Why is My Rosemary Turning Black? (With Best Solutions)

Rosemary is an aromatic shrub that belongs to the family Lamiaceae. The most common reason for rosemary turning black is due to fungal diseases that happen because of the dampness present in the soil surrounding the roots. It also happens due to highly humid weather conditions.

Rosemary Turning Black
Rosemary Turning Black

Rosemary Turning Black: Reasons and Solutions

The leaves of Rosemary turning black is a very common feature and there are several reasons behind this situation. The most common reason is the occurrence of fungal diseases. This is caused because of damp soil surrounding the roots and also because of extremely high humid conditions.

The other reasons are over-watering, soil on which it is planted has very poor drainage, heavy rainfall, insect attacks, and very less sunlight. Apart from these common reasons, there are root rot, Botrytis, black spot, and other fungal pathogens that would also be responsible for the black leaves of rosemary plants.

There are also ways to treat rosemary plants that have black leaves but before that, it is very important to identify the root cause of rosemary leaves turning black.

Fungal Infection

Fungal infection is quite common in rosemary plants which leads the leaves to turn black over time. Rosemary plants are usually stoic hence very less diseases occur that need proper treatment. There are two types of fungal diseases that occur in rosemary plants such as root rot and powdery mildew.

Root rot is very dangerous for rosemary plants as in the majority of cases the plant dies. The signs of this disease are that the plant would become limp and terminal leaves would be there and eventually, the stem would die.

Powdery mildew in rosemary plants generally happens during warm and wet periods. This disease can be identified as a dusting of white fine spores throughout the plant.

The primary cause of root rot in rosemary plants is the roots fail to uptake anymore and are unable to transport necessary nutrients and water to the entire plant. On the other hand, powdery mildew is caused when the plant is in semi-shade condition and the temperature would range from 60 to 80 degrees F.

Fungal Infection of Rosemary
Fungal Infection of Rosemary

Extreme high humidity can cause fungal infections in rosemary plants. Botrytis Cinerea is a fungus that affects the healthy tissues of the rosemary plant and this pathogen sporulation and spread because of moist humid weather conditions.

However, if there is no humidity, the plant would suffer from dehydration. Hence, the right amount of humidity that rosemary needs to grow properly is a humidity level high at 55%+.

The black spots that can be found in rosemary leaves are usually due to mold, overwatering of plants, or mixing too many pesticides. Therefore, the plant needs proper sunlight and also proper soil that has good draining in order to prevent these black spots.

How do you treat fungus on rosemary?

There are two types of fungal infections occurring in rosemary plants. They are root rot and powdery mildew. Though they are quite dangerous with respect to the health of the plant, with proper knowledge these fungal diseases can be treated and the affected plant can be saved.

In order to remove root rot infection, the plant needs to be dug out and the affected roots need to be pruned and the brown foliage needs to be snipped off.

Then the plant is dusted with fungicide powder. However, if it is observed that the complete root section has turned black and mushy, unfortunately, the plant cannot be saved and should be removed.

If the rosemary plant is in a pot or a container, then the plant should be shifted to a new pot filled with fresh potting soil. In this soil, every two weeks, sand or grit and water should be mixed in proper proportion.

In case of powdery mildew infection, the rosemary plant needs to be treated with the help of an organic fungicide spray. Spraying the plant with neem oil helps to treat the fungus in the plants. 

A proper mixture of 3 tablespoons of baking soda along with 1 tablespoon of vegetable oil, a few drops of dish soap liquid, and one gallon of warm water also helps to fight this fungus.

Overhead Watering and Overwatering

Overhead watering and overwatering of rosemary plants is extremely dangerous and it leads to the rosemary plant turning black and eventually limping off. Since rosemary is a Mediterranean herb, the plant is adapted to the condition of the arid region. Hence overwatering is extremely harmful to the growth of rosemary plants.

This is the most common cause of rosemary leaves turning black. Overhead watering is also a wrong method to water the plants and this also causes the leaves to turn black.

Overhead watering results in damp foliage in a persistent manner, which makes the perfect environment for the powdery mildew to grow over the plants and also dark spots on the surface of the leaves.

Overhead Watering and Overwatering
Overhead Watering and Overwatering

The best possible way to water rosemary plants is to add water at the base of the plant at an interval of every 2 to 4 weeks and water only when the surface of the soil is dry. Depending on the dampness of the soil, the amount of water needs to be given to the rosemary plants.

How to Solve This Problem?

Rosemary plants are adapted to arid conditions and don’t need much water to thrive properly. Scaling back the water from the soil helps the roots to dry out completely and hence prevents overwatering. This step also helps to combat serious fungal diseases such as root rot.

