Why Are Tomato Plant Leaves Curling? 10 Tomato Leaf Curl Causes

Even when I spend a lot of time and energy on my vegetable garden, I often encounter some problems that I wasn’t expecting. This year, I came across some tomato plant leaves curling for the first time.

Walking around my garden, expecting to find a lush harvest of plump tomatoes, and discovering a plant with curled leaves is a disappointment, to say the least.

Let’s discover the causes of tomato leaf curl, a common tomato plant problem, and what to do about it if you find it in your garden!

Months of organizing, planting, and weeding have gone into my vegetable garden this year. 

My husband made me some raised garden beds, and I used them to transform a flower garden into a combined perennial and veggie garden.

Any early summer garden tour can give you some lovely surprises – like this oddball of a tomato plant.

I laugh every time I walk by this specimen. It is supposed to be a cherry tomato plant. The plant is about 8 inches tall and has a huge tomato on it in relation to the size of the plant. 

I’m a bit afraid to pick it for fear the plant will go into shock, losing such a big part of it. Baby tomato my foot!

Luckily for me, the leaves of this tomato plant seem to be in good shape. However, the same can’t be said about a smaller nearby plant which is suffering from leaf curl.

Fortunately, the curling on the leaves is not too significant and I see no signs of insects, but the tomato plant leaves curling do have me concerned. Since this is a relatively new plant, transplant shock is likely to be a factor here.

At the very least it shows me that the plant is under stress which is a common cause for tomato leaf curl.

What does a normal tomato leaf look like?

Healthy tomato plants have leaves that are a medium-green color but the shade can vary depending on the type grown. The leaves are softly fuzzed.

They should have no chewed edges, fuzzy mold, yellow edges, holes or black spots on them. The leaves should be open but may droop downward a bit.

If the leaves of your tomato plant don’t look like this description, but instead roll or curl upwards or downwards, like the image below, it is time to figure out why this is happening.

What is tomato leaf curl?

Tomato plants affected by tomato leaf curl (also called tomato leaf roll) have curled leaves that are distorted. The leaves often curl upwards and may be thick-looking. 

Sometimes the leaves are lush and green, and other times they display a yellowish color. The plant may be stunted and any fruits that it produces are small and likely to be misshapen.

If the curled leaves are caused by a virus, the condition can spread rapidly and really impact your tomato harvest.

Some varieties of tomato plants, such as “Big Boy”, “Floramerica”, and “Beefsteak”, seem to be susceptible to the condition. Unfortunately, these are types I often choose!

What causes tomato plant leaves curling?

Tomato leaf curl is a common problem and can be caused by many factors  – some easy to fix mistakes made by gardeners and other factors which are more problematic.

Some common causes are these:

• very hot temperatures – this also causes tomato sunscald
• watering issues – especially for tomatoes in pots
• over-fertilization
• transplant shock
• too much pruning

Additional causes, and ones that are more serious, are viral diseases called tomato leaf curl virus, tomato mosaic virus, and herbicide exposure.

Due to differences in the severity of the problem, depending on the cause, it is important to be sure about the reason for the leaf curl on your tomato plants before you try to treat it.

Let’s examine these causes of tomato leaves curling up of one by one.

Extremes in temperature can cause leaf roll

Leaf curl on tomato plants is made worse by hot weather and heat stress. You may notice that the lower leaves of your plants curl upwards in hot and dry conditions.

This is normal and not a huge cause of worry. As long as the situation does not go for too long it should not significantly reduce your crop of tomatoes.

Even though tomato plants love sunlight, and lots of it, when temperatures consistently stay above 85°F (29.44°C) the plant will face stress. This stress can even result in tomatoes refusing to turn red!

In hot and dry conditions such as this, tomato plants lose a lot of moisture due to evaporation. This causes the leaves to curl up.

Curled tomato leaves are the plant’s way of trying to control the lack of water since they absorb less sunlight and lose less water.

Affected plants normally keep their green color if heat is the cause of curling. Leaf curl caused by extremes of heat will often right themselves if the conditions improve.

Adding additional moisture really helps when the temperatures remain hot and dry. If you live in a place where the temperatures are often very hot for long periods of time,  your tomato plants are less likely to suffer from tomato leaf roll if the plants get some shade from the afternoon sun.

