Why are my tomato plant leaves curling up

Tomatoes are one of my garden must haves every year. I plant beefsteak, romas, cherries, and occasionally an heirloom variety that is oh so delicious. With all the joy of growing your own tomatoes, there is nothing more frustrating than seeing your plants in a state of distress. Leaf curling is often the first sign that something is amiss with tomato plants.

The good news is that, most of the time, leaf curl in tomatoes is easily remedied. There are, of course, a few cases where its a sign of something more serious. But serious tomato plant problems are usually a bit more rare than some of the most common leaf curling ailments.

The best way to stay on top off issues big or small is to make sure you spend time in your garden each day. This way, you’ll notice problems while they’re still small and manageable! Let’s take a look at the most common reasons a tomato plant’s leaves may be curling, and how to fix it!

Tomato Leaf Curling Causes & Fixes

Let’s dive into the reasons why your tomatoes may be struggling with leaf curl this year. There are a number of causes. Some are relatively benign and work themselves out, while others are unrecoverable. Here are 8 reasons your tomato leaves may be curling and how you can address them.

Under or Over Watering

Incorrect watering is probably the most common reason for tomato leaf curl and problems with your tomato plants in general. Even though tomatoes are considered to be fairly easy to grow, they’re pretty fussy when it comes to getting the right amount of water.

Too little and the plant won’t thrive; too much and you’ll damage the roots, which causes the plant to not thrive. You get the idea… When it comes to watering, we truly are looking for a ‘goldilocks’ situation.

A general baseline is about 2” of water a week for a plant in the ground (more if your tomatoes are planted in containers). But environmental factors like wind, heat, humidity and soil type can all play a role in adjusting that number up or down.

You can use a water gauge if you want to be exact.  Or, consider planting an ‘indicator plant’ nearby. Impatiens make a great indicator plant – especially if they are well shaded by your growing tomatoes – since they will immediately wilt when they have too little water. If your impatiens need water, your tomatoes likely do as well!

If you’re dealing with an overwatering situation, you’ll likely notice that your tomato leaves are curling under rather than upward. This could be a sign of root rot. Let the soil dry out for a few days to see if your plant recovers. If you’re paying attention to the health of your plant on a daily basis, you should be able to catch this fairly early.

Let’s look at how to water your tomato plants correctly to fix this potential leaf curling problem.

Water slowly and deeply. Most plants don’t like a deluge of water and tomatoes are no different. Think about the difference between taking a nice sip of water from a glass vs someone opening a fire hydrant for you. In an ideal situation, you can set up a drip system before planting. This will deliver water to your plants in a consistent and manageable way. If you don’t have a drip installed, don’t worry. You can simply turn your hose on the lowest setting and just let it slowly stream into the soil.

Water regularly. There isn’t really a hard and fast rule to how often you should water your tomatoes. A lot depends on how hot it is, if you’ve received rain recently, and where the plant is in its growth cycle. A good rule of thumb is to water every 2-3 days during the summer months (more frequently in containers). Once the fruit is set, you can pare this back to 1-2 times per week.

Water the roots, not the leaves. A common mistake with new gardeners is to water the top of the plant rather than the soil underneath. This can actually cause a lot of problems with your tomatoes including the spread of fungal disease (caused from wet soil splashing on the underside of the lower leaves), leaf burn, and attracting pests.

Environmental Stress

Environments with excessive heat, sun and wind are the most common sources of stress outside of watering. I have personally had issues with wind stress in my younger plants, but it can happen at any stage of your tomato’s lifecycle. 

Think of tomato leaves like small solar panels collecting sun to power the plant’s growth. If the plant has received too much sun and “is full”, the leaves may curl slightly for the remainder of the day. If this is the source of your leaf curl, don’t worry because they will revert to normal once evening arrives.

The same thing can occur with too much heat. We typically associate tomatoes as sun loving summer vegetables, but there is such a thing as too hot. Once temperatures reach 85 degrees during the day, your tomatoes will feel some stress.

This is the time of the season when new flowers stop developing and a lot of fruit begins to set. Your tomato leaves may curl up during the day, but as long as night time temperatures are cooler, they should recover. If excessive heat is sustained, the leaves can curl up, turn brown, and die.

Excessive wind can also be a huge source of environmental stress for your tomatoes. In Virginia, we get pretty strong winds throughout the spring. This can be especially difficult for young plants to deal with and you may see aggressive leaf curl that does not remedy itself.

