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The Ultimate Guide to Correct Tomato Plant Watering


Guide to correctly watering tomato plants.

While there are many things that go into producing a perfectly ripe tomato, water is one of the most important variables.

The best way to water tomato plants at any stage is to keep the soil moist.  For seedlings, take extra care to not soak the soil, but don’t let the topsoil dry completely. For developing plants, water thoroughly and consistently to maintain moisture at least 6” deep at the root zone. As fruits ripen, back off on watering to encourage sugar production.

Luckily, tomatoes are water hogs, so it’s difficult to overwater them. However, this also means you must take extra care to make sure tomatoes get adequate water throughout the season, which could mean using extra irrigation equipment.

The Importance of Water for Tomato Plants

Proper watering is essential to maintain the plant’s health and the fruits’ yield and quality.  Tomato plants need specific watering routines to prevent rot, stave off diseases that develop from wet foliage, and maintain the fruit’s water content.  

Tomato Seedlings

Newly-germinated tomato seedlings are delicate. Watering should be carefully monitored at this stage, with consistent watering each morning. Young seedlings may succumb to root rot or damping off if they are overwatered, or if they are watered at night. 

When the seedlings develop their first set of true leaves, they may require extra water in the afternoon as the root system expands. At this stage, it is difficult to overwater because the plant is growing so quickly. 

Once you begin hardening off your seedlings, give them extra water as needed to help them adjust to direct sunlight.

Tomato Fruits

More than 90% of a tomato’s fruit is water (sourceOpens in a new tab.).  Much like watermelons, water directly affects the size, yield, and quality of the fruit. Inconsistent or poor irrigation habits could not only result in lesser-quality fruit, but could lead to multiple diseases like blossom-end rot. 

Tomato plants need consistent, thorough watering as they grow, blossom, and produce fruit. However, once the fruits enter the breaker stage, where the color begins to change, they are entirely dependent on the existing water content within the fruit. Therefore, watering before this stage is extremely important to encourage healthy, juicy fruit development.

It is also the stage in which calcium is transported to the fruit through the roots via water.  If this does not happen properly, the fruits can develop blossom-end rot. 

Tomato Roots

Proper spacing is important to ensure each plant has access to sufficient water. If plants are placed too close together, or if the tomato patch is overrun by weeds, the roots won’t be able to soak up enough water to support fruit production.  

Healthy soil is an important part of proper irrigation..  Compacted soil can prevent water from moving through the soil, which can result in underwatering in dry climates, and overwatering in wet climates. Sandy soil may drain too easily, making it difficult for roots to soak up enough water to support new growth.

Compost and mulch can help improve poor soil structures.

The Basics of Watering Tomatoes

Besides melons, tomatoes are the most water-hungry plants you can grow in your garden. However, that doesn’t mean you should flood the veggie patch. A well-designed irrigation plan will maintain healthy fruit development without encouraging moisture-related pathogens.

Watering Tomato Seedlings

If you are starting your seeds indoors, you should plant them 6-8 weeks before the average last frost date. Seeds at this stage need to be kept moist but not heavily saturated.  Overwatering your seeds could inhibit root growth and encourage mold at this delicate stage.  

If the topsoil is close to drying out, water just enough to keep the tomato seeds damp. Consider using warm (but not hot) water at this stage, to encourage germination and help prevent damping off (fungi/mold that sometimes affects seedlings) (sourcOpens in a new tab.eOpens in a new tab.). 

When the seeds germinate, shift your focus from keeping the top of the soil moist to keeping the root zone moist. Water each morning until water runs out the bottom of the seed tray. 

It’s fine if the top of the soil dries out, but if the seedlings begin to wilt, don’t hesitate to water them. It’s important to support the growing root system and prevent unnecessary stress.

Watering Tomato Transplants

From this point on, take care to water the plants at the root zone as much as possible.  When tomato plant leaves get wet, they become susceptible to diseases like the following:

  • Leaf mold (yellow and black spots on the leaves and can spread to the fruit)
  • Septoria leaf spot (gray, water-soaked leaf spots that can spread to the flowers)
  • Bacterial spot (tiny black spots on the leaves that can spread to black spots on the fruit)

(sourceOpens in a new tab.)

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You can help prevent these diseases by keeping the foliage dry and only watering at the roots.  

Before the plant flowers, the water should penetrate through at least 6 inches of the soil.  This depends on the soil composition.  Lighter, sandier soils should stay moist at least 10 inches deep, while heavier soils should retain moisture at least 6 inches deep.  An inch of rainfall or watering will achieve these depths. 

