on climate and soil

• Context :The question of watering tomatoes arises for every gardener. An excess of water can promote diseases, while a lack of water can hinder growth and production. There is even abuzz around “waterless tomatoes”, which claims to grow without any watering – hence the importance of untangling myth from agronomic reality.
• Current issue :With increasingly frequent drought episodes, the rational use of water in the garden is a major concern. It is therefore necessary to find a balance betweensaving waterandensuring an optimal productionof tomatoes.
• Objective of the article :To provide acomplete guidefor watering tomatoes in aneffective and rational, based on scientific data (concept ofETP, agronomic trials) and taking into account theclimaticandedaphicfactors (nature of thesoil). We will seehow much water to provide, at what frequency, and how to adapt irrigation according to conditions, without giving in to extremes or preconceived ideas.

Climate and evapotranspiration: the influence of weather conditions on water needs

• Variable water needs:Tomatoes are composed of ~90-95% water, which explains that their growth strongly depends on water supply. These needsvaryaccording to theclimate: temperature, sunlight,windand ambient humidity.

To create 1 molecule of sugar, a plant needs 6 molecules of water.

How a plant drinks and feeds: understanding plant functioning

A plant, unlike an animal,does not have a heart or a pumpto circulate its fluids. Yet, it continuously "drinks" to live and grow. So, how does it do it?

1. Water absorption by the roots

Soil water is absorbed by theroot hairslocated at the tip of the roots. It also contains dissolvedminerals (nitrogen, potassium, calcium…) essential for the plant's nutrition. (azote, potassium, calcium…) essentiels à la nutrition de la plante.

But this water does not stay in the roots: it must travel up to the leaves, sometimes over a meter high in certain species. This is where a central phenomenon comes into play:evapotranspiration.

2. Evapotranspiration: the engine of sap circulation

Since the plant has no heartor active circulatory system, it is theloss of water through the leaves– called – appelée transpiration– which creates acontinuous suctionfrom the roots.

This phenomenon is calledevapotranspiration :

• Evaporationof water from the soil
• Transpirationof water through the stomata of the leaves

👉 As water escapes through the leaves, it creates adepressionin the conducting vessels (thexylem), which“pulls” the water upwardthroughout the plant.

This passive but very powerful mechanism allows a plant to circulateliters of water each daywithout a pump or motor organ.

3. Mineral nutrition and energy production

In addition to water, the roots absorbmineral elementsthat circulate with the raw sap. Once in the leaves, these elements participate in the production ofsugarsthrough another vital process: thephotosynthesis, which we will see just after.

To drink (and capture minerals from the soil), a plant must evapotranspire

"Disclaimer – Framework and objectives of the figures presented"

In this article, theamounts of water mentioned(which may shock some...) and theorders of magnitude of yieldcorrespond to situations where one seeks toto express the maximum agronomic potential of the tomato, under controlled conditions and without major limiting factors (water, nutrition, soil structure).

For reference, the yields used are as follows:

• 6 to 10 kg/m² in the field, under controlled cultural conditions consistent with a productive garden or well-managed outdoor vegetable farming;
• 40 to 50 kg/m² in greenhouses, with precise management of irrigation, fertility, and climate;
• up to70 kg/m² and more in highly controlled environments(high-tech greenhouses, soilless, fine climate and nutritional management).

It should also be noted that the water volumes are given for 1m² of cultivation, and that in seeking to optimize yields, it is advisable to cultivate between 2 and 3 plants per m² (the volumes are not stated for one plant).

An example of a tomato (zebra pineapple) that expresses its full potential (about 50kg/m² over a season).

These figuresare not provided for comparison purposes, nor to promote intensive or productivist agriculture. They serve only asagronomic benchmarks, allowing for:

• understandingwhat level of water requirement corresponds to a given yield objective ;
• illustrating the direct link betweenwater availability, physiological functioning of the plant, and biomass production ;
• helping everyone toreason and adapt their practices.depending on personal goals, context (climate, soil, access to water), and values.

It is entirely possible – and legitimate – to aim for:

• more modest yields,
• a voluntary reduction in water inputs,
• or a more extensive and resilient approach,

provided that onetakes responsibility for the agronomic consequences(fruit size, number of tomatoes, consistency of production).

 The goal of this article is therefore not to say"how much one must absolutely irrigate", but to provide aframework for understandingto move away from dogmatic discourses (irrigate everything / never irrigate) and allow forinformed, coherent, and responsible choices..

