You may not know exactly what is causing this, but one thing is for sure - it doesn’t look healthy, and it certainly indicates a more serious underlying problem.

The foliage of our plants tells us a lot about them - it’s where we can look to identify nutrient or pH problems, for example. It’s also the place where you’ll identify common pests and diseases, as bugs love to feast on these.

When our plants are suffering from environmental stress, either by heat or changes to their atmosphere, the leaves may start changing as well. With so many different plant problems being related to the leaves, it can make diagnosing the root cause of the issue difficult.

Worry not, because in the coming minutes, we’ll teach you everything that could be causing your plant’s leaves to start curling up. Then, we’ll explain how to remedy each potential cause.

What Tomato Leaf Curl Up Could Indicate

We already know that a lot of issues in the grow room or garden will produce similar symptoms in our plants.

This makes keeping our plants healthy tough. But we’ll explain how to remedy the issue later on. First, we need to explain the reasons this might be happening in the first place.

Rule Out Excessive Heat & Light

The most likely cause of tomato leaf curl up is usually excessive heat and or light energy.

excessive heat and light can cause leaves to curl up

There are two specific instances in which this is a common occurrence:

Outdoor growing during the summer in hotter climates
Indoor growing when young plants are exposed to intense grow lights for the first time.

But, heat and light stress in plants can present itself anytime where you hang your grow lights too close to your canopy, or temperatures exceed the ideal range for plant health.

If you’re growing indoors, particularly with MH/HPS grow lights, you’ll need to constantly monitor the temperature. Keep the growing space between 70-80 degrees Fahrenheit. When you correct the temperature, your plants will bounce back quickly.

To determine if it’s heat from your grow lights affecting your plants, examine the plants closest to the grow light - if the ones directly centered under the light are more curled, it could be heat/light stress.

We have an entire guide on managing heat in the growing space, and we’ll cover it more in-depth later on. Let’s move on to another potential cause of tomato plant leaves curling up.

Root Problems Related To Overwatering

One of the most common growing mistakes for novice gardeners who are growing tomatoes is overwatering their plants. Excess water can quickly contribute to the dreaded tomato leaf roll.

This can lead to root rot, early blight, fusarium wilt, slow plant growth, among many other problems. One of the symptoms of overwatering is tomato leaves curling up on your plants.

You can differentiate between overwatering and heat stress by looking at the plant in general. If it’s showing signs of wilt and looks overall droopy, it could be root problems from overwatering.

Extreme Humidity Can Cause Tomato Leaf Curl Too

A third and final potential cause of leaves curling up is extreme humidity in the grow space. Many growers struggle with grow tent humidity in particular.

Extreme Humidity Can Cause Foliage Curls Too

If you’re trying to cram a lot of plants in a small space, this is an inevitable problem.

You can easily determine if this is what’s plaguing your grow by keeping a hygrometer in the growing space.

You should keep humidity in the ideal growing range of between 50-70% during veg and 40-50% during flower.

If you ignore this problem, it can lead to a myriad of fungal issues. Bud rot, powdery mildew, septoria leaf spot, and other fungal diseases are all likely, and can quickly ruin your crop and force you to scrap your plants and start anew.

Check For Sucking Pests On Your Leaves

When you're dealing with tomato plant leaves curling up, it generally means they are shocked or dehydrated. If you don’t believe the issue to be related to your environment - heat or humidity - it could be related to pests.

In particular, pests that suck the juices from your foliage will contribute to your plant leaves curling up. A few that come to mind are aphids, thrips, and whiteflies.

While these are more common when growing outdoors, it’s easier than you think to develop an infestation indoors too.

By growing in a tent and keeping your environment sealed, you can more or less prevent this.

Even still, there are ways you can unknowingly bring bugs into your grow such as infected plants or your pets.

This is why constantly checking the underside of your leaves is important, so you can identify pests before they become a full-blown infestation.

Nutrient & pH Related Problems

The first four potential causes we’ve mentioned thus far are relatively easy to rule out or remedy.

However, a fifth and final potential reason the leaves on your plant are curling upwards could be related to nutrients & pH.

There are a few different deficiencies that cause leaves to curl either downward or upward. A few that come to mind are phosphorus deficiency & nitrogen deficiency.

It’s not as simple as trying to correct the problem by feeding your nutrients at a heavier application rate.

It could be pH that is locking one of these nutrients out, and thus you need to adjust it to the ideal range (between 6-7 normally).

There are also synergistic or antagonistic relationships between nutrients, and there are ideal nutrient ratios you need to be aware of.

By simply following your feeding chart and adjusting your pH before feeding, you can rule out this issue.

Our complete guide to nutrients & pH is a must-read for every grower, new or experienced.

How To Remedy Tomato Plant Leaves Curling Up

One of the things that separate master growers from novice gardeners is the ability to differentiate plant problems that produce the same symptoms.

For example, we already mentioned that tomato plant leaves curling up could indicate excess heat in the grow room, but could also indicate issues with watering, humidity, or even a pest infestation.

