My Basil Leaves Are Curling – Why Do Basil Leaves Curl Under

My Basil Leaves Are Curling – Why Do Basil Leaves Curl Under

By: Mary H. Dyer, Credentialed Garden Writer

Help! My basil leaves are curling and I don’t know what to do! Why do basil leaves curl under? The reason for basil leaves curling up may be environmental, or your plant may be diseased or pestered by pests. Read on to learn more about this frustrating problem.

Reasons for Basil Leaves Curling Up

Generally, growing basil in the garden is easy and stress-free. That being said, problems can and do arise. Basil leaf curl treatment is dependent on the specific factor causing it. Here are the most common stressors leading to curling basil leaves.

Sunlight – Basil is definitely a sun-loving plant and exposure to less than six hours of bright light per day may result in distorted foliage or basil leaves small and curled. Relocating the plant to a sunnier location may solve the problem.

Water: Too much or too little – Basil requires regular water, but not too much. As a general rule, water the plant deeply whenever the top 1 to 2 inches (2.5-5 cm.) of soil feels dry to the touch, usually once every four to seven days. However, keep in mind that potted plants may require more frequent irrigation, especially during hot, dry weather.

Whether the plant is in the ground or in a container, be sure the soil (or potting mix) is lightweight and drains well. Water at the base of the plant and keep the leaves as dry as possible.

Diseases – Fungal diseases may be the cause of basil leaves curling up, but chances are, you’ll notice other telltale signs. For example, powdery mildew is a fungal disease that causes a grey, powdery substance on the leaves. The disease is caused when conditions become too moist, including too much shade or soggy soil.

Fusarium wilt, which is usually deadly, can cause brown or distorted leaves. To prevent moisture related diseases, water basil carefully as directed above.

Pests – Basil is a hardy plant, but it can sometimes be bothered by aphids and other small, sap-sucking pests such as spider mites or scale. The pests can be difficult to see, but a close look at the leaves, especially the undersides, will usually tell the tale.

If you determine your plant is infested with bugs, insecticidal soap spray usually keeps the pests in check. Be sure to spray when the foliage is in the shade; otherwise, the spray may scorch the plant. Don’t spray when the temperatures are above 90 degrees F. (32 C.).

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Hydroponics & Leaf Curl

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Plants grown hydroponically rely on the liquid-nutrient mixture you provide to sustain them and help them grow. Their roots rest in perlite or another non-soil material that helps guide the nutrients to the roots without providing essential nutrients on their own. The fertilizer balance in your solution is the most likely reason the leaves on your plants are beginning to curl.

Basil problem: leaves are puckered, bubbly

I'm growing basil from seeds. About 100 have grown to small seedling stage. 20 of the plants appear normal, but 80 have strange leaves. The pictures below show the problem.

In these plants, the lamina was already puckered and bubbly at the development of the first true leaves. Some of the leaves are curled in a deformed way, but many have a normal shape. Despite the puckered lamina, the 80% of plants with the odd leaves are growing just as fast as the 20% which are normal. Interestingly, the strange plants are similar to the normal plants in other ways: they're green, feel plump, and have a very normal (and delicious!) basil smell.

I've looked mornings and evenings to find bugs on the undersides of the leaves, but haven't found anything.

Growing conditions: outdoors, in small pots and a seed tray, 10 hours of direct warm summer sun, soil used is just soil from my garden + home compost. There are hundreds of other plants and trees around the basil plants (in my garden and wild), but none of them have the same problem. I've grown basil before in the same conditions and I got normal, smooth leaves on all plants.

I've looked a lot on the internet for possible causes. The grower in this post on houzz five years ago has a basil picture that looks a bit like my situation, but unfortunately there was no resolution and the plant didn't fare well. I've seen diseases like peach leaf curl (taphrina deformans) and cucumber mosaic virus which have some similar effects, but they don't look quite like the leaves of my basil additionally, I couldn't find any examples that they affect basil at all.

So, I have no idea where to even begin to understand and help these basils. Any ideas what is going on?

Spinach leaves curling/cupping under

Well this post could go here, in hydroponics, or even in herbs. But I figured I'd probably get the most attention here so this is where I've come.

I'm currently growing (among other things) spinach and sweet basil in a DWC hydroponics system I built. For those not familiar, this is plants suspended over a large reservoir of nutrient solution that is being vigorously bubbled with an air pump. Roots extend downward into the water so that some get nothing but air, some get air and water, and some get aerated water. Lettuce and most leafy greens grow like crazy in this. (My lettuce grows so fast I can hardly eat it fast enough.)