Definitions: ETP, RU, and Kc

1. ETP — Potential Evapotranspiration

Potential evapotranspiration (ETP) is the amount of water (expressed in millimeters per day or per week) that would be evaporated by the soil and transpired by a well-watered reference vegetation, upon given climatic conditions (temperature, radiation, wind, humidity).

• 1 mm of ETP = 1 liter of water lost per m²
• ETP calculated using the Penman-Monteith FAO-56 formula (international standard)
• Local data available via Météo-France, Agrymet, or FAO ClimWat

 ETP reflects the climatic demand for water. The hotter, drier, sunnier, and windier it is, the higher the ETP.

2. RU — Useful Soil Reserve

The Useful Reserve (UR) corresponds to the amount of water that the soil can store and that is actually usable by plants between the moment the soil is saturated and the moment the plants wilt (permanent wilting point).

It depends on:

• The soil texture (sand, silt, clay)
• The depth explored by the roots
• The structure and organic matter content

Average UR values (in mm/meter of soil):

• Sandy soil: 40 to 70 mm/m
• Silty or silty-clay soil: 100 to 150 mm/m
• Deep clay soil: up to 180 mm/m

A UR of 100 mm/m indicates that the soil contains 100 liters of usable water per m² for each meter of root depth.

3. Kc — Crop coefficient

The crop coefficient (Kc) adjusts the ETP to the reality of a given crop. It depends on:

• The type of plant
• The stage of development
• The ground cover

Formula:

ETR = Kc × ETP

where ETR is the actual evapotranspiration of the plant.

Typical values:

• Tomato in vegetative growth: Kc ≈ 0.5–0.7
• Tomato in full fruiting: Kc ≈ 1–1.2
• Low transpiration crops (garlic, chickpeas): Kc ≈ 0.2–0.4

Kc allows converting a climate (ETP) into the water needs specific to the crop.

Numerical examples: tomatoes vs chickpeas, in Toulouse and Geneva

Common assumptions

• Study area: 1 m²
• Period: July (hot summer)
• Deep loamy soil: RU = 120 mm/m, root depth = 0.4 m for tomato, 0.3 m for chickpea

• Useful RU:

  • Tomato: 120 × 0.4 = 48 mm
  • Chickpea: 120 × 0.3 = 36 mm

A. Estimation of weekly water needs

1. Average climatic data in July

2. Weekly needs according to the crop

a. Tomato in full fruiting (Kc = 1.1)

• Toulouse:

  • ETR = 1.1 × 38.5 = 42.35 mm/week
  • That is 42.35 liters/m²/week

• Geneva:

  • ETR = 1.1 × 33.6 = 36.96 mm/week
  • That is ~37 liters/m²/week

b. Chickpea in vegetative phase (Kc = 0.3)

• Toulouse:

  • ETR = 0.3 × 38.5 = 11.55 mm/week
  • That is ~11.6 L/m²/week

• Geneva:

  • ETR = 0.3 × 33.6 = 10.08 mm/week
  • That is ~10 L/m²/week

👉 Conclusion: on the same area, tomatoes consume about 3 to 4 times more water than chickpeas. Hence the importance of adapting irrigation to the crop and the climate.

B. Simulation of rational irrigation

Let's take the case of a gardener in Toulouse with a crop of tomatoes (2 to 3 plants) on 1 m², soil with a water retention capacity (RU) of 48 mm (as mentioned above). If the week is dry and the evapotranspiration rate (ETR) is 42 mm:

• The watering must compensate for 42 mm – any potential rainfall.
• If there is no storm or rain (and the RU is exhausted), plan for 1 or 2 waterings totaling 42 liters/m²/week.
• For example: 2 waterings of 21 liters/m² each, spaced 3–4 days apart, to moisten the depth of the soil.

The calculations presented above correspond to adeliberately extreme case: very dry conditions, during peak fruiting, outdoors with wind, and the goal ofexploiting the full productive potential of the plants(maximum yield). These values may be surprising – even shocking to some – but they represent atheoretical maximum, useful forestablishing a scale of magnitudeand understanding the forces at play (climate, water, plant physiology).This is neither a standard nor a universal goal.

It is neither a standard nor a universal objective.

 It is up to each person to adapt these benchmarks to their soil, climate, goals, and beliefs.

