Rosemary leaves turn black

Why do Rosemary leaves turn black? Explained with Solutions

You might sometimes be wondering what can make rosemary leaves turn black?

Reasons that can make your rosemary leaves turn black include over-watering, soil with poor drainage, heavy rainfall, heavy humidity, bugs/pests/insects, diseases, shortage of natural light, etc.

Rosemary as a plant is not very demanding. Growing rosemary either indoor or outdoor is relatively easy.

Let us look below the causes for your Rosemary leaves turning black and the solutions that you can implement.

Over Watering

Tips of rosemary leaves can easily turn black due to overhead watering. Apart from this, overhead watering will cause mildew and dark fungal spots on the leaves. Slowly these two will change your fresh greeny leaves into dark black ones.

People may often get confused between Overwatering and Over Head Watering.

When you provide the plant with too much water than what is required, it means Over Watering.

But when water is applied to a plant at a rate greater than its absorbing capacity, it is called over-head watering.

Symptoms

  • Tips turning black
  • Mildew and fungal spots

Damp vegetation imitates humid conditions and will promote mildew. The spores of mildew will spread all over the plant if you sprinkle water over the leaves.

Rosemary leaves will manage the dampness in hot conditions whereas the leaves can hold the water for more time during winters. This will intensify the risk of fungus.

As said above, rosemary is native to Mediterranean regions. The climate of this region is outlined by good sunshine, dry and sandy soil, arid conditions with occasional rainfall.

The fragrance and tang of rosemary will be highest in these conditions. You should try to replicate these conditions for the healthy growth of your rosemary.

Solution for overwatering causing Rosemary leaves to turn black

The above facts indicate to us that rosemary is a plant that grows really well in dry soil.

Rosemary is drought-tolerant. Water your rosemary only when the topsoil is dry. Avoid over-watering to keep your rosemary fresh. Keep the water always minimal.

It is also safe to water at the base of the herb. This way, the water will reach the root section thus reducing the chances of fungal infections.

It is a general and known fact that the rate of evaporation is high during hot summers. Over-watering won’t be a crucial issue during hot periods.

But in winter, the rate of evaporation is low comparatively. Over-watering during these times will lead to fungal attacks.

So, do not sprinkle water over your leaves during the winter season.

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Soil with poor drainage

Another reason your rosemary leaves turn black is inappropriate soil. Rosemary is habituated to dry roots.

Heavy soils retain too much water making your rosemary easily vulnerable to fungal attacks.

When rosemary is grown in rich compost soil, the possibilities of your rosemary rotting and turning black are more. Compost-rich soil retains more water in the roots compared to sandy soils.

Symptoms

  • Rotting
  • Leaves turning black

Solution

Avoid clay soil and heavy compost soil. Always pick sandy and stony soil. You can also alter your potting soil with horticultural sand or grit.

This will enhance the absorbing capacity of the soil thus reducing the moisture level which turns your rosemary black.

Add more sand to your soil during monsoons. This will help your rosemary roots to drain the excess water quickly and stay healthy.

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Heavy Rainfall

If your plant is exposed to heavy rainfall for over a long period, chances are more than the plant gets infected with fungal diseases.

Solution

Shift your rosemary to such a place where it is not exposed to heavy showers.

If you are growing your rosemary outdoors, make sure you water less maybe once in 20 days during monsoons.

High Humidity

High humidity has a straight connection with your rosemary leaves turning black. It stimulates fungal growth.

Solution

Rosemary plant is able to sustain adverse conditions including freezing chillness.  But avoid too high humidity which is not advisable.

Maintain distance between plants row to row, column to column. Provide your shrub enough space to spread. Adequate spacing is very necessary for proper and healthy growth.

Also, ensure proper aeration.

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Bugs/Pests/Insects

Spiders, mites, mealybugs, thrips, whiteflies, spittlebugs are some of the major pests and insects that attack the rosemary plant.

They weaken the plant and turn it black. These insects leave honeydew which leads to the formation of molds.

  • Spider mites look like tiny spiders and suck chlorophyll, water and other nutrients from the rosemary.
  • Mealybugs are tiny insects. They feed on the sap of rosemary.  Male mealybugs does not have wings while female mealybugs have wings. These pests will create havoc particulary when you rosemary in indoors.
  • Thrips look like small black dots and leads to leaf stippling. This makes the leaf tissues die and turn black.
  • Whiteflies are winged insects like mealybugs. They secrete sticky material which leads to black spots.
  • Spittlebugs leave saliva like foam.

Symptoms

  • Plant weakness

Solution

Always monitor your plants for pests and insects, treat them at the right time to avoid damage to the plant.

One simple homemade spray solution would be 2 tbsp of vegetable oil and 2 tbsp of liquid soap in 7 liters of water.

Apply it on your affected spot of the rosemary plant. Ensure your liquid soap does not contain bleach.

