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Basil Leaves Turning Black? (Reasons and Solutions)

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Last updated on September 23rd, 2022 at 01:13 pm

The Basil plant being heat-loving and very sensitive to environmental changes, exhibits some adverse reactions when it faces unfriendly conditions in its grown environment.

As a result, it may sometimes develop black spots on either side of the leaf.

Also, its leaves may turn black completely. This change causes panic for many cultivators. What could be the cause, and how can you fix them?

The Basil leaves turning black primarily depends on how these environmental and biological challenges have affected the Basil plant.

Several reasons may singly or concurrently cause the leaves of the Basil plant to turn black.

These reasons may include the soil and environmental conditions or the plant’s biological activities, or the plant’s surroundings. Some solutions include spacing, careful monitoring, and correct watering.

Why Are My Basil Leaves Turning Black?

For various reasons, Basil leaves show different colorations, which vary from the typical deep green.

These different color changes accompany other conditions or diseases from which the plant might suffer.

Therefore, the black color to which a Basil plant’s leaves turn could come about for several reasons, ranging from the conditions of the environment in which it is grown or the different bio-environmental factors prevalent in the area.

Some causes of black coloration on Basil leaves are explained below:

1. Bacterial and fungal infections cause Basil leaves to turn black.

If exposed to certain species of fungi and bacteria, Basil plants develop diseases that cause their leaves to turn from deep green to different patches of black.

Fungal infections such as Colletotrichum, Cercospora Leaf Spot, and Septoria infect Basil plants resulting in black coloration of the leaves.

In contrast, Pseudomonas Cichorii is a bacterial infection that causes the leaves and stem of the Basil plant to turn from the standard green color to black.

Therefore, the growth of black substances over the plant leaf surface, which makes the plant change colors, would probably result from a fungal or bacterial infection.

This infection process is gradual, and if no control measures are implemented to mitigate it, it worsens by the day.

2. If you expose Basil plants to frost, their leaf surfaces get blackened by the day, and they may die off.

Because Basil is a herb native to tropical or subtropical, hot climates, exposure to frost or cold temperatures affects them in a pretty lousy manner.

Overnight cold snaps from time to time shock growing Basil plants, and their leaves become black as the cold worsens or becomes consistent.

A warm moist atmosphere is ideal for Basil plants’ growth, production, and sustenance.

3. Pest infestation causes the Basil plant varying levels of harm which manifest in the drastic color change noticed on the leaves of the plants.

When pests such as aphids, thrips, and spiders feed on a  Basil plant, black spots from all over the leaves at the places where these pests punctured them.

If these pests can operate unchecked, these leaves eventually become utterly black and fall off the plant.

These pests spread from nearby infected plants or attack plants already in a weakened or malnourished state.

4. Basil plants suffering from nutrient deficiencies showcase their predicaments through the blackening of leaves.

In this case, Basil leaves change color to black only indicates that these plants suffer from malnourishment.

In most cases, these leaves tend to curl as well, with parts of the leaves dying out while other parts remain alive.

Thus, when other probable causes do not seem to be the correct answer to the question of the blackening of leaves, this might be the circumstance that the plant is silently suffering.

5. Sunburns may be another cause of the blackening of Basil leaves. This action occurs when too much direct sunlight strikes the leaves of plants.

When this happens, there’s excessive heat as a result,

Which accelerates the sun’s effect on the leaves of the Basil plant. Sunburns cause the darkest shade of black on the leaves of plants and primarily affect the leaves’ borders.

Is Basil Bad if the Leaves Are Dark?

Generally, Basil leaves are still beneficial when they get dark, mainly if you find the blackness in a few patches on the surface of the leaves.

But when the leaves become slimy and bring to a point where the plant tastes terrible, you should never consume it.

In the case of a minor sunburn on the surface of the Basil plant leaves or a black coloration resulting from nutrient deficiency, you could still use the Basil leaves for several purposes.

First, they could be sun-dried and used as a dry spice before the leaves are unusable.

Pests, diseases, and colds cause the slimy texture observed on the surface of some blackening Basil plants.

Any Basil plant with this level of damage should be removed from the garden and properly disposed of before it completely breaks out in the entirety of the garden.

Therefore, to a certain degree, Basil plants should not be used when their leaves become entirely black.

How to Keep Basil Leaves From Turning Black?