Insects, Pests, and Diseases

  • The insects that commonly attack rosemary plants are aphids, leafhoppers, spider mites, spittlebugs, thrips, and whiteflies. It is very important to protect rosemary plants from these insects to grow properly.
  • The diseases that occur from insects are very dangerous and even cause the death of rosemary plants as well. Aphid bugs suck for necessary nutrients making the plants weaker. Thrips cause the rosemary leaves to stipple because at the feeding spot the tissues die as the cells would drain. This would lead to silver patches on the rosemary leaves.
  • Organic insecticidal soaps, neem oil, and horticultural oils would prevent insects and pests to form any diseases on the rosemary plants.
Insects, Pests, and Diseases of Rosemary
Insects, Pests, and Diseases of Rosemary

How to Solve This Problem?

If rosemary plants are affected by insects, it is very important to get rid of them and also to treat the diseases that occur from insects. Aphid bugs are treated with a pressure washer that needs to be sprayed every alternate day.

Organic insecticidal soap is also used to treat aphid bugs. Spittlebugs create saliva-like foam on the rosemary leaves. This needs to be treated by flushing away the bubble waste and any insects that are inside the foam with a stream of water.

Other Reasons

Lack Of Sunlight And How To Solve This Problem?

Sunlight is a very important aspect of the proper growth of rosemary. Too much sunlight is not good for the growth of rosemary plants. On the other hand, a total lack of sunlight is not good for the growth of rosemary plants and would eventually die in course of time. Moreover, sunlight helps to build the strength and immunity of the plant and lack of sunlight would make the rosemary more prone to diseases.

Slow Draining Soil And How To Solve It?

Rosemary grows in the arid region on hillsides that have gritty sandy soil in it. Rosemary plants won’t survive if the soil drains very slowly or would capture excessive moisture. In the soil, if there is the presence of clay or compacted soil it would retain lots of moisture surrounding the roots of the rosemary plants. This condition would finally turn the rosemary leaves to brown and eventually the death of the plant from root rot.

Root Rot and What Is The Solution For It?

Root rot is a fungal disease that would affect rosemary plants which would leading the plants to turn black or brown. Root rot should be treated on time or else it would lead to the death of the plant.

To get rid of root rot, the rosemary plant needs to be dug out and the affected roots to be pruned. However, if the fungal infection is severe, then the complete root structure needs to be discarded.

How do you take care of a rosemary plant Properly?

There are certain steps that need to be followed in order to take care of the rosemary plants properly. The foremost point is that the soil needs to be well-drained and sandy enough and it should grow under 6 to 8 hours of sunlight daily.

Rosemary thrives best in warm temperatures and has a humid environment and is unable to grow in cold temperatures.

Pruning is a very important step in the growth of rosemary plants however more than one-third of the plant should not be trimmed. The growth of the rosemary plants should be propagated through cutting. Because it is a bit difficult to grow rosemary through seeds properly.

Rosemary needs full sunlight to bloom properly with all its aroma and flavor. Rosemary plants also need to be watered properly, every 7 days depending on the temperature.

Frequently Asked Questions (FAQs)

What does Overwatered rosemary look like?

If the rosemary plant is overwatered, the rosemary leaves would turn yellow and then would turn black. Then slowly the leaves would droop and the leaves would fall off.

Can rosemary recover from overwatering?

A rosemary plant can definitely be saved from overwatering if there are roots present that is still alive and yet not affected by root rot. The plant needs to be dig off and the affected dead roots need to be discarded.

Does rosemary like the full sun?

Rosemary plants grow best when planted in full sunlight. Therefore, the soil should be properly drained as the rosemary plant won’t grow properly on a damp surface with a pH level of 6 to 7.

Can you save a rosemary plant with root rot?

Yes, the rosemary plant with root rot can be saved by digging out the plant and removing the affected dead roots. However, if the entire root system is affected then it should be completely discarded.

Why does my rosemary have black spots?

The rosemary plants will have black spots due to fungal infection, because of mold, overwatering of plants, or due to pests.

Can you eat rosemary with black spots?

The rosemary can be consumed with black spots and is not harmful but one needs to make sure that it is washed properly before eating however the aroma would not be as strong as fresh rosemary.


Rosemary is an amazing Mediterranean herb that grows in arid temperatures and has an amazing aroma and lots of nutritional benefits. However, proper care needs to be taken for the cultivation of rosemary, or else it would turn black.

In order to save the rosemary turning black, proper sunlight should be maintained and the soil should be properly drained. This would ensure the complete growth of rosemary with its full aroma and glory.

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