Soil type: water retention and rooting of tomatoes

• Soil water retention capacity (RU):The soil acts like a reservoir. Aclay or loamy soilretains a lot of water (highuseful reserve), allowing for longer intervals between waterings. In contrast, asandy soildrains water quickly (low reserve), which requires more frequent and smaller amounts of watering each time. For example, clay-rich soil can retain moisture for several days, while sandy soil can dry out in 24–48 hours in hot weather.
• Root depth:Tomatoes develop a strong root system (over 30 cm deep)latelierpaysan.org, especially if encouraged. In loose, deep soil, roots can access water from deeper layers, making the plant more resilient to temporary droughts. In contrast, in compacted or shallow soil, water accumulates less (the surplus drains away or stagnates) and roots explore a reduced volume – the tomato then relies more on regular surface watering.
• Mulching and soil structure:The use of anorganic mulch(straw, mulch, etc.) reduces surface evaporation and maintains soil freshness, whichdecreases the frequency of watering. Similarly, well-structured soil (not compacted, rich in humus) retains water better. These agricultural practices influence water management as much as soil texture.
• Case of potted tomatoes: A substrate in a container or pot is akin to a very draining medium with low reserve. Potted tomatoes therefore requiremuch more frequent watering(sometimes daily in summer), as the limited volume of soil dries out quickly. It is recommended to incorporate compost or coconut fiber to improve retention and to avoid pots that are too small.

How much water to bring to your tomatoes?

• Approximate weekly needs:In open ground, it is often estimated that a tomato needs about20 to 30 mm of water per weekin summer (which is 20–30 L/m²/week) under normal conditions. This roughly corresponds to2 to 3 liters of water per plant per week(for ~2 plants/m²) in a temperate climate. Of course, this average figure must be adjusted according to the weather: in the case of a prolonged heatwave, the needs can double, while in cooler or rainier periods, the supply can be reduced or even nil.
• Use ETP to calculate irrigation:The most accurate method is to rely on the local ETP and the Kc coefficient of the tomato. For example, with a daily ETP of5 mmand a Kc of0.8(tomatoes in flowering stage), the needs are ~4 mm/day, which is4 L per m²aveyron-bio.fr. In a week without rain, that would be 28 L/m² to distribute. Conversely, if the ETP drops to 2 mm on a cloudy day, there is no need to provide more than 2 L/m² that day. Agricultural weather services often provide the daily ETP, which helps to adjust watering "just right."
• Signs of a good dosage:Ideally, each watering shouldmoisten the soil deeply.(20–30 cm) without clogging. A supply that is too low, which only wets the surface, leads to a shallow root system and increased dependence on water. Conversely, an excessive supply at once can leach nutrients and waste water. A rule of thumb in summer: about3 L per plantduring a heavy watering, which should soak the soil deeply; and repeat once or twice a week depending on the climate. With 2–3 well-spaced waterings, this reaches about ~6 L per plant/week (for a “normal” summer)., ce qui doit imbiber le sol en profondeur; et répéter une à deux fois par semaine selon le climat. Avec 2–3 arrosages bien répartis, on atteint ainsi les ~6 L par plant/semaine (pour un été “normal”). Monitor your plants: slightly drooping leaves at the end of the day indicate that it is time to water, while dark green leaves drooping down and waterlogged soil signal an excess of water.

How often to water tomatoes?

• General principle:It is better to waterless often but abundantlythan every day in small amounts, especially in open ground. Spaced waterings (e.g., 2 times a week) encourage the roots to explore deeply, making the plant more resilient in case of heat stress. However, during a heatwave on light soil, it may be necessary to water more often (every 2 days, or even daily) because the soil dries out very quickly.
• Adaptation to climate:In adry Mediterranean climate, watering will need to be more frequent (e.g., 2–3goodwaterings per week in summer, in addition to any dew or storms). In a climateoceanic or humid, weekly watering may be sufficient, especially if regular rains supplement the supply. A simple rule is to wait for the first signs of thirst to appear (softened foliage during the day) before watering, without allowing the plant to wilt significantly.
• Time of day:Thebest timeto water is early in themorning. Watering at dawn allows the water to penetrate well without too much evaporation, and the plants benefit from it to cope with transpiration during the hot hours. Watering in the evening is possible (especially in case of high heat during the day), but it leaves the foliage wet at night – which can promote downy mildew and other fungal diseases. Absolutely avoid watering in the full midday sun (wasting water due to maximum evaporation, and risk of thermal shock to the roots).
• Special cases: Young transplantedplants need frequent watering at first to ensure recovery (soil kept moist on the surface during the first weeks, often a light daily wateringis sufficient). suffit). Greenhouse tomatoes: the frequency of watering may be less than in the open field, as moisture is retained more (it is estimated that in a greenhouse the needs are ~20% lower than the outdoor ETPaveyron-bio.fr). Nevertheless, as the temperature in the greenhouse can be high, it is important to closely monitor the dryness of the substrate and ventilate to avoidwater stress..

