Why Are My Tomato Leaves Curling? – Causes, Prevention and Treatment

While tomatoes are some of the best tasting items to come out of the garden, these plants are susceptible to their fair share of issues. One common symptom of a larger issue is curling leaves.

If you’ve noticed your tomato leaves are curling, you’re not alone! I’ve seen my fair share of curled tomato leaves over the years, with various environmental conditions, diseases, and nutrient deficiencies to blame.

The truth is that there are many possible causes of curling tomato leaves, and it can be difficult to determine what is affecting your plant. That said, it is possible to diagnose what’s causing your tomato leaves to curl!

Join me as I introduce you to seven common reasons your tomato leaves may be curling, as well as ways to prevent and solve each issue.

What to Look for In Curling Tomato Leaves?

Before you determine the cause of why your tomato leaves are curling, it can be helpful to get a good picture of what’s going on with your plant.

Take a good look at your plant and describe what’s occurring as accurately as possible. You’ll use these details later to help you better diagnose the cause of the curl.

If you don’t know where to start, ask yourself the following questions.

  • Are the tomato leaves curling upwards or are they curling downwards? Is the curling occurring on new leaves, old leaves, or both?
  • You should also look for other co-occurring issues. For example, are the leaves turning yellow or black, or are they a healthy green?
  • You should also take note of the overall health of your tomato plant. Does it seem to be growing well and thriving, or is its growth stunted?

By carefully observing your tomato plant, you will be better able to determine why the leaves are curling.

7 Reasons Why Your Tomato Leaves Curling

If you’re wondering why your tomato leaves are curling, check out these seven common reasons.

1. Lack of Water and Hot Temperatures

If your tomato plant is exposed to hot temperatures and can’t get enough water, it may respond by rolling its leaves inward. This is known as physiological leaf roll.

This type of curling begins with older leaves. Leaf edges curl inwards and eventually, the tops of the leaves may roll towards each other.

Some varieties of tomatoes are more susceptible to physiological leaf than others. In general, indeterminate varieties are more likely to be impacted than determinate varieties.

While it can be alarming to see leaves dramatically curling, it’s important to realize that this type of leaf curl is not harmful. It generally does not impact plant health or fruit yield.

Prevention and Treatment

While this type of leaf curl will not harm plants, you can still do your best to prevent it.

Ensure that you never let the soil dry out by watering regularly. You should also avoid pruning your plants during hot conditions, since this may encourage leaf curl.

If you notice your leaves are curling due to heat, there’s not much you can (or need to) do. Trust me, the plants will be just fine once the weather settles.

I’ve witnessed rows of tomato plants curl their leaves one day only to appear normal the next.

2. Planting When it Is Too Cold

If you transplant tomato plants outdoors when it’s too cold, they may respond by curling their leaves. This is especially true if you fail to properly acclimate them to outdoor conditions.

If transplant shock and/or cold temperatures are to blame, leaf curl will begin with lower leaves rolling inwards. The leaves may remain green as they curl, or they may turn yellow due to stress.

Prevention and Treatment

The best way to prevent this type of curling is by stressing your tomato plants as little as possible.

Begin by properly acclimating your transplants to the outdoors, a process known as hardening off. You can begin hardening off your tomato seedlings when nighttime temperatures remain above 60ºF.

I like to move my potted tomato seedlings outdoors for a few hours one day and then a few more hours the next. I continue this process until the seedlings spend a full day outdoors.

At this point, the tomato seedlings can be transplanted into the ground.

If you notice the plant’s leaves are curling after transplanting, patience is the best practice. As long as temperatures are warm enough and you’ve properly hardened off your plants, the tomatoes will bounce back within a week.

3. Calcium Deficiency

Calcium is a plant secondary nutrient, which means plants need a relatively large amount of calcium to thrive. This holds true for tomato plants.

If tomato plants are not able to take up the calcium they need, their leaves may begin curling inward. Leaf curl will start with younger leaves.

Additional signs of calcium deficiency in tomato plants include newer leaves turning yellow while the veins remain green. As plants develop fruit, the tomatoes may also exhibit rotten tips, a phenomenon known as blossom end rot.

Prevention and Treatment

The best way to prevent calcium deficiency is to ensure your tomato plant has access to—and can absorb—the calcium it needs.

The best way to determine whether or not you need to apply calcium is to conduct a soil test. A proper soil test will tell you how much calcium is in the soil, as well as other important factors like soil pH.

I recommend taking a soil sample and then submitting it to a professional soil testing lab. You can check with your local county or state extension service to see if they offer soil analysis services.

If test results show that both calcium levels and soil pH are low (pH below 5.5), you can add lime to correct both of these issues. If the pH is at an appropriate level (between 5.5 and 6.5), you can add gypsum to add calcium.

While many people assume symptoms of calcium deficiency in a plant indicate a lack of soil calcium, this isn’t always the case. Even if there is enough calcium in the soil, plants will have a difficult time taking it up if there is not adequate soil moisture.

Dry soil, or inconsistent watering, can also lead to calcium deficiencies in tomato plants. Aim to keep the soil consistently moist, and water when the two inches of soil are dry. Do not overwater your tomato plants.

If you notice signs of calcium deficiency in your tomato plants, make sure you are watering your tomato plants regularly. If the soil moisture is at an adequate level, you can attempt to remedy the issue by foliar feeding with liquid calcium.

4. Copper Deficiency

A lack of copper in your plant can also cause the leaves to curl. In this case, the leaves will curl upwards.

Other signs of a copper deficiency include bluish-green leaves and an overall lack of growth. Over time, lower leaves may become yellow and fall off the plant.