Remove insect or pest-infected leaves then and there to save your rosemary from turning black. Disinfect the shears after each cut. This prevents the spreading of mold.

To control mealybugs and spider mites

Use neem oil or horticultural oil to get rid of mealybugs and spider mites.  You can also try petroleum-based horticultural oil and plant-derived oils.

You can also replace eucalyptus oil with neem oil. Add 4 to 5 drops of eucalyptus oil in 1 liter of water and apply to the foliage.

To control whiteflies

Wash whiteflies from crops with jet spray and use predators.

To control spittlebugs

Remove the foamy secretion of spittlebugs by flushing it away with a quick stream of water.

To control thrips

Wash the leaves with a soap and water solution.

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Fungal Diseases

Rosemary is prone to fungal diseases if you overwater it. Leafspot is one such fungal disease. This disease will discolor the leaves and make Rosemary leaves turn black.

Small dots on leaves also is a possibility that indicates the formation of fungal spores. Blight infection is both fungal and bacterial.

Symptoms

  • Discoloration
  • Patchy leaf growth

Solution

  • Ensure aeration and good sunlight.
  • Prune regularly.
  • Keep your infected plants away from the healthy ones.

Try some home remedies for fungal infections.

  • Milk solution – Take one cup of milk and mix it with five cups of water. Combine both and put it in a spray bottle. Apply this spray once in a week. Though it is useful in controlling fungal infections, it won’t destroy each and every type of infection.
  • Baking soda solution – Take 2 tbsp of baking soda, 2 litres of water and few drops of liquid soap. Spray this mixture to your rosemary.

Shortage of natural light

We all know that sunlight plays a very very important role in photosynthesis. It is only through this process plants receive their food and energy.

Rosemary requires at least 10-12 hours of sunlight a day. This requirement is mandatory for it to grow properly.

Low light for a prolonged period can definitely result in your rosemary leaves turning black. Eventually, the whole plant will dry.

Solution

Place your rosemary in a sunny area if you are growing outdoors. If you are growing it indoors, then try to provide artificial garden lights that are available.

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Some more reasons

Extreme cold conditions might be a problem for your rosemary. It belongs to the Mediterranean region of hot summer and mild winter.

Your rosemary plant will start turning black and weaken due to extreme cold conditions.

You have to protect it during winters. Place your rosemary in such an area where the wind is not too much.

Also, you can add around 7 to 8 cms of mulch to the soil in the middle of autumn.

You can also cover your rosemary with a horticultural frost cover without blocking the air circulation when the temperature is too freezing.

Root rot is also one of the common reasons that turn your rosemary leaves black. You can treat this by shearing the infected roots affected leaves and arresting the spread.

Why is growing rosemary in pots an ideal way out?

Because you will have a grip on the soil pattern and do not have to change the soil conditions of the ground that is not appropriate. This will also provide conducive drainage conditions.

Ensure proper drainage is there to let the water out. Make sure the drainage hole is not blocked by soil.

Check the soil for stones or gravels and remove them if any for clearing the blockage.  Appropriate drainage will help the plant to retain the right amount of water.

The leaves may sometimes turn black also because of heat stress. You need to water them at the proper time for their revival.

You watch your plant grow day in and day out. So, your right judgment about your plant plays a vital role.

Do’s and Dont’s for growing Rosemary plant

Dos

  • Check the plant for infection while buying.
  • Use good quality pots with pores for both indoor and outdoor planting.
  • Prune your rosemary plant during spring to avoid crowding.
  • Fertilize regularly.
  • Diagonize fungal infections on time and treat them with eco-friendly fungicides.
  • Water rosemary only once in 2-3 weeks during hot summers and don’t water it during winter as it will receive the water from the environment.
  • Always give water to the rosemary at its base enabling the roots to absorb it.
  • Ensure fresh airflow.
  • Ensure 10-12 hours of sunlight.

Don’ts

  • Don’t sprinkle water over the leaves.
  • Avoid dampy and boggy soils.
  • Avoid overcrowding.

Few more facts and tips

Rosemary is called an ‘upside-down plant’ as it likes dry roots.

Refresh the soil annually so that you give replenished nutrients again and prune roots if necessary.

Pick a pot that matches the size of your plant. You can change the pot and replant your rosemary once they grow larger.

Rosemary loves a trim often. So, prune them regularly. This will help in the early detection of pests and diseases if any and the actions on treatment.

Following these simple measures will definitely help your rosemary grow better and healthy which will automatically keep them fresh and prevent them from turning black.

Conclusion

There are multiple positive reasons that make planting and growing rosemary very cheering. Maintaining them is quite simple.

Protecting rosemary plants from hard frosts and water logging is all you have to do to keep them healthy.

It will provide leaves to you all round the year and the attention it demands is very very little. Is that not something very pleasing?

Hope the above tips and tricks will help you in nurturing your rosemary in the best ways possible.

Happy growing.