The buzz about waterless tomatoes: myth or reality?

Test (not very conclusive) of waterless tomatoes

• Origin of the buzz:For a few years now, media reports have highlighted farmers who grow vegetables, including tomatoes,"without water". These spectacular announcements have made a buzz in the press and on YouTube, suggesting that one could obtain tomatoeswithout any watering..
• Clarification – "without water" vs withoutirrigation. :In reality,"without water" means without artificial irrigation.These producers rely on rain (random) to provide most of the moisture. In other words, their plants survive thanks to soil water and natural precipitation – not by magic without any water.
• Very low yields:The downside of growing without watering is asharp drop in yields.In the case of the famous farmer from Essonne, he stated that in nearly 30 years, he has managed"barely a dozen decent tomato seasons"– in other years, the harvest was meager or even nonexistent in the absence of irrigation. This choice comes with production losses of around-30% or moreduring dry summers.

"Personally, I don't think it's wise to use as an example an agricultural model where the operator can only earn a living one year out of three... In a context where 60% of farmers will be retired in 10 years, it's uncertain that we can motivate young people to take over with such economic prospects."

• Agronomic interest:These experiences have the merit of selecting tomato varieties that are more resistant to water scarcity, and of showing that a very lively soil (cover crops, thick mulching, etc.) can help plants endure significant water stress. It is true that a tomato with very deep roots can survive without irrigation by tapping into the residual water in the soil, and that a slightwater stresscan sometimes concentrate sugars in the fruit. However,no scientific study validates the idea that we can achieve normal yields "without water"in our climates. On the contrary, we invariably observe a decrease in the number and size of fruits under severe water deficit. Reports of the "superior" taste of unwatered tomatoes remain anecdotal: blind organoleptic analyses have not found a significant difference in flavor between moderately water-stressed tomatoes and well-irrigated tomatoes.
• Conclusion on this point:The"without irrigation"is mainly a philosophical choice. It isnota method that can be generalized for a productive vegetable garden, unless one is willing to accept very low yields. This reminds us that too much wateris like no water at all.are two extremes to avoid. Between these two poles, there are strategies forreasonable irrigationthat allow for water savings while maintaining satisfactory production.

"Water is precious, it is our duty to use it wisely. But "quality food" is just as important! And in my opinion, turning water into food is always a good calculation. (In parallel, building mega-reservoirs to irrigate corn in arid regions to feed pigs in Poland does not seem like the idea of the century to me) Once again, thenuancehere is of utmost importance."

Between two extremes, there are as many nuances as there are gardeners.

"Training" tomatoes to live without water: an appealing myth, a more complex biological reality.

It is often said that it would be possible to "train" tomatoes to live without water, simply by watering them less and less over the seasons. This idea, appealing during drought periods, is based on apart of biological truth, but it isgreatly simplified– and often misunderstood.

Yes, a plant can adapt... but within strict limits.

At the scaleof an individual, a tomato can indeed develop certainphysiological adaptationsin response to moderate water stress:

• slightly deeper rooting,
• faster closure of stomata,
• reduction of leaf surface,
• temporary modification of the growth/reproduction balance.

These adjustments allow the plant tosurvivea water deficit, sometimes producing a few fruits… butnot fully express its potential. These are mechanisms oftolerance, not a fundamental transformation of the plant.

Selection is not done on individuals, but on populations

A crucial point, often overlooked:

 One does not select a variety by “hardening” an isolated plant.

Genetic selection only works on:

• largepopulations,
• over several generations,
• by only keeping for reproduction the individuals that combinesurvival + satisfactory reproductionunder water stress.

A tomato plant that survives without water but produces almost nothingis not a good candidate for selection. Drought tolerance only makes agronomic sense if it remains compatible with a minimum yield.

Effective selection takes… time. A lot of time.

Even in professional breeding programs,improving drought tolerancetakes:

• decades,
• sometimescenturieson the scale of agricultural history.

The so-called "resistant" varieties have never become independent of water: they are simplya bit more efficient in its use, or capable of better withstanding periods of occasional stress.

Believing that a gardener can, in a few years, transform a tomato into a plant adapted to aridity is more of ainspiring storythan biological reality.