Prevention and Treatment

The best way to prevent a copper deficiency is to ensure your tomato plants have access to an adequate amount of copper. Copper is a micronutrient, which means plants don’t need a lot of it. However, a deficiency can lead to serious issues!

Before you plant your tomato plant, test the soil to check and see if your soil has an adequate amount of copper. If it does not, you can apply copper sulfate to the soil following the soil test results.

If you notice your plants are showing signs of a copper deficiency, it may be too late to reverse the damage. However, you can try applying copper via foliar feed.

Biomin copper is a chelated form of copper that is immediately available for plant uptake. Be aware that you will only need to apply a very small amount of this copper to each plant—about 1/10 of a teaspoon.

5. Tomato Yellow Leaf Curl Virus

Certain plant diseases can also lead tomato plant leaves to curl. One of these diseases is tomato yellow leaf curl virus.

The signs of this virus first appear in newer leaves. These leaves’ edges curl up or down and also turn yellow. Over time, leaves may also be smaller in size, and plants may drop their flowers and/or fruit.

The virus is spread by a small sap-sucking insect known as the silverleaf whitefly. This pest has a small yellow-orange body covered with two white wings.

Prevention and Treatment

Do your best to avoid bringing this disease into your garden. This means you should buy transplants from reputable sources and carefully inspect seedlings before bringing them home.

If you notice a plant develops the virus, you should remove it from your garden. This will help the virus spread to other plants.

When you remove the plant, place it in a plastic bag in the trash rather than in the compost.

You can also help prevent the spread of the virus by controlling the whiteflies which serve as a disease vector. If you notice whiteflies on your plants, you can spray them with neem oil or insecticidal soap.

Although this virus is primarily a concern on tomato plants, it feeds on hundreds of different plants. Therefore, you should also monitor other plants for these pests and spray as necessary.

As far as treatment goes, there isn’t a good option. Your best bet is to remove the plant to prevent others from becoming infected.

6. Tomato or Tobacco Mosaic Virus

Two other diseases that can cause curling leaves are tomato mosaic virus and tobacco mosaic virus. Although these are two different viruses, they present similar symptoms.

Both viruses can lead to tomato leaves with edges that curl inward or outward. The plant’s leaves may also develop yellow or brown patches.

Additional symptoms include distorted or stunted plants as well as small or oddly shaped fruits.

These viruses can be spread in numerous ways, and you must understand the various ways they can infect your crops.

First, this virus can be present in infected seeds. If this is the case, the resulting plants will likely be infected.

The virus can also be introduced by touching the plants with infected tools or hands. Additionally, tobacco mosaic virus can be introduced if an individual uses tobacco products near the plants.

Insects like aphids and leafhoppers can also spread the mosaic virus between plants.

Once these viruses are in the soil or plant matter, they can persist for many years. Therefore, it’s imperative to avoid introducing these diseases into your garden.

Prevention and Treatment

As mentioned above, you should avoid introducing these viruses into your garden at all costs.
Once they are in the soil, they are extremely difficult to get rid of.

Start by only buying seeds and transplants from trusted sources. All reputable seed companies will test their seeds for these viruses. Some companies I like include Johnny’s Selected Seeds, High Mowing Organic Seeds, Osborne Quality Seeds, Adaptive Seeds, and Seed Savers Exchange.

To prevent the spread of diseases between plants, sanitize pruning tools regularly. You should also avoid using tobacco products around your tomato plants.

If you do notice signs of a mosaic virus on a tomato plant, you should dispose of it to prevent it from spreading to other plants. Remove the entire plant and place it in the trash—do not compost it.

7. Exposure to Herbicides

Herbicides designed to kill broadleaf weeds can also damage tomato plants.

One of the most apparent signs of herbicide exposure is leaves that curl inward and also appear twisted and contorted. Tomato stems may also curl and twist.

Some of the most common herbicides that impact tomato plants are glyphosate, atrazine, and clopyralid.

Even if you didn’t apply herbicides anywhere near your garden, chemicals still may be responsible for the curling leaves. That’s because herbicides can enter gardens in numerous ways.

If you live in a rural area, herbicides can drift in from surrounding fields. Since broadleaf herbicides are used to kill weeds in corn, herbicide drift may be to blame if you live near conventional corn fields.

Herbicides can also enter your garden through the application of mulch and/or compost. Farmers often apply broadleaf herbicides to grass crops like wheat, rye, and oats that are later used for straw.

If you applied sprayed straw as a mulch in your garden, the herbicides may leach into the ground. This can then affect tomatoes and other plants.

Herbicides can also enter the soil through compost. This is especially true if you apply compost that is made from animal bedding, since straw and hay may have been sprayed with herbicides.

While many herbicides break down in the soil within a few weeks or months, others can remain for months or even years. These are known as persistent herbicides and are the products that are most likely to occur in compost.

Prevention and Treatment

It may sound obvious, but the best way to prevent this issue is by avoiding herbicide exposure. First, make sure to avoid applying herbicide near your tomato plants.

You should also investigate where you are sourcing any compost, straw, and/or hay you use. If you are not sure if straw or hay was sprayed with herbicides, it’s best to avoid using it.

Once you notice tomato leaves are curling from herbicide exposure, there is not much you can do to save your plants. Removing any sprayed hay/straw mulch may help, but the plants may still not survive.

Prevent Is Best, Quick Action Is Next

Now that you know the various reasons why tomato leaves may curl, you can do your best to prevent the issues. Remember, prevention is always better than treatment!

If you do notice your tomato leaves are curling, aim to diagnose and treat the cause ASAP.

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