Tomato leaf curl is a common problem during the growing season and a sign that your plants are not happy. It is typically a physiological response to a lack of moisture, nutrients, or temperature, but sometimes can be caused by pests.
Gardeners want a smooth process when growing tomatoes, from sowing or planting to picking the ripe fruits at harvest time. Tomato leaves curling may send a shiver down the spine, but it does not mean it is time to panic. There are quick, simple changes you can make to keep your tomato plants happy.
Tomato leaf curl typically affects the oldest foliage first, and these affected leaves are best removed with sharp pruning tools (such as these Felco F2 pruning shears at Amazon) to keep the plant healthy. At the first sign of curling, consider it a call to action. Here we look at the four most common causes of tomato leaf curl, along with easy fixes to address the issue and preserve your tomato crop.
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1. Watering
(Image credit: Future/Jacky Hobbs)
Tomatoes prefer consistently moist soil throughout the season. A lack of water can cause plants to curl their foliage as they try to conserve moisture, especially during warmer periods. Drying out is especially risky when you grow tomatoes in pots.
At the other end of the scale, overwatering can also cause leaf curl. In addition to curling, yellowing tomato leaves is another tell-tale sign of excess moisture in the soil.
Consistency is key when watering tomatoes. This includes regularly checking the moisture levels and deep watering rather than a little-and-often approach.
One effective way to achieve this consistency is to use a soil moisture meter to check the moisture levels beneath the surface. A meter like this soil moisture meter on Amazon can provide quick readings to help you confidently determine when to water plants.
Such an approach ensures evenness and can help alleviate blossom-end rot affecting the fruits.
Mulching around plants is also a recommended method for retaining moisture in the soil and preventing it from drying out too quickly. The best materials for mulching tomato plants include bark, compost, or straw. You can get bags of pine bark mulch at Lowe’s.
2. Temperature
(Image credit: Future)
Tomatoes are known to thrive in warmth and sun. However, there can be too much of a good thing.
The plants get stressed when temperatures go over 90°F. This causes them to curl their leaves to conserve water. Reducing the surface area means less transpiration, as the plant tries to hold onto the moisture it has.
It can be an issue if you are growing tomatoes in warmer climates or plant them in a greenhouse that can heat up over summer.
In hotter climates, it can be beneficial to plant tomatoes in a spot that gets afternoon shade to protect them from the scorching temperatures. Or you can cover plants from intense sunlight with shade cloth, such as this 50% shade cloth at Amazon.
If you grow tomatoes in buckets, pots, or grow bags, move them out of direct sunlight during a heatwave to prevent leaves from curling.
Tomato leaf curl can also be caused by cold, too. If temperatures drop below 54°F, the leaves can curl inwards as a protective measure. To prevent this, don’t plant tomatoes outdoors too early. And always harden off plants to get them accustomed to outdoor temperatures.
If you are growing tomatoes in windy sites, giving them a protected spot is beneficial, as cold winds can scorch the edges of leaves and cause them to curl.
3. Nutrition
(Image credit: Future)
Tomatoes are hungry plants that require lots of nutrients to grow and produce fruit throughout the season. If they don’t get the essential nutrients they need, the leaves start to curl as a result.
Fertilizing tomatoes is a vital task for healthy plants and bumper yields. The trick is to start with a balanced fertilizer (such as this organic all-purpose plant food at Burpee) and switch to a feed higher in phosphorus and potassium (like this tomato booster at Walmart) once the plants start flowering.
You don’t want to give tomato plants too much nitrogen. Plants with an excess of nitrogen produce too much foliage, making it unsustainable for the plant to support all this lush growth. So the leaves curl.
Regular feeding avoids issues linked to a lack of certain nutrients. For example, a deficiency of potassium or phosphorus can result in stunted growth or curling leaves.
Use a liquid tomato feed once flowering begins and feed plants every two or three weeks until late summer. Such products are fast-acting and deliver nutrients quickly to plants, but need to be applied often to be most effective.
There are also opportunities to make your own tomato fertilizer, such as a comfrey tea or nettle feed.
4. Pest or Disease
(Image credit: Future)
Tomato leaf curl is often the result of environmental stress, but not always. Tomato pests can cause the issue, particularly aphids, whiteflies, thrips, spider mites, and broad mites, which all suck sap from leaves and stems.
Small sap-sucking summer pests like these can be squashed between your finger and thumb, removed from the plant with a jet of water, or sprayed with insecticidal soap (like this ready-to-use insecticidal soap at Walmart).
A way to avoid pest problems is to use tomato companion plants, which can repel pests or attract beneficial natural predators. The likes of marigolds or chives can deter many pests, while sweet alyssum and dill can draw in predators to feast on pests and protect your plants.
Pests also bring the risk of spreading tomato diseases. And leaf spot, mosaic virus, and tomato yellow leaf curl virus all have leaf curl among their symptoms. Unfortunately, such viral diseases need plants to be removed to prevent any spread.
It is advisable to look for disease-resistant tomato varieties when planning which types to grow to mitigate the potential risks during the season. For example, these ‘Bodacious’ tomato seeds from Burpee are disease-resistant and produce large, round fruits.
What to Shop
‘Supersweet 100’ Tomato Seeds
‘Supersweet 100’ is an indeterminate cherry tomato that is resistant to many diseases, including early blight, fusarium wilt. verticillium wilt, and tobacco mosaic virus.
Miracle-Gro Tomato Plant Food
This water-soluble tomato plant food can be applied when you water plants every 1-2 weeks for healthier plants and bigger tomatoes.
A set of small tomato cages made of premium steel with rust-resistant plastic coating to keep plants supported through the season.
FAQs
How Do You Tell if Tomatoes Are Overwatered?
When it comes to how much water tomato plants need, they generally need about an inch or two of water weekly. However, this can vary depending on the weather, rainfall, and whether the plants are in the ground, raised beds, or containers.
Overwatered tomato plants can wilt, droop, and have yellow leaves. In addition, the fruit can crack or split, and there may be green mold on the soil surface due to excess moisture.
Tomato leaves curling is frustrating, but so is a plant that flowers but doesn’t fruit. If your tomato plants are not fruiting, it is usually due to blossom drop, where the flowers fall before being pollinated.
Blossom-end drop can be caused by temperatures too high or too low. Or it can be due to a lack of pollinators. If you want to hand-pollinate plants to get fruit, you can move pollen with cotton swabs or a toothbrush, or try the tomato tapping trick and shake plants to distribute pollen from flower to flower
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