7 Signs You’re Underwatering Your Tomatoes

Underwatering your tomatoes can cause wilting, lack of flowers, or stunted growth. Gardening expert Madison Moulton shares seven signs you may be underwatering your tomatoes and what to do about it.

Written by Madison Moulton Last updated: September 21, 2023 | 5 min read

In a sunlit garden, wilting tomato plants display a striking mix of vivid orange and lush green tomatoes, nestled amidst sturdy, verdant stems. Some leaves are wilted, curled and drooping, signaling water stress.

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Tomatoes are often one of the first plants new gardeners look to when starting their edible gardens. They are generally considered beginner-friendly and, as an added bonus, are incredibly versatile in the kitchen. Unfortunately, that doesn’t mean growing tomatoes is a problem-free activity. Incorrect care, particularly underwatering, can lead to a range of issues that jeopardize your summer harvest.

From wilting to yellow leaves and blossom drop, these are signs you may be underwatering your tomatoes. Make the necessary adjustments to your watering routine to bring your plant back to good health.

Wilting

The first sign of underwatering to watch out for is consistent across many plants – wilting.

Slight midday wilting, especially when temperatures are high and the sun is intense, is expected. But if your tomato leaves are still wilting the following morning, you’re likely underwatering.

Plant cells are largely made up of water, just like human cells. This moisture serves many purposes, but the plant’s structure is the one to look at when it comes to wilting.

When cells lack moisture, they lose their structure and the ability to hold the plant strong and upright. The leaves will begin to dry out and crisp up, signaling a watering issue.

A day or two of wilt is easy to fix. Once you’ve watered slowly and deeply, the roots will begin to draw up the moisture and slowly return to normal. If you wait too long, you may see more troubling signs.

Weak Stems

A tomato plant stands with feeble stems that quiver, unable to bear the weight of its plump, crimson treasures. It relies on stout yellow stakes for support, contrasting starkly with its weakened appearance. — When damaged, stems become more vulnerable to pest and disease infestations.

Since tomato leaves are thin, they don’t retain much moisture and can wilt quickly. Stems hold much more water, transporting it to parts of the plant that need it. When these thick structures droop and weaken, your tomato is seriously dehydrated.

Tomato stems become weak for the same reason leaves wilt – the cells cannot maintain the upright plant structure. Weak stems can easily snap, especially under the weight of heavy fruits, impacting your harvesting for the rest of the season.

Weak stems also pose a disease and pest problem. Damaged areas are far more prone to pest and disease damage, potentially spreading to healthy parts of the plant if not controlled. This is even more likely if the drooping has left stems in contact with the ground, where pests can easily access them.

Watering will resolve the issue within a day or two. However, if any stems have snapped, it’s best to remove those. They will only draw energy away from the plant that could be used to produce healthy growth and delicious fruits.

Yellow Leaves

A close-up of tomato leaves displaying a pale, yellow hue, evidence of their struggle for water. The foliage crinkles and curls, signaling distress amidst the parched earth. — One prevalent cause of tomato plant leaves turning yellow is insufficient watering.

Yellowing leaves are a tough plant problem to diagnose. Many stressors can cause leaves to turn yellow, from changes in environmental conditions to nutrient issues. But one of the most common reasons for yellowing leaves in tomato plants is underwatering.

Tomato roots draw up nutrients from the soil through water. When there is no water to transport nutrients, the plant shows signs of deficiencies like yellowing leaves. The yellowing will be patchy, indicating a lack of chlorophyll. These leaves won’t turn green again and will likely fall off the plant.

Lack of moisture for long periods can also cause older leaves to die off quicker than usual. You’ll notice lower and older leaves on the plant turning completely yellow before dropping off. Although this isn’t always cause for concern, several leaves dropping at once indicate an issue.

After watering deeply, adjust your watering schedule to avoid more leaves yellowing. Trim off leaves that are almost entirely yellow, as they won’t turn green again.

Lack of Flowers

A tomato plant exhibits a curious lack of blossoms, with only one small, green tomato taking shape amidst the sea of leaves and stems. The plant's struggle for growth is evident in its solitary fruit. — Consistently watering your tomato plant is crucial, especially when it starts flowering.

