8 Causes of Black Leaves on Plants (And How To Fix)

Growing plants is a fascinating and uncomplicated activity. Today it is impossible to imagine a yard without flowers, bushes, and trees. They are all living organisms with which we sometimes have problems.

Inadequate air circulation combined with high humidity creates an ideal environment for the growth of various diseases. This includes both fungal and bacterial infections. If the temperature is also high, large black spots can form on the leaves.

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Overwatering

Overwatering is the cause of many problems with the plant, including the turning of the leaves to black. The thing is that if the roots of the plant are constantly wet, the exchange of air is disturbed and they begin to die off. Root rot follows, which can completely kill the plant.

Depending on the type of plant and the growing conditions, the leaves can turn black, brown, yellow, and even curl. If the plant is growing in a pot you may see mushy roots by pulling it out.

Symptoms:

• Leaves turn black and die off after a while.
• The plant looks weakened.
• The soil near the roots is completely wet for a long period of time.
• The leaves turning black and yellow.

Solution:

• Eliminate the cause of the overwatering.
• Water the plant only when the soil is at least 1 to 2 inches dry.
• If the plant is growing in a pot, make sure there are drainage holes.
• If possible, transplant the plant to a less moist location with drained soil. But do this only in early spring.

Too much fertilizer

The second common cause of blackened leaves is an overabundance of minerals (salts) in the soil. Gardeners often use very nutritious soil and too much fertilizer in an attempt to speed up plant growth. But not all plants are heavy feeders so they can react with a color change.

This is especially true for nitrogen. Large amounts of nitrogen will cause rapid growth of green leaves, they will not mature in time and will be soft. Such leaves are very prone to rot and mildew and if they get infected they will turn black or dark brown. Also, soft leaves can simply turn black and die.

Symptoms:

• The leaves of the plant have large black spots.
• Parts of the leaf turn black and the leaf dies.
• The plant has been fertilized too often.
• The soil in which the plant is growing is saturated with organic matter.
• The leaves turning black and falling off.

Solution:

• If the plant is growing in a pot, water it with plenty of water. This will flush some of the excess salts out of the soil.
• Remove any damaged leaves.
• Fertilize the plant no more than 2-3 times a season.
• If possible, transplant the plant into fresh soil.

Fungal damage

Next comes disease as the cause of black leaves. In fact, plants as well as other living organisms sometimes get sick. You should not ignore this factor because it can lead to the loss of the plant.

Among other diseases, Botrytis Cinerea and powdery mildew turn the leaves black. In the case of powdery mildew, the leaves are also covered with a white coat. Disease development is mainly due to lack of air circulation and high humidity or overwatering.

Symptoms:

• Leaves turn black completely and a white powder is visible on them.
• Leaves get black mold spots.
• The plant is growing in humid conditions with poor ventilation.

Solution:

• Remove the damaged leaves.
• Provide active air exchange.
• Spray the plant with a multi-purpose fungicide or copper-based fungicide.
• Do not overwater the plant.

Lack of phosphorus

Phosphorus takes an active part in the growth of the plant and its deficiency can lead to the blackening of the leaves. This does not happen often, but if the plant lacks phosphorus, the leaves will turn black or purple-black starting from the tips.

The reason for the lack of phosphorus in most cases is too acidic soil. In this type of soil, it is difficult for the plant to absorb phosphorus and it becomes deficient. Adding phosphorus fertilizer alone cannot solve the problem.

Symptoms:

• Leaves turn black starting at the tips or edges.
• Purple-black spots appear on the leaves.
• The soil is too acidic.

Solution:

• Check the pH with special tests available at garden stores or online.
• If the soil pH is less than 5, put some garden lime into the soil around the plant. This will make the soil neutral.
• Then apply phosphate fertilizer according to the instructions on the package.

Late frosts

The optimal temperature for most plants to thrive is 65-80 °F (18-26 °C). Unfortunately, nature is not always predictable and often gives us surprises. Late spring frosts often occur, which can cause the plant to suffer.