There are several conditions and circumstances in which a Basil plant’s leaves remain evergreen if kept.

First, the black coloration may be the Basil plant reacting to some unfriendly situations. 

In most cases, the blackened Basil leaves become unhealthy for consumption because microbial and biological growth plagues the plants’ surface.

But the most important thing to keep in mind while growing this herb is to try creating an optimum environment for the growth and comfort of Basil plants.

So, here are several things to keep in mind to avoid the phenomenon of blackening of the Basil leaves:

1. When planting, you should place the Basil plants at least one foot apart to create an aerated environment for the Basil plant to grow at its best. 

This decision would give the plant more growing space and prevent disease outbreaks from spreading much faster to other Basil plants in the fold.

Also, placing the Basil plant in proportionate spaces apart from each other reduces the humidity in the atmosphere.

It, therefore, reduces the probability of disease outbreaks which may cause the blackening of Basil plants.

2. You should water basil plants in the mornings, and the water should be applied to the roots and not the leaves to avoid wetting the leaves and creating an environment for bacteria to thrive.

Bacterial infections that aid in turning Basil leaves to black thrive better in wet and moist environments.

For example, if you wet the Basil plant leaves with water at each instant of watering, the plant would be a suitable harbor for bacteria, which changes the color of the Basil leaves from deep green to black.

Therefore, applying irrigation to the roots of the Basil plant would help check the growth of these microorganisms on the plant.

3. Do not transplant your Basil seedlings too early, especially when there is still some harsh cold.

The Basil is a tropical plant that performs much better in warm climates and environments.

Therefore, transplanting the seedlings of this plant when they are still very tender into cold and harsh environments would make the plant start developing black coloration from an early stage.

This activity would limit the entirety of the growth and development of the Basil plant, and the frost’s effects would cause the leaves of the Basil plant to turn black.

4. Always check your Basil plant for pest infestation. When it comes to pests, time makes the difference.

The problem of pests is entirely unavoidable. So the best way to handle them is to pounce on them the instant you find out they are plaguing your Basil plants.

Pests have several effects on Basil plants. But in this case, their activities produce substances that cloud the surfaces of the Basil leaves, making them turn black.

How to Treat Black Spots on Basil Leaves

The formation of black spots on Basil leaves can be halted or even treated. These spots formed on the leaves reflect a discomfort that the plant suffers.

Here are some ways of treating black spots on Basil leaves:

I. Covering the Basil plants in times of biting cold.

It would be best to cover basil plants with bell jars and tents to preserve them during short-term cold weather.

Cold weather generally accelerates the formation of black spots on Basil plant leaves, so shielding the leaves Basil from the cold helps prevent the blackening of leaves.

II. Trimming down the leaves reduces the surface area on the Basil plant available for attack by adverse conditions.

Before a cold cycle sets in, it is very advisable to harvest the leaves on your Basil plants and preserve or store them so that there’ll be available Basil for future use in case the weather interferes with the productivity of the live plant.

III. Removing the damaged Basil leaves prevents the damage from spreading further if the leaves are affected by pests, bacteria, fungi, or sunburn.

However, certain plant conditions spread swiftly to other plants, interacting with the healthy and infected plants.

So, removing the affected plants from the general population once you notice an unhealthy plant dramatically reduces the risk of all plants getting their leaves stained with black spots.

IV. Keeping the soil moist always helps retain heat in the ground and, therefore, reduces the risk of harboring harmful microorganisms that do not survive in hot environments.

This occurrence prevents the plant from getting infected by these organisms, thus, not getting their leaves blackened.

Other Possible Solutions to Fix Black Basil Leaves?

Basil plants grown indoors before being taken outside should be treated with sunlight gradually until it gets accustomed to the outside environment.

This act is because taking your tender Basil seedlings outside for the first time and exposing them to crazy amounts of sunlight causes sunburn, which results in the black coloration noticed on the surfaces of the Basil leaves.

Also, mulch should be applied when Basil is being grown; it prevents Basil’s leaves from having direct contact with the soil, thus protecting them from hosts of microorganisms that cause blackening.


Although Basil is understood to be resilient, certain environmental factors produce some adverse effects on the plant, one being the black coloration that covers the surface of these Basil leaves.

Experts have explained this blackening has to be caused by a series of reasons which you could tackle with conscious efforts. This article has already equipped you with all that.


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