A strong tomato harvest relies on plenty of blossoms to turn into fruits. Without flowers, your tomato plant essentially becomes ornamental. However, producing flowers requires a lot of effort and resources, particularly when it comes to watering.

A consistent schedule is always important to avoid underwatering your tomatoes, but it becomes even more vital when your tomato begins flowering. If the plant doesn’t have enough moisture to sustain itself, it won’t have the resources required to push out flowers. The few flowers that appear may be diminished, unable to support later fruits.

There are many other reasons for the lack of flowers, from low light levels to inadequate nutrients. But underwatering is the likely answer if you’re a forgetful waterer and notice the soil is dry along with a lack of blooms.

Watering immediately won’t make blooms appear the following day, but it will help reduce stress and will eventually allow new flowers to pop up. If you struggle with watering consistently, consider installing a drip irrigation system to prevent issues in the future.

Blossom Drop

Delicate yellow blossoms on the tomato plant's branches catch the eye. These blossoms hold the promise of future tomatoes, embodying the plant's potential for growth. — To address blossom drop, monitoring soil conditions and watching for other signs is essential.

Even if your tomato plant is packed with flowers, it’s still essential to maintain consistent moisture in the soil. Frequent underwatering during the flowering stage can lead to a frustrating issue known as blossom drop, ruining your potential harvest for the season.

Blossom drop is an unfortunately common problem caused by several stressors. Sudden and unexpected dips in temperature, incorrect fertilizing, or even a lack of pollination can cause seemingly happy blooms to fall off your tomato plant.

Underwatering is a prominent cause of blossom drop. The lack of moisture results in stress that causes the plant to ditch excess flowers to conserve resources and stay alive. Needless to say, those flowers won’t come back once they’ve fallen off.

Since there are many causes of blossom drop, it’s best to investigate the soil conditions and look for other symptoms. If the soil is excessively dry and the plant is wilting, water immediately to stop more flowers from falling off.

Stunted Growth

Nestled against a weathered cement wall, a tomato plant bears green tomatoes, their promise of ripeness in the making. The robust leaves and stems contrast with the plant's stunted growth, hinting at untapped potential. — Frequent shallow watering won’t adequately hydrate thirsty tomato plants.

All plants need water to grow and survive. An underwatered tomato won’t be able to produce new leaves, extend their stems, or develop new flowers. Their growth becomes stunted.

Lack of growth is tougher to diagnose. When your tomato plant frequently puts out new leaves and stretches stems in its early growth stages, stunted growth is easier to spot than later in the season once the plants mature.

It’s also important to distinguish between determinate and indeterminate tomato types. Determinate tomatoes grow to a certain height, while indeterminate vines grow throughout the season. Mature determinate tomatoes won’t get any taller, but they should still produce flowers and fruits. If not, you may have an underwatering problem.

When watering, do so slowly and deeply to avoid stunted growth. Tomatoes have deep root systems that stretch far into the soil. Shallow watering isn’t enough to satisfy them, so the moisture may not reach all the roots, even if you’re watering frequently.

Compacted Soil

A tomato plant, set against dark, nurturing soil, appears weak and drooping. Its leaves, once vibrant green, have darkened, signaling distress. Wooden supports cradle the plant, offering a lifeline to recovery. — Compacted soil not only signals inadequate watering but also aggravates the issue.

The final sign is not in the plant itself but in the soil it is planted in. If you haven’t watered in a while, especially during the peak of summer when sunlight is intense, the soil will quickly become dry and compacted. This, along with other symptoms, indicates a watering routine problem.

Compacted soil is not only a sign of underwatering, but the condition also exacerbates the problem. Dry soil restricts airflow around the roots and may become hydrophobic, repelling water when your tomatoes need it most.

Resolving excessively dry soil requires patience. Start by watering slowly, ensuring as much water is being absorbed as possible. If the moisture starts to pool, wait for it to settle in and continue watering to reach the lower layers of soil.

If compacted soil is a regular issue, amend your soil with some nutrient-rich compost to break up the finer, easier-to-compact soil and improve drainage.

Final Thoughts

Underwatering tomato plants is not ideal, but it’s also not the end of the world. Prevention is your best defense, involving consistent watering and regular soil checks to grow healthy tomatoes.