9 Reasons for Curling Basil Leaves + How to Fix Each

Basil is renowned for its gentle foliage, however, this very same foliage can present challenges for the plant. If you notice your basil plant’s leaves curling, there is no reason to be concerned. By promptly identifying the issue and taking swift action, your basil plant will continue to flourish and yield robust, straight leaves.

Why do basil leaves curl? 

Basil leaves naturally have a light inward curl on the outer edges. However, incorrect watering, poor lighting, and temperature fluctuations can all cause curled leaves. More controllable factors like soil nutrients, growing space, and pH imbalances can also cause abnormal leaf growth.

Basil grows vigorously once established, and while curling leaves may be evident now, with some easy care and mitigation, you can get the problem under control quickly. Read on for 9 explanations of why your basil plant has curling leaves and what to do about it. 

Curling Leaves on Basil Plant – 9 Explanations

A healthy basil leaf will be lightly curled on the underside of the leaf, but environmental factors will also affect your basil plant’s leaf shape. Its leaves will show signs of stress first, so always keep an eye on the plant’s overall growth. 

1. Large Basil Leaves Have a Natural Curved Shaped

As basil grows and matures, its leaves will begin to form a gentle curve at the outer margins that resemble a drooping appearance. This is completely normal and nothing to worry about! 

Solution:

Since this is normal growth, you don’t need to do anything, but spraying a light organic insecticide and inspecting the plant regularly is a great preemptive way to ensure no pests or diseases get the better of your plant. 

2. Overwatering or Underwatering

Basil can be picky when it comes to the amount of moisture it receives. It will attempt to conserve its water by showing signs of stress, like curling at its edges, in drought or over-saturation of the soil. 

Solution:

Monitor the soil moisture to determine if it is in need of more or less water. Basil plants usually require watering about once a week with 1 to 2 inches of saturation necessary for adequate growth. 

3. Poor Lighting Conditions

Lack of adequate sunlight will cause stress on the plant. Over-exposure to high-intensity sun will cause the leaves to pucker and curl upward, and low-light conditions will lead to a wilted or leggy-looking plant.

Solution:

Basil prefers 6 to 8 hours of sunlight, and more or less than this will lead to stressed, curling leaves. Place your basil in a shadier location that still receives adequate sunlight but minimal high-intensity sun. 

4. Fluctuating Temperatures

Another stressor on this tender herb is fluctuating high and low temperatures. Basil prefers spring and summer weather that does not fluctuate outside the temperatures of 50℉ and 90℉. 

Solution:

If you are able to foresee extremes in the temperatures, relocate your plant, use burlap to keep it from cooler temperatures or install shade cloth to reduce sun exposure. 

5. Pests or Diseases

Always keep a lookout for pests. They will usually be hiding on the underside of the leaf’s surface. Aphids and white flies are likely culprits for colonizing leaves’ edges, causing them to curl in stress. 

Diseases like powdery and downy mildew or botrytis mold will form fungal colonies on the leaves and cause the leaves to become distorted and curled. 

Solution:

Inspect both sides of the leaves of your basil plant regularly. If you notice small bugs lining the curled edges of the leaf, spray an organic pesticide like neem oil (this organic neem is fantastic!) or insecticidal soap. Coat the affected area as well as the newest growth to prevent any pests from spreading to other areas of your plant. 

6. Nutrient Deficiency

Basil needs high levels of nitrogen, and without it, the leaves will struggle to grow or might show signs of curling stress. It could also be a minor nutrient deficiency that will result in curled leaves. 

Solution:

If you are able to identify the nutrient your basil plant needs, fertilize it with that specific fertilizer. If not, a general all-purpose vegetable fertilizer (Espoma Organic Garden-tone does wonders!) should add everything your plant needs to thrive! 

7. Poor Soil

Basil can be picky when it comes to soil. Overall poor soil conditions can be related to a lack of nutrients in the soil, poor soil composition, and poor soil density. 

Solution:

Basil loves to grow in loamy well-draining soil that will retain some moisture. Adding organic compost or other soil amendments will help to build the soil while mulch can help to reduce water loss. 

8. Soil pH Too High or Too Low

Soil pH is vital to overall soil chemistry, and out of the acceptable growing range of 6 to 7.5, your basil plant will begin to show signs of irregular growth, like curling leaves and stunted growth. 

Solution:

Test the soil pH to determine if it is in the acceptable growing range. Soil pH relates directly to the soil’s temperature and nutrient balance. If these are incorrect, the plant will suffer. 

9. Improper Pot Size

A basil plant’s leaves will only grow as much as its root system can. If you are growing basil in a pot, it may run out of soil space and become rootbound. 

Solution:

Repot your basil plant to give it more space to grow, or plant it into the ground if possible. Applying fertilizer or compost to the potted plant may help it to survive for a short time, but it will need to be repotted eventually. 

Basil Growing Tips

Caring for your basil plant can be difficult, but here are some other simple tips for growing basil to keep your plant growing for as long as possible!

  • Prune off flowers to encourage more leafy growth and to prevent the plant from ending its lifecycle. 
  • Try not to harvest more than 30% of the leaves. This will allow it to still have enough foliage to grow while not stressing the plant.
  • Prune off any basil leaves you are harvesting right above where the stem splits into two new branches — this helps to make the plant bushier and grow more usable leaves. 
  • Pruning far down the stem may cause the plant to become stressed, so always try to harvest its outer growth. 

Related Questions:

Why Are My Basil Leaves So Small?

Basil leaves will grow to various sizes depending on your variety. Most Italian basil will grow leaves 2 to 4 inches in length while large-leaf basil may grow leaves up to 6 inches in length. If your basil plant has leaves that appear smaller than average, it most likely has a nutrient deficiency. 

Why Are My Basil Leaves Pointed?

Pointed and serrated basil leaves are signs of stress on the plant. While the plant will normally grow leaves with a point, basil with a sharp point is abnormal. These can be signs of stressors like over-fertilization or too much sunlight. 

Conclusion

While the perfect tender leaves of a basil plant are what we all hope for, sometimes environmental factors will stress the plant into growing curled and distorted leaves. The 9 factors above cover all the bases. Take it step-by-step to remedy the issue, and in no time, you’ll be growing more perfect basil leaves than you know what to do with!