Tomato leaves curling is not necessarily an indication of pests or disease but often rather evidence that something is not quite right. And much like yellowing leaves, tomato leaf curl can happen for many different reasons where most, luckily, are quite easily remedied.
We have 50+ tomato plants and cherry tomatoes and Striped Stuffer beefsteak tomatoes account for the majority this year. And based on experience, at least some of my plants will suffer from leaves curling this growing season.
How can I be so certain? Because even if growing conditions are perfect, it may only take one missed watering in the midst of summer for your tomato plants to show signs of stress and leaves to start curling.
9 reasons you suffer from tomato leaf curl (with fixes)
Tomato leaf curl is in itself no reason to panic. But early detection followed by corrective measures is key for your tomato plants to recover.
1. Too much sun and hot temperatures causing leaf curling
Think of the tomato leaves as the solar panels you can put on your roof to harness the energy of the sun.
Much the same way, tomato leaves are there to collect the sunrays to be transformed to much needed plant energy in the process called photosynthesis.
And yes, tomato plants do like full sun. But if your plants get overexposed to direct sunlight or overly hot temperatures the tomato plant will proceed to protect itself.
Tomato leaves curling is the plants way to reduce the surface exposed to direct sunlight and thereby protect against water loss and dehydration as well as sunburn.
Fix: If possible, move the tomato plant to a less exposed location. If tomato plants are planted in the ground, cover each plant with a 30% to 50% shade cloth and observe. The density percentage indicates the percentage of light that is blocked out.
2. Too windy or lack of proper support
When tomato plants get stressed you can experience leaves curling on both new and mature leaves.
Tomato leaves curling curl can also occur when plants are left swaying back and forth due to lack of structure of support. Always make sure each tomato plant is properly staked as needed.
Let me give you an example. When transplanting cherry tomato seedlings I decided to move outdoors. It was a sunny day and it was only early afternoon. It was, however, a bit breezy.
After transplanting 10 or so tomato seedlings I saw twisted leaves as well as leaf roll and curl on some of the transplanted seedlings. I suspected transplant shock.
I quickly made the decision to move indoors and from there on in no more seedlings showed signs of transplant shock, leaf roll or leaves curling.
I learnt that environmental factors like a chilling breeze may cause environmental stress or shock in recently transplanted or potted up seedlings.
Fix: Pay attention to environmental conditions such as location, chilling winds or high temperatures. Provide good support and do not expose tomato plants to windy conditions or even a chilly breeze early in the growing season.
3. Damaged or compacted root systems
Tomato plants need a lot of water to grow and thrive. And even though tomato plants can absorb water through their leaves  it is not a very efficient way for a plant to take up water.
Instead tomato plants rely on most of the water it needs to be absorbed via the root system.
But if the root system is damaged due to for example root rot caused by excessive moisture, the tomato plant will not be able to take up enough water.
Another example can be roots that are damaged or compacted due to for example the use of pots that are too small.
In both of these examples, the plant will not get enough water and you will have a poorly established plant where leaves tend to suffer from both leaf curling and yellowing leaves.
Fix: Use proper sized pots and inspect the root system of your plant every now and then. Also, be observant of leaves turning yellow as it may indicate overwatering that can lead to root damage and even root rot.
4. Leaf curling when you do not water enough
Tomato plants are hungry for water and if you do not water your plant enough the leaves will curl, twist and even go limp and lifeless.
Where we live and garden (zone 7) it can be enough to miss watering one early morning on a hot summer’s day to have a plant suffer from leaves curling. Especially since we grow most of our tomatoes in hanging baskets (cherry tomatoes) and grow bags (beefsteak tomatoes) that need more watering than a plant growing in the ground.
Fix: Follow a watering schedule as tomato plants respond well to regular and thorough watering. Be observant on unusually hot days and be prepared to water twice daily if needed.
5. Pests causing tomato leaves curling
Pests can also be the cause of tomato leaves curling. This is especially true for pests that suck plant juices from the tomato leaves like aphids, thrips, and whiteflies  .
As with all cases of pests and diseases early detection and treatment is key for the plant to recover.
Fix: Isolate any one infested plant and then treat with a Neem oil and water solution using a spray bottle. Avoid treating any one plant just before or when exposed to direct sunlight.
6. Herbicide drift
Herbicide drift is simply put herbicide damage caused by herbicides from nearby locations drifting onto your property and giving your plants an accidental dose of herbicide . This unwelcome treatment leads to herbicide damage with the tell tale sigs of plant shock, leaf curl and often a plant beyond rescue.
