Basil Leaves Turning Black – How To Prevent Them Effectively?

Basil is an indispensable ingredient in world cuisine. In the West, it is used as an ingredient to enhance the flavor of dishes. While oriental, use it to make sauces or as a side vegetable.

This herb grows well in hot climates such as Central Africa or Southeast Asia. They are also grown year-round in other regions but are more susceptible to dying.

Basil leaves turning black is one of the most visible signs. This article will show you why and how you can take care of them better. Let’s follow a little bit of this farming experience!

The Common Causes Of Black Spots On Basil

Cold Temperature

Basil is originally an herb that grows in hot climates such as tropical or subtropical. When growing in a temperate climate, it should be kept indoors or in warm temperatures and protected from frost.

If you put this plant outdoors or in cold temperatures, it will die. The dark spots on the leaves will spread until it dies.

Bacterial And Fungal

The disease-carrying water or insects can transfer fungi and bacteria to your plants from disease-carrying water or insects. However, the signs of disease from each type will be different, which you can recognize on the leaves of the following:

  • Colletotrichum: turns it into a dark brown color
  • Septoria: turns it into brown with black edges from light to dark
  • Cercospora: causes tiny black spots on the leaf surface
  • Pseudomonas Cichorii: forms moist brown patches on it and stems


Some pests like to eat basil like aphids, thrips, or spider mites. They often attack a tree when it is weakened or has spread from neighboring trees. You can recognize them when a left has small black spots or are punctured and blackened, eventually falling off.

Nutrient Deficiency/Excess

Although very rare, deficiency or excess nutrients, especially nitrogen, can occur. It causes the left to turn yellow, brown, and black before dying.


Soil for basil to grow well needs to be fresh, porous, and well-drained. If the humidity in the water is too high, it will easily cause the roots to rot and not be able to carry nutrients to the stem. As a result, the stems and leaves will gradually turn black and die due to waterlogging.

Other Factors

In addition to the above reasons, some other causes can cause this phenomenon but rarely can be mentioned, such as:

Homemade insecticides and foliar sprays: most of these are highly acidic and can burn the left if used in large amounts.

Air circulation: pathogens will thrive in cramped environments with poor air circulation. As it grows, it becomes infected, with black or brown spots appearing on the leaves.

How To Prevent Your Basil From Developing Black Spots


Spacing between plants is a great way to increase air circulation, reduce soil moisture, and limit the spread of pathogens. Whether growing them indoors or outdoors, you need to keep each plant a foot away from the other.

The lower foliage will not be obscured, so it receives full sunlight, not wet. In addition, the plants, especially of the same species, spread pathogens faster when placed next to each other. Thus, when you separate them, their exposure is reduced, making it easier for you to localize the spread if any.


Watering the base instead of the leaves will help limit the growth of bacteria. It would be best if you also watered it in the morning so that basil has full photosynthetic conditions. During the evening, the leaves should be dry, avoiding waterlogging.

Soil Conditions

Good soil for growing needs a balance of nitrogen, phosphorus, and potassium, combined with plowing and drying to destroy pathogens. It also needs to be porous and has good drainage, avoiding waterlogged roots unable to absorb nutrients to nourish the plant.

You can grow plants in pots or containers for easy movement when the temperature drops, helping the plant survive and grow better.


The suitable temperature for this plant to grow is from 25 to 30 degrees Celsius. Nonetheless, you can hardly determine this temperature outside, especially in the cold season, with large temperature fluctuations. Therefore, when you intend to sow outside, you need to let the plant harden first or use a pot to move when needed easily.


There are many reasons why basil leaves turning black such as low temperature, fungi, bacteria and pests, lack or excess of nutrients or excess water, etc. To limit their occurrence, you need to pay more attention to the quality of the soil and how to water and arrange the plants.

Once the leaves change color, you should prune them clean and eliminate the root cause to avoid it spreading strongly. In addition, you should also limit the use of highly acidic substances to kill pests so that the leaves do not burn.

George Morgan
Blogging is to writing what extreme sports are to athletics: more free-form, more accident-prone, less formal, more alive. It is, in many ways, writing out loud.