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Watering issues and drought 

Hand in hand with hot conditions is the problem of insufficient water for tomato plants. Incorrect watering is one of the main causes of tomato leaf roll as well as disorders such as catfacing.

Both under-watering and over-watering can cause leaf roll.

Watering tomatoes too little causes tomato leaves to curl up

Tomato plants are particularly finicky when it comes to their water needs. After all, the end result of a tomato plant is a luscious and juicy tomato, so it needs watering consistently, particularly when it is hot and dry.

Without this moisture, the leaves will curl up on the margins. With proper watering, you can often prevent leaf curl from happening.

Severe loss of moisture will make the problem worse and can lead to tomato plant leaves turning yellow, curling, and then dying.

Give tomato plants 1 inch of water a week either through rainfall, or additional watering. Manual watering should be given near the root zone with a hose, soaker host or drip irrigation. Avoid overhead watering which can cause fungal diseases in tomato plants.

Adding a 2-inch layer of organic leaf mulch around your tomato plants will limit loss of moisture and help prevent tomato leaf curl.

Watering tomatoes too much can result in tomato leaves curling downwards

Too much watering can also be a cause of leaf curl on tomato plants. Too much moisture can lead to root rot and cause the situation of tomato plant leaves drooping and curling downward instead of up.

Avoid watering too much, since this can also contribute to tomatoes splitting as well as leaf curling. Fluctuations in watering can also lead to tomato blossom drop and  blossom end rot, so consistency is the key.

If over-watering causes tomato leaves to curl, hold off on watering until the soil dries out before resuming. Normally, this situation will fix itself if you start to water properly. 

Be sure soil drainage is good since slow draining soil can be the cause of tomato plants retaining too much moisture.

Over-fertilization is likely to cause tomato plant leaves curling down

Tomato plants need nutrients in the form of a balanced fertilizer with a good mix of nitrogen, phosphorus, and potassium at initial planting time.

Once fruit production commences a fertilizer with phosphorus and potassium will help with flowering and fruit production. Too much nitrogen at this time can cause problems such as leaf curling.

The reason for this is that when there is an excess of nitrogen in the soil, the plant focuses on leaf production, rather than fruit production. The leaves may become thick, and green and will roll easily.

This problem generally will fix itself in time. Leaf curl of this type has little impact on your harvest or the plant’s health.

The best way to avoid this type of leaf curl is to avoid overfertilizing. Testing your soil with a soil test kit will tell you whether the soil is too rich in nitrogen for tomato plants.

If a lack of nutrients causes leaf curl, the leaves often curl downward instead of upwards, as they do in hot and dry conditions.

Another nutrient issue that can cause leaf curl is too much salt in the soil. In this case, the leaves turn yellow and roll.

Shock from transplanting tomatoes can cause tomato leaves to curl

Tomato plants are often grown from cuttings as well as from seed. when new seedlings are transplanted into your garden, the plant can undergo stress.

Tomato plants have fairly delicate root systems which can easily be damaged when the plant is moved from the nursery to your garden.

This stress can lead to leaf curl on tomato plants. Once again, this is a defense reaction on the part of the plant.

The leaves of tomato plants affected by this type of leaf curl are normally green but can look leathery and firm.

Tomato plants that develop leaf curl for this reason will normally recover quickly. Give them plenty of water as they get used to their new conditions.

Be sure to harden the plants to slowly let them get used to your garden and handle them gently when planting. Transplanting on a cool day, early in the morning is beneficial.

Row covers or tarps that temporarily block the sun are also helpful. Be sure to wait to transplant until daytime temperatures are consistently around 75° F (23.8 ° C) and night time temperatures don’t dip below about 65° (18.3 ° C)

Too much pruning may cause tomato leaf roll

Tomato plants often develop suckers at the leaf axils which are generally pruned away. Leaving them can make the plant unstable and hard to manage.

Removing the leaves on the lower part of a tomato plant can be useful too, and may keep the plant from developing soil-borne diseases. Late in the growing season,  it is wise to prune tomato plants to speed up the ripening of fruit.