When we hear the term herbicide drift, most of us automatically think of huge machines and large fields belonging to massive commercial farms.
But herbicide damage is actually more likely to affect you as a home gardener if you or one of your neighbours have been spraying weed killer on a windy day. Or maybe there have been some landscapers tidying up in your neighbourhood?
Fix: Herbicide drift is one of the causes of tomato leaf curl that is hard to reverse. And, as you don't know the type of herbicide that has reached your plants, I would recommend that you destroy any plant that suffer from herbicide damage as well as any one plant growing nearby. Do not place on your compost, an infected plant should be destroyed.
7. Not feeding your tomato plants
Tomato plants are fierce growers and you need to feed your plants regularly starting a week or so after your first pot up of transplant to a bigger pot.
If you fail to feed your tomato plants you will experience stunted growth, decreased fruit production and quite possibly leaf curl as the plant suffers to grow and develop.
Fix: Use a high nitrogen fertiliser in the beginning and then switch to a more balanced all purpose fertiliser when your plants start to bloom.
8. Giving tomato plants too much nitrogen
Loving your tomato plants can easily lead to giving the plants too much nitrogen with leaf curl as a consequence.
The most common scenario is best described as simply over fertilising the plants with a nitrogen heavy fertiliser.
But there is also another scenario. And this has happened to some of my plants more than once.
I fertilise using a high nitrogen fertiliser but also continuously add fresh grass clippings as mulch around my plants. This double dose of nitrogen may work well for some plants whereas other plants develop leaf curl as a protest.
Regardless of how you get there, giving too much nitrogen can cause your leaves to curl and plants to produce malformed fruits.
Fix: Tomato plants should be fed nitrogen heavy fertilisers when the young plants are developing. Later on, when the plants start to bloom, we switch to a more balanced all-round fertiliser that helps the plant with fruit production. If you suspect tomato leaves curling due to the amount of nitrogen given, you should simply stop fertilising and switch to water only. As the excess fertilisers are flushed from the soil you will be able to resume fertilising when the plants have recovered.
9. Curly top virus
I have read a lot about the leaf curl virus but we have luckily never had any problems with leaf curl viral infections in our gardens.
The leaf curl virus is also known as the curly top virus or the curly top disease of tomato  and is a viral infection that affects all types of tomatoes as well as peppers, beans, spinach and beets. There is to the best if my knowledge no disease resistant varieties of tomato plants that is safe from this scourge.
The disease is spread by the beet leafhopper as it passes through your garden. Your plants will start to show the leaf curl symptoms after 7-14 days by which time the beet leafhopper is long gone.
The good news is that there is no evidence of plant to plant spread of the disease. But on the other hand, affected plants are pretty much lost and do not produce any fruits.
Fix: There is unfortunately no known fix as the beet leafhopper will pass on the disease and then move on before the symptoms show and can be treated. Destroy the entire plant even though there is no evidence of plant to plant spread of the disease.
Bonus! Physiological leaf curl
Physiological leaf roll  or curl is best described as tomato leaves that show all the signs of curling where there is no evidence of disease or viral infection.
And it gets even more confusing as plant growth, fruit yield and fruit quality is reported to not be affected.
Still gardeners look for reasons to why and how to fix.
What we know is that physiological leaf roll is more common in high nitrogen growing environments where there are phosphate deficiencies.
Further, it seems like over pruning can be a trigger and that indeterminate varieties are more susceptible than bushy tomatoes.
Finally, both dry soil conditions and excess soil moisture coupled with high temperatures have been known to trigger the condition.
Fix: Choose determinate tomato verities, maintain a consistent soil moisture and temperature, make sure to balance nutrition given and be mindful of over pruning. But on the other hand, should gardeners care when neither fruit quality or production is affected? I leave that one for you to answer.
Do you destroy plants suffering from curling tomato leaves?
As a rule I would say no. But in some cases we have no choice.
In most cases tomato plants will bounce back if you catch the curling leaves early and can fix the underlying problem.
After all, curling leaves are not a disease but rather an indication that something is not right.
Early detection is key and most plants will recover.
But with severe cases of for example underwatering you may not be able to rescue the plant. This has happened once or twice over the years, but it is rare.
And then there are the times when we do not want to try to rescue the plant. For us this would include tomato leaf curl due to herbicide drift.
Finally, there are the instances of tomato leaf curl where the plant cannot be rescued, like curly top disease of tomato.
And remember never to compost plants that are affected by disease or herbicide drifts.