If young leaves have been hit by a late frost, they can partially or completely turn black. These leaves will not recover, but if the branches and dormant buds are intact, the plant will recover over time.

Symptoms:

• Leaves of the plant have turned partially or completely black.
• There was a frost the day before.
• In the case of a houseplant, frostbite was caused by proximity to a refrigerator or ice machine.
• The leaves turning black at the tips.

Solution:

• Remove the black leaves.
• Water the plant one additional time.
• Cover your plants when late frost arrives.
• Do not place houseplants close to cooling devices.

Sunburn

Not all plants are the same way about sunlight. Some can withstand all-day direct sun, others need full shade. But even the most sun-loving plants can get black burns.

This often happens if you bought a plant in a nursery where it was growing under dapple sun. When you got home you placed it in full sun, after a while it got burnt. In this case, you need to know exactly how much sun your plant needs and accustom it to the sun gradually.

Symptoms:

• Large, black-colored burns are present on the leaves.
• The plant is placed in full sun all day.
• You have abruptly moved the plant from one location to another sunnier location.
• The leaves turning black and crispy.

Solution:

• Shade the plant or if potted, move it to a more shady location.
• Water the plant once.
• Find out exactly how much sunlight your plant needs.
• When you see that the plant is recovering, accustom it to more light gradually.

Pest infestation

The last possible reason for the leaves turning black is pests, namely aphids. Aphids are insects that are usually found on the upper leaves and young stems of the plant. Their food is the sap of the plant.

Once a colony of aphids has grown to a large size, their sticky excretions cover a large number of the lower leaves. These secretions are a breeding ground for the spores of a fungal disease called sooty mold. Large black spots appear on the leaves where the disease has attacked.

Symptoms:

• Aphids can be found on the upper leaves and stems.
• The lower leaves are covered with sticky secretions and are black in color.
• The blackened leaves are deformed.
• New leaves turning black.

Solution:

• Wash the aphids off with water.
• Spray the plant with horticultural oil (0.5-gallon water + 1 teaspoon dish soap + 2 tablespoons horticultural oil).
• Wash off the sticky secretions and black color if possible.
• Spray the plant with a broad-spectrum fungicide.

High humidity

Most plants can tolerate a fairly wide range of environmental conditions. However, if the humidity is too high, black spots may form on the leaves. This is the result of a disease. The situation is aggravated by poor ventilation and a warm environment.

Symptoms

• There is high humidity and poor air exchange in the place where the plant is growing.
• The environment is quite warm.
• There are large black spots on the leaves.

Solution

• Reduce the humidity to 50-60%.
• Improve air exchange around the crown of the plant.
• Remove the black leaves.
• Treat the plant with a fungicide.

People also ask

How to fix black leaves on plants?

To fix black leaves on a plant you need to do the following steps:

1. Water the plant only when the soil is at least 2 inches dry.
2. Avoid over-fertilizing the plant. Most plants do not need to be fertilized more than twice a year.
3. Provide good air exchange around the plant. If black spots appear on the leaves, spray them with a multi-purpose fungicide.
4. Cover the outdoor plant for late frosts. For indoor plants, eliminate cold drafts.
5. Provide the right amount of sunlight. Some plants need only reflected sunlight while others need direct sun all day.
6. Get rid of pests on your plant. Neem oil can control most plant pests.

Should I cut off black leaves?

You should definitely cut off the black leaves if the cause is a disease. If the leaf is more than half black, you should remove it anyway.

On the other hand, if only the leaf tips or edges are black then don’t rush to cut them off. Wait a while and see what happens next. If the blackening has stopped and a good part of the leaf is green, let it stay.

If you do need to remove the leaves, take a little distance from the trunk or branch. It’s best to cut off in the middle of the leaf petiole. Also, always use a clean, sharp pruning tool.

Why are my plant leaves black?

Causes of black leaves on plants include:

1. Overwatering;
2. Over-fertilization;
3. Fungal diseases;
4. Pests;
5. Frost damage;
6. Sunburn.

Source: https://gardencourte.com
Categories: Outdoor