It’d be easy to just go one by one trying to address each potential issue, waiting for things to change.

But if you guess wrong, you run the risk of wasting a few days while your plant’s condition worsens. So, you need to look at your grow with a wider lens. Ask yourself the following questions:

Are all the leaves curling up, or just a few?
Are all the plants in your garden/grow room affected, or just 1-2?
What changes have you made to your grow in the days leading up to you noticing this issue?
What can you rule out as a potential problem?

By asking these questions and narrowing down the potential culprit for your tomato leaf curl, you can come up with a more specific plan of attack to remedy the plant leaves curling up.

Here are some tactics to fix each of the potential causes we mentioned above.

Dialing In Your Growing Environment

You can prevent or remedy many of the potential causes for foliage-related problems by getting your grow room environment dialed in.

If you’re growing outside, there is little you can do here other than hope mother nature has your garden’s best interest in mind.

But indoor grow rooms need to be optimized to the proper ranges for temperature and humidity. There are some supplies and equipment you may need to get this done:

Ventilation System - A necessity in any grow room. An exhaust system (fan, carbon filter, and ducting) is essentially a non-negotiable requirement for indoor growing. Even better, include an intake system (with a bug screen to keep pests out) to bring in fresh, CO2 filled air for your plants.
Oscillating or Clip-On Fans - Another must have for the grow room, to increase air circulation and keep temperature and humidity down. These will prevent stagnant air and make your plants dance, building stronger stems and branches in the process.
Dehumidifier - In larger grow rooms struggling with excess humidity, dehumidifiers are necessary to prevent powdery mildew and other fungal problems. Our review of the best dehumidifiers for growing has a unit for every type of grow out there, from hobbyists to commercial facilities.
Air Conditioning - If you live in warmer climates, growing indoors year round will be tough. You’ll need to add in an air conditioner, especially in large grow rooms, to keep the climate in the ideal range.

We have some complete guides to grow room environment in general, as well as how to set up your ventilation system. These two resources alone are all you really need to get temperature and humidity under control.

Learn How To Water Your Plants Properly

If you suspect the issue with your leaves curling up is related to overwatering, it’s as simple as reading our guide on how to properly water plants and start watering less frequently, less heavily, or a combination of both.

You shouldn’t be watering just because it’s been a couple of days, or because the very top of your soil looks dry.

Especially in cooler climates, the bottom of your container could still be waterlogged.

The best way to tell is by either using a soil tester to determine how moist the media is, or by simply sticking your finger into the media.

If it’s try up to your first knuckle (about an inch), you can proceed with another watering.

Of course, using the right garden pots is essential too. If you’re not using fabric pots, you need to make sure your containers have drainage holes in the bottom. Put a saucer underneath, collect the runoff, and dispose of it properly.

Combat Pest Infestations Quickly

If your plant’s leaves are curling upwards due to a pest infestation, you need to quickly eradicate the bugs in question. If you have an IPM strategy in place, this will be way easier.

Early action is key. Start by removing sick or infested plants from the growing space, so you can at the very least salvage those that aren’t being harmed yet.

Then, use whichever pesticide or neem oil product you think is best for the job to spray these bugs and restore balance to your garden.

If you aren’t sure where to start, our review of the common grow room pests will help you narrow down the bug you’re up against.

Then, you can read the complete guide on that bug for products and tactics we recommend in your fight. When in doubt, email or call us and we’ll provide our expertise!

Correcting Plant Nutrition & pH Issues

If you suspect the reasons your tomato leaves are curling up is related to nutrition and pH problems, it’s actually a relatively easy problem to fix - if you act quick.

Most of the time you can unlock whichever nutrients are locked up in your media and get yourself a “blank slate” for feeding by giving your plants a good flush.

We have a complete guide on how to flush your plants to help you do this right. It can really be as simple as completely flooding your media with pure, pH-balanced water for a few feedings.

This will rinse out residual nutrients and salts in the media. It will also force your plant to use whichever nutrients are stuck within its cell walls. For even better results, use a flushing agent. These are specially chelated to flush more effectively and efficiently.

The result is usually a slightly stressed plant, followed by explosive plant growth (caused by the stress).

You can use an EC meter to determine whether you need to do additional waterings, or you can return to your regularly scheduled nutrient regimen.

Final Thoughts On Tomato Leaves Curling Up

We’ve covered the most common reasons for tomato leaves curling up. And, we’ve shared some tips and tricks on how you can remedy the problem.

In most cases, this is a matter of too much environmental stress, mistakes by the grower in terms of excess water or nutrients, or a pest/fungal disease outbreak.

Now, it’s just a matter of you investigating your own grow. Be diligent, and come up with a detailed plan of attack to rectify the issue in your garden or grow room.

Grab all the garden and grow room supplies you need at Hydrobuilder, and get the best products for less! Our world-class service has growers around the globe coming back for more, time and time again.

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Tomato Leaf Curl: Why Are My Plant Leaves Curling Up?