Anyway, my spinach leaves are growing very "bubbly" looking add they tend to curl downward all the way around so that the leaf is almost half as big seen from above as it would be if it laid flat. I know that spinach doesn't usually grow perfectly smooth leaves, but this amount of curling up seems strange to me.

Also, the sweet basil is doing the same thing except its leaves are very cup-shaped. I could literally pick a leaf and use it upside-down to hold a few ounces of water.

The plants seem to be otherwise very healthy, and taste great.

What causes citrus leaves to curl?

Citrus trees are hardy plants and can grow in adverse conditions. Orange trees, lemon, kumquat, and grapefruit trees among others are quite easy to grow because of their hardiness. Curling leaves on these trees is probably a sign of disease, pests, or other problems affecting the plant.

Here are the possible causes of leaf curl in citrus trees:

Pest infestations

A common reason for leaf curl in citrus trees is insect infestation (pest attacks). Common pests that may be affecting lemon and orange trees include mealy bugs, aphids, mites, and scale.

These pests are known to feed on the leaves by sucking the sap directly from them, causing the leaves to curl and cup downwards. You can identify pest attacks on lemon, orange, lime, and other citrus trees by checking the underside for pests.

If you see small insects on the underside of leaves, they’re probably the cause of the leaf curl symptoms. Simply apply an insecticidal soap to get rid of them. Keep in mind that when they’re many, they can also lead to discoloration and drying of leaves.

Nutrient deficiency

Potassium and iron deficiency in citrus trees such as oranges, for example, can cause symptoms such as leaves curling and turning yellow. This problem usually stems from a soil pH that’s too high.

Correcting soil pH with the right fertilizer and supplementing with iron in orange trees will stop and treat the curling leaves in most citrus trees. A good fertilizer for citrus trees that’s low in phosphorus and high in nitrogen will help correct the pH and nutrient deficiency problem.

I’d recommend a foliar nitrogen-rich fertilizer for citrus trees such as urea to help improve the health of your lemon, orange, meyer and kumquat trees to prevent curling and discoloration.

Extreme cold or heat

Generally, citrus trees such as satsuma and kumquats are great at tolerating extreme temperatures. However, most citrus trees do not do so well in extreme cold or heat, and may exhibit leaf curl as a sign of temperature stress.

  • Too much heat in summer dehydrates the plant, forcing the leaves to curl and lose shape due to lack of adequate water.
  • Freezing temperatures in winter cause the leaves of citrus trees to become brittle and deformed.

You may be able to fix the temperature problems for indoor potted citrus plants by regulating the temperature in your house to a suitable environment that these fruit trees like.

Citrus tree diseases

Fungal diseases can also cause citrus leaves to curl, lose color, wilt, and even drop prematurely. The most common citrus fungal diseases that cause curling leaves are botrytis disease and bacterial blast.

If your plants already have sap-sucking insects such as aphids, mealybugs, and scales, you may also notice a black fungus that appears as a moldy coating growing on the underside of the leaves of your citrus trees.

This fungus likes to grow and feed on the sticky substance that the insects produce, and may contribute to the curling of leaves of citrus trees such as lemons and oranges.

Inadequate water (drought)

When citrus leaves curl inward, it is probably a sign of lack of enough water. You might want to check around the base of the tree whether it is potted or grown in an outside garden to see if the soil is dry.

Drought usually causes leaf curl in citrus trees, only that the leaves do not lose their green color as is common with nutrient deficiencies. The easiest fix for this problem is maintaining a proper watering routine for your citrus trees as explained under treatments below.


In some citrus trees, especially potted orange trees, ovewatering can also cause leaves to start curling and even wilting or drooping. Leaf curl is not the only problem since you may start to notice discoloration (usually yellowing) and falling.

Other symptoms may occur due to root rot in citrus trees, such as stunted growth, dark spots on the stems and leaves, and even dying.

Seedling Problem No. 10

Yellow spots or black mold on first few sets of leaves

Cause: Whiteflies are common pests of indoor gardens that may prey on weak seedlings. They suck sap from plants, leaving behind yellow spots. Worse, when they suck out more plant juice than they can digest, the pests excrete the excess as a sticky substance (called "honeydew") on leaves. The sooty black mold grows in the honeydew.

Solution: The safest way to protect seedlings is with sticky traps that capture the flies before they can do any damage. When the plants get a little larger, you can eliminate whitefly infestations with Safer® Brand Insect Killing Soa p, a spray that's compliant for use in organic gardening.

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