Water whenever the top 1” of soil dries out. Water in the morning. In hot or dry climates, you may have to water again in the afternoon, or leave a soaker hose around the base of the plant through mid afternoon to prevent drought stress.

Watering Mature Tomato Plants

Continue to keep watering at the base of the plant in the morning, and remember that consistent, thorough watering 2-3 times per week is preferable. Shallow watering will stimulate shallow roots, which will not support the growing plant or fruit production.

After the plant flowers, begin watering to a depth of 12”-18”. A few inches of mulch around the plant can help with water retention. Drip irrigation systems and soaker hoses are the best watering techniques to ensure these conditions.  

Overwatered tomato plants will produce an abundance of foliage, but it may reduce the number of blooms.  If your plants aren’t blooming as much as they should, try to back off on the watering for a few weeks to see if it encourages flowers. Flowering can be a direct response to stress, so inducing mild drought stress may encourage a flush of new flower buds.

At this stage in the plant’s life, blossom-end rot can develop if the plant is not watered properly. Blossom-end rot is a calcium deficiency that manifests as black, water-soaked spots where the fruit meets the blossom.  Calcium is transported to the fruit through the roots, which can only happen if the roots stay consistently moist.  To combat this common disease, incorporate crushed eggshells into the soil and stick to a consistent, thorough watering routine.  

Watering During Tomato Production

Continue to water 2-3 times per week while the plant is blooming and as fruits begin to form.  

Since tomatoes can ripen off the vine, they do not depend on the plant once they begin the ripening stage.  

Once fruits begin to change color, back off on watering. This doesn’t mean to begin shallow watering, rather, water just as thoroughly, but less often. At this point, you are watering to keep the plant healthy, which is especially important if your plant is indeterminate.  If the plant is under-watered, it may not be able to support the weight of the fruit, and the fruit could fall off the vine and be eaten by bugs or begin to rot.

See our Simple Guide to Ripening Tomatoes (On or Off The Vine)

Tools & Methods for Watering Tomatoes

Once your tomato plants are established in the ground, the best way to water them is to use soaker hoses or drip irrigation systems. These keep the plant foliage dry and are water-efficient, and their use is often legally exempt from water restrictions, even in droughts (sourceOpens in a new tab.).   

Drip Irrigation

Drip irrigation systems are becoming popular choices for home gardeners.  The systems allow for even, consistent soil dampening and are great for introducing fertilizer directly to the roots.  For tomato plants, drip irrigation systems eliminate the risks attached to wet foliage.  Other advantages include: 

  • Less water waste
  • Fewer weeds (water only goes where it’s needed)
  • Systems are available at most hardware stores and are easy to install
  • Gardeners do not need to physically water plants
  • You can incorporate timers for consistent, reliable irrigation

Soaker Hoses

Soaker hoses are similar to drip hoses, except the water seeps out along the entire length of the hose, and it doesn’t require any special attachments..  Soaker hoses attach to regular garden hoses and can be moved to any area in the garden. 

The downside to soaker hoses is that the water weeps along the length of the hose, instead of specific points like a drip system. This can encourage weed growth between plants along the hose. However, soaker hoses have fewer problems than a drip system, and they are cheaper and easier to install.

For more information on how to use a soaker hose, visit this video at the University of ConnecticutOpens in a new tab. extension. 

Sprinklers

If soaker hoses and drip irrigation systems are not feasible for your garden, regular sprinklers will work, although they are less efficient and carry greater risk. If you choose to use a sprinkler, use it in the morning.  This will lessen (but not eliminate) the risks associated with wet foliage by allowing time for the sun to dry the plant. 

To assess how much water you will need for your tomato plants, place two cans between 1 and 2 feet away from your sprinkler system and turn it on.  Time how long it takes for the can to fill with 1-2 inches of water.  Keep your sprinkler on your tomato plants for this amount of time each time you water (sourceOpens in a new tab.). 

Hand Watering

If you use a regular hose, make sure to keep the water flow slow and at the root of the plant.  This will take patience, as you need to ensure you take enough time to saturate the soil at a sufficient depth without washing away the soil or drowning the plant.  

Your tomatoes’ quality and health is largely dependent on a watering routine that keeps the soil consistently moist.  Along with a healthy irrigation schedule, build up your garden soil with compost, and use mulch to prevent excessive evaporation.

Once you have an abundance of green fruits, it’s time to start thinking about the ripening process. Check out our article on the best ways to ripen tomatoes.

Sydney Bosque

Sydney has over 15 years of experience in lawn maintenance, landscape design, and organic gardening. She has an A.A.S. in Landscape Design/Organic Produce Production from the Nebraska College of Technical Agriculture.

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