Epigenetics: real adaptations… but temporary

Certain practices can induceepigenetic modifications(different expression of certain genes without modification of DNA):

• repeated water stress,
• extreme environmental conditions,
• partial transmission over one or two generations.

But these effects are:

• unstable,
• reversible,
• strongly dependent on the environment.

A "hardened" tomato does not genetically become an arid environment plant.

It remains atropical origin plant, historically selected in contexts wherewater was not a permanent limiting factor.

A tomato will never be a cactus

This is perhaps the most important point to remember:

the tomato is not, and will never be, a xerophytic plant.

• It has a large leaf surface.
• It actively transpires to cool itself.
• Its physiology is optimized for environmentswarm but hydric available.

Comparing it to plants adapted to extreme drought (cacti, agave, certain legumes) is abiological category error.

In summary

Yes, we can:

• slightly improve thetolerance to water stress,
• select varietiesa little more water-efficient,
• work on soil and practices to reduce needs.

But no:

• we do not "reprogram" a tomato in a few seasons,
• we do not transform a tropical plant into a desert plant,
• and we do not eliminate the fundamental link betweenwater, photosynthesis, and yield.

Talking about "waterless" tomatoes without integrating these biological limits amounts toconfusing adaptation, survival, and production– three very different concepts.

Tips for effectiveandwater-saving watering

• Watering in the right place:Bring waterto the base of the plants, directly on the soil, not on the leaves. Watering the foliage is not only ineffective (water evaporates before reaching the roots), but also promotes diseases (fungi such as downy mildew on wet leaves). Use a long-spouted watering can, a hose with a drip attachment, or a localized irrigation system.
• Prefer drip irrigation:If possible, install adrip irrigation systemto slowly distribute water and avoid runoff. These systems can be equipped with timers to precisely adjust the duration and frequency of watering. 
• Mulching and shading:As mentioned earlier, maintaining athick mulcharound tomato plants is one of the most effective measures to retain soil moisture. An organic mulch of 5–10 cm (straw, hay, wood chips, dry clippings…) reduces evaporation andlimits the 'thirst shocks'by keeping the soil cool. In very arid climates, one can also provide lightshadingduring the hottest hours (shade cloth above the vegetable garden) to reduce local evapotranspiration.
• Monitor and adjust:Every garden is unique; therefore, it is necessary toobserveyour plants. Leaves curling inward or drooping during the day = sign of water shortage -> slightly increase watering. Pale yellow and soft leaves + waterlogged soil = too much water -> space out watering. The important thing is theregularity: tomatoes dislike fluctuations (alternating between dry and excess water). Watering should form a stable rhythm corresponding to the needs of the season. In case of absence, arrange for a neighbor to water or install backup systems to avoid sudden water stress.
• Do not wait for the foliage to wiltto water: Just as we do not wait until we are severely dehydrated to drink, the same goes for plants.The first signs of leaf wilting indicate a decrease in yield.
• Save water:Think aboutcollecting rainwater(tank, barrel) to water your tomatoes instead of using drinking water. Rainwater is also better for plants (no chlorine, ambient temperature). Adjust the amounts: there's no need to water heavily if a heavy downpour is forecast for the next day. In summer, focus watering on the most sensitive vegetables (tomatoes handle small stresses better than lettuce, for example). Finally, accepting to lose a bit of yield during severe drought is part of areasonable use of the resource: it's better to water a little less than to waste precious water, while maintaining enough supply to avoid jeopardizing the harvest.

Conclusion: the right balance for watering your tomatoes

Watering tomatoes “often” or “not often” does not have an absolute answer –it's all about balance. It is important toprovide sufficient waterto ensure healthy growth and quality fruits, while avoiding excess that leads to diseases and waste. Agronomic studies and experience show that with fine management (for example, relying on ETP, mulching, targeted inputs), one canreduce irrigation water by 20–30% withoutmajor loss of yield. Conversely, wanting to grow “tomatoes without water”“tomates sans eau”remains a risky bet, tolerable only on a small scale and with a significant drop in production.

In practice, a wise gardenerwaters "when necessary"rather thansystematically every day. This means observing the weather, the soil, and the plants:neither too much nor too little, and regularly. Taking into account the climate (sunlight, wind…), the nature of the soil, and the stage of your tomatoes, you will find theideal watering frequency. 

The key word isnuance: between overwatering and permanent water stress, there is a reasoned path that will allow you to harvest beautiful juicy tomatoes while respecting the water resource.