However, while some pruning is beneficial and can benefit fruit development, too much of it can cause problems. If too much foliage is removed at one time, the plant will undergo stress and curl up the leaves in response.

Always water the plant well after pruning it to avoid this happening. The problem is usually short lived.

Weed killers can cause leaf curl

Many weed killers used on lawns near your vegetable garden can be the cause of your tomato plant having curling leaves. 2,4-D or dicamba and particularly problematic.

Even though the herbicides are not used in the vegetable garden, their drift, caused by wind, can be the cause of leaf curl. The herbicide drift might even come from a nearby yard!

Tomato plant leaves with this type of herbicide harm tend to bend downwards and twist around the stem. Individual leaves curl upward with a cup-like shape. This is different from the leaf curl of tomatoes caused by hot conditions or lack of moisture.

Other herbicide drift problems causing leaf curl occur when there is residue in the soil. This can come from contaminated compost, manure, or mulch. Be sure to get yours from a trusted supplier to avoid this.

There is no cure for herbicide-caused leaf curl. Some plants may recover and others will die. In the future, avoid using weed killers on lawns near edible plants.

Curly top virus in tomatoes

Another cause of tomato leaves curling upwards is the tomato curly top virus. In this virus, the smaller leaves at the top of the tomato plant grow in a wiry pattern and curl.

The leaves of infested plants have a purplish discoloration on the underside of the leaves which are crinkled and cupped upward. They may also be roughened.

This curly leaf tomato disease virus is transmitted by a beet leafhopper which feeds on the sap of infected plants and spreads the disease to other plants.

The curly top disease also affects potatoes, peppers, and eggplants.

Plants infected with this disease have stunted growth and small harvests. There is no cure for the virus. Remove infected plants to keep the virus from spreading.

Be on the lookout for beet leafhoppers, rotate crops, and take care to inspect new plants before adding to the garden.

Tomato yellow leaf curl virus

Curling leaves on a tomato plant could caused by a virus such as tomato yellow leaf curl virus, (spread by the silver leaf whitefly) or tomato mosaic virus (spread by aphids.) 

High temperatures and low humidity can make the problem worse. If your tomato plants become infected with the leaf curl virus when they are already suffering because of lack of moisture and nutrients, they are more susceptible to infection with the virus.

Tomato leaf curl disease symptoms are small leaves that become yellow between the veins, leaves curling upwards and towards the middle of the leaf, and shortened shoots.

The yield of infected tomato plants can be greatly impacted. Leaf curl virus spreads easily from one plant to another, so infected plants should be removed and disposed of.

If tomato leaf curl diseases are to blame for your problem, new growth will be affected, rather than the older leaves more normally affected by tough growing conditions.

There is no cure for the tomato leaf curl virus. Be especially on the lookout for whiteflies and aphids to avoid any chance of developing a leaf curl virus.

Insecticidal soaps are helpful in controlling aphids. Get a homemade recipe for insecticidal soap here.

In the future, choose varieties that offer resistance to viruses. 

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Some disease-resistant varieties are:

• Tycoon tomato
• Mochomo tomato
• Rally tomato
• Charger tomato
• Brenda tomato

Pests feeding on tomato plants cause leaf curling

There are several pests that love to munch on tomato plants. Whiteflies and aphids will cause the diseases mentioned above, but broad mites and pinworms can also infect plants and cause tomato leaves to curl.

Be sure to inspect plants often and remove any pests when they get out of control. Once removed, the leaf curl will normally rectify itself.

Companion planting is also helpful in avoiding pests in the tomato patch.  Nasturtiums, marigolds, basil, and chives are all helpful in repelling some pests.

Plant your companions a few weeks ahead of your tomato plants. They need to be quite large to do a good job of insect repelling.

To control tomato leaf curl, practice crop rotation, and other good gardening techniques. Be careful of pesticides, water properly, and choose resistant varieties of tomatoes.

Thankfully, most cases of curled leaves on tomato plants are harmful, so you will still be able to enjoy your harvest of delicious tomatoes!

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Admin note: this post about tomato plant leaves curling first appeared on the blog in June of 2014. I have updated the post to add much more information about leaf curl, a printable for your garden journal, and a video for you to enjoy.

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