It’s not the end of the world for your tomatoes, but it can impact plant growth and fruit production since the plant isn’t receiving the proper amount of sun through those curled leaves.

One of the most important things you can do to remedy environmental stress is to know what types of vegetables grow well in your region. If you live in an extremely hot, windy environment (or conversely in a very cold, wet environment), tomatoes may not be the best choice for your garden unless you can build in protection from the elements. But for most of us, excessive heat and sun are just part of the yearly summer challenge, and there are mitigation measures we can put in place to help.

• Install shade covers or position containers to avoid the hottest part of the afternoon. There are several ways to protect your plants from too much sun or heat. If your tomatoes are planted in the ground or in a raised bed, you can install shade cloth to cover your plants during the hottest part of the day. The easiest way of doing this is to drape the cloth over your existing tomato cages/stakes. You can remove it after temperatures have fallen out of the danger zone.
• Proper staking and use of tomato cages. Tying your tomatoes to sturdy stakes and cages is really important to the plant’s success. You’ll want to attach ties to multiple parts of the main stem as well as any larger heavy branches. Determinant tomatoes are a little easier to plan for since their growth is more compact. You have to get a little creative with indeterminate varieties as they continue to grow and grow throughout the season. For younger plants, make sure you harden off your seedlings before planting and give them as much protection from direct winds as possible.

Over Pruning

Pruning is another goldilocks area with tomatoes. It stresses out your plant, but it’s essential for keeping it healthy and growing efficiently (although there are some gardeners who firmly believe pruning of any kind does more harm than good).

No matter which side of the pruning debate you fall on, everyone agrees that excessive pruning is a bad idea. It can cause a number of problems – yellowing leaves, stunted growth, and a decrease in fruit production – with your plant including leaf curl.

Determinate tomatoes should not be pruned at all once the first flower appears. Doing so will impede growth and cause you to have a much smaller harvest of tomatoes. If you are going to prune at all, focus only on the very lowest branches that have leaves touching the soil. Leaf contact with the soil – either directly or through water splashing back on the underside of the leaves – can cause a number of fungal diseases.

Indeterminate tomatoes benefit greatly from gentle pruning throughout its growth cycle. You’ve probably heard of pinching off suckers… This is simply the removal of new growth between the primary and lateral stems of your tomato. This forces your tomato plant to put its energy into the main growth lines rather than creating a lot of branches that won’t ever produce fruit. Indeterminate varieties will also benefit from the removal of the lower branches to improve air circulation and prevent splash back.

Transplant Shock

If you notice leaf curl in a recently transplanted tomato, the cause is likely transplant shock. Tomatoes have fairly delicate roots and they can be easily damaged when moved into a new location. A lot of new gardeners think they are supposed to ‘break up the roots’ to encourage vigorous growth.

This doesn’t work for tomatoes. Even the slightest break or nick in the root ball can result in root damage. You’ll notice wilting, yellowing leaves, and – of course – leaf curl if this has happened.

The good news is that mild transplant shock is pretty harmless to the plant and it should recover with a little patience. Make sure that you don’t introduce any other form of stress – pruning, poor watering habits, etc – during this time or your plant may not recover.

Be gentle when transplanting. Tomato roots are very sensitive so be as gentle as you can when transplanting. Give the nursery pot a light squeeze to loosen the soil and then carefully extract the plant by pulling on the lower stem. Don’t touch the roots. Instead, place the entire root ball and lower part of the stem under the soil line. Gently fill in with soil, press down with your fingers, and water thoroughly.

Be patient. If you notice that your young tomato has already had transplant shock, baby it a little and allow the plant time to sort itself out. Avoid introducing any additional forms of stress to your plant until it recovers.

Excessive Nitrogen

Choosing the correct fertilizer for different stages of tomato growth deserves an entire article on its own. The best fertilizers for tomatoes have macronutrients like nitrogen, phosphorus, and potassium, and micronutrients like magnesium, calcium,and zinc.

If you’re new to gardening, thinking about multiple types of fertilizers for different growth stages of your tomatoes probably sounds daunting. It can be in the beginning, but the more you learn each year, the better your tomato crop will be in the next!

Here’s a little cheat sheet on the macros you find in fertilizer:

• Nitrogen. Promotes foliage growth.
• Phosphorus. Crucial for the growth and development of roots as well as fruit.
• Potassium. Helps the plant grow rapidly and produce flowers and fruit.

