Curling tomato leaves is a common problem that growers face in the garden. Its root cause can stem from a variety of sources, so this article will cover some of the most likely culprits behind tomato leaf curl.
I want to start by saying it is rare to have a tomato without any curled leaves. In many cases, curling tomato leaves is a natural symptom of environmental conditions. In other words, it’s nothing to worry about!
However, there are some instances where you may want to intervene and help your plants recover. So, let’s get into why your tomato leaves are curling.
1. Overwatering (Or Poor Drainage)
One of the first things to check is your watering habits. Tomatoes require plenty of water on a regular basis. However, too much water in the soil can lead to curling leaves.
If you are growing in containers, make sure your pots have drainage holes. Without drainage, the soil will become waterlogged, drowning the root systems of oxygen.
For in-ground plants, perform a drainage test to see how well your soil drains. If your soil contains more clay, it may need some added compost or sand to help it drain more freely.
Other symptoms:
- Drooping leaves
- Soggy soil
Solutions:
- Improve drainage
- Water less frequently
2. Environmental Stress (Physiological Leaf Curl)
Some of the most common causes of tomato leaves curling up like a taco shell are based on the environment. High temperatures, strong winds, and low humidity can all combine to cause tomato leaves to curl.
While tomatoes can certainly handle high heat, they may show some signs of stress when it gets really hot. If your summer weather is above 90°F, your tomato leaves may curl as a defense mechanism.
Similarly, if your plants are grown in a location with strong winds or lower humidity levels, tomato leaves may curl in response. These conditions are difficult to control, but also rarely cause major crop loss.
Symptoms:
- Older leaves curling
- Curled leaves are full formed (no spots, no browning, holes, etc.)
Solutions:
- If the plants are still productive, it is often not necessary to intervene
- For high heat, shade cloth can be used to reduce ambient temperatures
3. Herbicide Damage
Herbicides have no business being in your vegetable garden. However, there are a number of sneaky ways that they can end up affecting your tomato plants.
Compost and manures can often be laced with herbicides. This is caused by cows and horses eating hay that was originally sprayed with herbicides in the field. The herbicides do not break down, and wind up in bagged manures.
If your lawn gets fertilized, some fertilizers have added herbicides to kill lawn weeds. These are sometimes labeled “weed and feed” fertilizers. If you mulch with your grass clippings or use them in compost, they can end up in the garden.
Lastly, if you happen to live nearby a farm of any kind, it is very possible that they spray with herbicides. These sprays can drift on the wind (up to a mile or two) and end up blanketing the surrounding areas with herbicide drift. Call any local farms to learn more about their spraying program.
Symptoms:
- Twisted, deformed leaves
- Smaller leaves
- Shriveled leaves
- Dying leaves or plants
Solutions:
- Avoid bagged horse manures
- Make your own homemade compost
- Do not compost or mulch with lawn clippings if you use “weed and feed” fertilizer
4. Disease
If you’ve grown tomatoes, then you have probably seen some form of tomato disease. There are many types of viruses and fungal diseases that impact tomatoes, many of which cause the leaves to curl.
In addition to leaf roll, most diseases will cause other symptoms. This can help diagnose the disease in question, and what action you may want to take.
In most cases, diseased foliage should be removed from the plant as soon as it is seen. Other diseases require you to remove the plant from the garden to prevent further infection or contaminating your soil.
Symptoms:
- Spots or holes on leaves
- Yellowing or browning
- Fuzzy growth
- Rotting fruits
Solutions:
- Identify the disease in question
- Remove diseased foliage from the plant
- Keep cleanly by sanitizing gardening equipment
- Keep pests under control by growing companion plants
- Avoid smoking in the garden or touching plants after smoking
5. Pest Damage
A variety of pests can feed on your tomatoes, causing curled leaves. One that stands out as a potential culprit are broad mites. These tiny bugs come and go from the garden, and can feed on a variety of plants, including tomatoes, peppers, and eggplants.
Broad mites prefer shady locations, and tend to feed on younger foliage. So, the curling leaves will often first appear on the newer leaves forming on your tomato plants.
Broad mites are very small, between 0.1-0.3mm, and their eggs are even smaller. They can be brought into your garden on transplants from the nursery, or by hitching a ride on other, larger pests.
Symptoms:
- Younger leaves curled first
- Tiny oval shapes bugs on leaves
- Tiny eggs on leaves that almost look like they sparkle (silvery and spotted)
Solutions:
- Spray plants with miticides
- Try predatory mites
- Remove severely infested plants from the garden
Other Causes of Tomato Leaf Curl
There are more possible causes for your tomato leaves curling, many of which can easily be fixed. Here are a few more possibilities:
- Leaf scorch. It is common in early spring for young tomato plants to be burned by direct sunlight. The leaves will turn off-white or gray, and become crispy to the touch. To prevent this, harden off your tomato seedlings gradually.
- Excessive pruning. If you prune your tomato plants too often, it is possible that they will become stressed. Try to prune at regular intervals, about once every 1-2 weeks for indeterminate types.
- Over-fertilizing. If you feed your tomatoes too much fertilizer, they can become stressed. This can cause yellowing or browning leaves, and possibly curling as well. Always follow recommended guidelines on fertilizer packaging, and err on the side of less rather than more.
Watch more about tomato leaf curl (video):
I hope this article helps you understand why your tomato leaves are curling. In most cases, curling leaves is nothing to worry about. As long as your plants are otherwise healthy, a few curled leaves is not a problem.