If you’ve ever grown basil, you’ve probably seen your basil leaves curling downwards and wilting or basil leaves curling upwards and folding in on themselves. Sometimes you may even see basil leaves curling and also looking yellowed or otherwise discolored. Often, these symptoms are just your plants’ reactions to environmental stress such as extreme heat, cold, or high winds. But sometimes basil leaves curling indicates a need for significant intervention on your part. Fortunately, once you’re familiar with the telltale signs, you’ll know what your sweet basil is trying to tell you and you can act accordingly to fix the trouble.

Are basil leaves curling a cause for concern?

That depends. How many leaves on the plant have curled and how are they curling? See additional symptoms like dropped or discolored leaves or signs of insect pests wreaking havoc? Although some basil varieties have naturally curly or frilly foliage, leaves curling is generally a sign that plants need help.

What do curling basil leaves look like?

Basil leaves may look leathery and begin to droop or curl downward. Conversely, leaf tips and edges can also roll upward and inward. In extreme cases, leaves fold in on themselves and may even turn brown and crunchy. Leaves can also look wrinkled or twisted.

8 Possible reasons for basil leaves curling

Some possible reasons for basil leaves curling include underwatering, overwatering, temperature extremes, problems with soil pH levels, nutrient deficiencies, and even faulty pruning. Attacks from the usual suspects like whiteflies, aphids, and spider mites or diseases such as downy mildew and fusarium wilt may also be to blame. The following sections address each of these issues in turn.

1. Insufficient water can cause leaf curl

Underwatering is one common reason basil leaves curl downward. If your plants lose too much moisture, individual leaf cells can no longer maintain their usual shape. This can lead to the entire plant drooping and wilting. Without adequate water, plant leaves eventually will drop off and the plant will die. Here’s how to properly water basil plants.

2. Overwatering can lead to basil leaves curling

Excess water can cause leaves to droop and turn yellow. Deluge basil plants too often with too much water and you’re putting out the welcome mat for root rot and other fungal diseases. That’s especially true for potted plants in soil that drains poorly. The fix? Remove the affected plant, trim away any decaying roots, and repot with fresh potting mix in a pot with drainage holes. This is also an opportunity to replant in a larger pot if need be.

3. Pests and diseases that cause basil leaves to curl

Certain insects or fungal diseases may be the culprits behind your basil leaves curling up. Affected leaves may look leathery, wrinkled, or twisted. Additionally, if you look closely, you may see signs of white fly, slugs, spider mite, aphid, or other pest activity. In particular, check the underside of the leaves for the critters themselves and examine the whole plant for sticky residue, webbing, stippling, or discoloration.

While examining the undersides of curled leaves, you should also be watching for gray-, white-, or sooty-looking spots which can be caused by diseases like botrytis, powdery mildew, downy mildew, and fusarium wilt.

4. Temperature fluctuations can result in basil leaves curling

Exposure to too much direct sunlight, wind, or high heat can cause significant water loss for your plants. To reduce the amount of surface area being exposed to the elements, plant leaf edges roll up and inward. If you catch this before the whole plant’s affected, you may be able to salvage it. Shading basil plants during the hottest parts of the day can help remedy the situation during heat waves.

5. Lack of nutrients

Leaf curl and discoloration may indicate certain nutrients are lacking or your soil pH is out of whack. For instance, on older leaves toward the base of the plant, if their veins look green but the surrounding areas are turning yellow and curling, that’s likely a nitrogen deficiency. But, if you see similar symptoms affecting younger curling leaves, that’s typically a lack of manganese.

Fertilization mistakes like “burning” plants by applying too much fertilizer—especially synthetics with very high N-P-K ratios—can also cause basil plants to curl.

6. Improper pruning can lead to basil leaves curling

You should allow basil plants to reach at least six inches in height before you prune them. If you remove a basil stem or multiple stems too soon or cut too much of them away at one time, it is possible to stress your plants enough to cause leaf curl.

7. Some basil varieties curl more than others

The growth patterns of certain basil varieties have naturally cupped leaves. Some of these include Genovese basil, Monteverde late flowering basil, and disease-resistant cultivars like Prospera Compact DMR. Others like lemon basil and lime basil have flatter-looking leaves. Keep natural growth habits in mind as you monitor plants for trouble.

8. Old and “tired” plant

Basil leaves curling may simply be a function of your plant’s age. If you allow it to bud, flower, and set seed, you’ll no longer be able to harvest abundant and exceptionally flavorful leaves. Your basil’s “job”—to reproduce by setting seed—is finished. As such, the leaves on these subsequently woody shrubs may curl up and die back, rather than continue to put out healthy new growth.

Solutions for basil leaves curling

• Adjust watering frequency and amounts—If the top inch of soil looks and feels very dry, add water. Allow your basil plants to dry a bit between watering sessions and avoid overwatering.
• Apply insecticidal soap—If you can’t manage an insect infestation through hand-picking and removal alone, you can use an all-natural insecticide. Just don’t apply during the hottest, sunniest part of the day, as this can burn your plants. Also, note that these will affect beneficial bugs, too!
• Manage environmental stressors—Establish wind breaks and use shade cloth to give plants a rest. In low humidity, mist leaves or, indoors, use a humidifier.
• Improve soil conditions—Basil will grow best in a (slightly acidic) pH around 6.0. Gauge pH and fertility with a soil test kit. Amend with organic matter as needed. Add mulch to insulate roots and conserve moisture.

How to prevent basil leaves curling

By putting the ideal conditions for your plants in place and offering consistency of care, you’ll promote healthy growth and keep trouble at bay. Basil plants thrive in stable environments with temperatures between 80 and 85 degrees F or higher (27 to 30 degrees C). Basil needs adequate drainage and about an inch of water each week. Enough light—at least six hours of bright light daily—is also critical.

Straightened up

Whether you grow your plants in pots on window sills, in a greenhouse, or in an outdoor vegetable or herb garden, there are many reasons why you might notice your basil leaves curling. Remember, some of the most common causes of leaf curling include watering mistakes, insect or disease issues, poor pruning, or environmental stressors such as a low humidity level, excessive wind, or too much heat and sun.

With vigilance and proper longterm care, you can often prevent these problems. The sooner you notice basil leaves beginning to curl and exactly how they’re curling, the sooner you can address the issue, and, usually, there is a fairly easy fix.

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