You can see from this list that your tomatoes need certain macros more at various stages of growth. There is sadly no single tomato fertilizer that works best for all gardens at all stages of growth. Let’s take a look at what happens when you introduce too much nitrogen to your tomatoes for too long.

When first planting your tomatoes, a balanced (or close to balanced) fertilizer is the ideal choice. But once the plant has reached maturity, starts flowering, and producing fruit, a fertilizer higher in phosphorus and potassium is recommended. Too much nitrogen at this stage will cause your plant to be overly bushy and can cause leaves to curl. Here’s why.

During the growth phase, if there is excessive nitrogen in your soil, the tomato plant will focus on leaf production. This can cause the plant to be overly bushy, but won’t cause any real problems.

Once the plant produces fruit, however, it doesn’t really know what to do with the extra nitrogen… As a result, the continued absorption of leaf-focused macronutrients causes leaves to become very dark green, thickened, and rolled.

Problems with excessive nitrogen typically resolve over time if you just stop adding fertilizer. Leaf curl from this problem has little impact on the plant or fruit yield; it’s really just kind of ugly to look at. The best way to help your tomatoes in this case is simply education.

Take the time (even if it’s over several seasons) to learn about what your plants need at different stages of growth. Soon, your tomatoes will be the envy of the entire neighborhood!

Disease

There are a number of diseases that can cause your tomato leaves to curl. We’ll talk about 2 of the most common in this section. Note that viral infections in your plants are rarely treatable and the plant is usually a total loss by the time you see the external symptoms. Once you have identified that your tomato plant is suffering from a virus, remove it from your garden immediately and dispose of it. Do not compost!

Curly Top Virus

If you notice that the leaves of your tomato plant thicken, twist and curl up, and become yellow with purplish veins, you are likely dealing with curly top virus. Curly top virus is a destructive plant disease that can affect more than 300 plant species including tomatoes.

It is passed from leafhoppers that have fed on a previously infected plant. A single leafhopper can start to infect other plants after only 6 hours of virus incubation in hot weather.

The effects of the virus are pretty serious and can range from stunted plant growth, deformed or wrinkly fruit, and fruit that tastes ‘off’. The leaf curl and discoloration will be your first indicator of curly leaf virus. Seeing your much anticipated tomatoes drop early or become deformed is devastating. Let’s look at how to fix this problem.

There is unfortunately no organic or chemical method to treat a plant infected with the virus and insecticides are ineffective against leafhoppers. If your plant is already infected, the best thing to do is pull it up and throw it away.

Prevention is, by far, the most effective treatment against curly leaf virus. The first thing is to ensure you plant healthy seedlings. Growing tomatoes from seed is very easy and incredibly rewarding. If you prefer buying plants, shoot for your local nursery. They typically have established relationships with growers and can vouch for the health of your plant. This isn’t always the case at big box stores.

Extensive weeding in and around your garden – especially Russian thistle and mustard weed – can help control the population of leafhoppers. They will overwinter in cozy, overgrown, weedy areas, so removing this environment is a great step in the right direction.

The most surefire way to protect your tomatoes from leafhoppers is to cover them with fine mesh or netting. This will create a physical barrier that will deter the insects from feeding on your plants and infecting them with the virus. This can be done more easily with determinate tomatoes or with indeterminates that you have topped.

Tomato Yellow Leaf Curl Virus

Tomato yellow leaf curl virus sounds just how it looks – the leaves turn yellow at the edges and curl upward. Unlike stress-related leaf curl where the leaf rolls completely inward, leaves affected by this virus almost look like they form a shallow bowl.

You may also notice spotted patterns on the leaves and a slight browning on the inside of fruits. The disease is spread by whiteflies that can carry it to all your tomato plants and other nightshades in your garden.

Tomato yellow leaf curl virus will severely stunt the growth of your tomato plants and will dramatically lessen the amount of fruit production.

Just like curly leaf virus, there is no treatment for a plant affected by tomato yellow leaf curl virus. The best thing you can do is to dispose of the plant and treat for whiteflies. Introduce predatory insects like ladybugs and spray a hard stream of water directly on the undersides of leaves to remove the whiteflies. If you’re dealing with a large infestation, horticultural oil can be used to suffocate whiteflies at any stage of their life. Repeat this weekly.

Pests

There are a number of pests that love to feast on tomato plants. Damage from pests that results in leaf curl will typically originate from sap suckers – aphids, broad mites, whiteflies, pinworms, etc. These pests are part of any healthy ecosystem and only become problematic when infestations get out of control.

Let’s talk about ways of keeping the sap-sucking pest population down.

As with most of the causes of leaf curl in this article, the key to avoiding a pest infestation is prevention. Creating an environment of biodiversity will encourage predatory insects like ladybugs, lacewings, parasitic wasps, and spiders to take up residence in your garden. They love to feast on the bugs that love to feast on your tomatoes! Invite them in and let them do the heavy lifting.

Companion planting can also be helpful in the war against pests. Plants like nasturtiums, marigolds, basil, and chives can help deter some pests and ‘trap’ others. Aphids, for example, will collect and feed on mature nasturtiums before ever noticing your young tomato plants. If you choose to give companion planting with your tomato plants a try this year, make sure you plant these herbs and flowers several weeks ahead of your tomatoes. They need to be large enough to make enough of a difference.

Manually removing pests is another effective – but time consuming – way of overcoming an infestation. Pests like aphids and whiteflies are pretty easily knocked off stems and the underside of leaves with a hard stream of water. Broad mites are small enough that you can simply remove infested leaves if you catch the problem early enough. The key is to be in your garden daily so you can notice a problem before it becomes an emergency.

If all else fails and you cannot keep the pest population down, you may have to remove the infected plant. If this happens, completely dispose of it and do not compost.

Herbicide Damage or Drift

Tomato plants are incredibly sensitive to herbicides and they can sadly come into contact with your plants even if you don’t spray them. Aminopyralid and Clopyralid are the most common types of herbicides doing the damage. They are chemical weed killers that target broadleaf weeds grown in grain fields, hay fields, and along roadways.

They are quickly absorbed by plants and remain chemically intact even once the plant dies. If a horse, cow, or chicken eats hay or grain from a producer who has used these chemicals, the herbicide passes right through the digestive tract unharmed. It then moves into new soil through manure, or into compostable material that is then shipped to your garden.

The bottom line is that your garden can experience herbicide drift (contamination from commercial spraying) or herbicide residue (contamination from feed or compost) through chemicals born on the wind, in grain for your chickens, or in the ‘organic’ compost you received from a local farmer.

It’s not super common to have this happen, but certainly something to watch out for if your tomatoes and other vegetables are struggling and you can’t determine another cause.

The only good news with herbicide damage is that it’s rare and is fairly easy to Identify. The leaf curl resulting from this looks quite different from other natural stress factors (where the leaves usually roll inwards).

When exposed to herbicides, tomato leaves tend to curl downwards and twist quite dramatically around the stem. You will see this first in new leaf growth, but eventually other leaves will start to twist as well.

Unfortunately, there is no way to recover leaves or branches of your tomatoes that have been damaged in this way. If the damage is mild, new growth may be unaffected, but the yield of your plant will still be impacted. If the exposure is severe, you will be better off pulling the plant immediately since it will not recover.

Unsurprisingly, this section will be about herbicide drift prevention rather than fixing the problem once you’ve identified it.

If you live in an area where commercial herbicides are being sprayed, you can try a few things. First, politely ask the neighboring farms if they use Aminopyralid and Clopyralid in their sprays. If they do, ask if you can be notified before they spray. This will allow you to cover your plants ahead of time and hopefully avoid any drift. If this isn’t an option for you, try to place your garden in a protected area that is less likely to be hit with any drifting spray.

To limit herbicide residue exposure at home, there are a few things you can do as well. Create your own compost with known sources like kitchen scraps, cuttings, dead plants, etc. We use vermiculture (worm composting) in our house and it creates the best compost you could imagine. If you don’t have time or space for this, only buy compost through trusted sources. If you use hay or feed for chickens or rabbits, ask sellers if herbicides have been used in their area. Better yet, try to purchase from an organic farmer!

Growing tomato plants is one of the most rewarding parts of a gardening season. They’re simple to grow, but not always easy. Spending time in your garden every day will help you notice problems before they get out of control. If you notice leaf curl, always look at the environmental factors first – water, sun, heat, wind.

Pests are next on the list, followed by disease. Thankfully, most causes of tomato leaf curl are harmless and will resolve with a little TLC. If you do face a fatal reason for leaf curl, chalk it up to experience. As someone who has made every gardening mistake in the book, I promise you are a better, more considerate gardener for it!