6 Reasons for Rosemary Leaves Turning Black [Control & Prevention]

Rosemary is an aromatic perennial shrub of the Mediterranean region. It has been a good pick for gardeners because of its potential health benefits and multiple uses.

Being native to the arid region it’s a bit tricky to grow these spiny beauties in other areas. Some adverse factors can cause destroying your plants starting from turning your leaves black.

The major causes for black leaves on rosemary are overwatering, over-head watering, fungal and insect infestation, and root rot. Multiple climatic conditions can also promote this problem.

Well, Don’t panic! This problem can be solved easily. And we are here to help you with some actionable solutions step by step.

 So, let’s dive in without further ado-

Why are the Rosemary Leaves Turning Black?

1.Overwatering

Let’s start with a common management mistake often done with rosemary.

Basically, rosemary is a shrub of the arid region where the climate is dry with sandy soil. So, in general, it doesn’t need much water.

If you notice your rosemary leaves are turning black, the main reason can be overwatering. Because it encourages fungal diseases. And fungal diseases can come up with other issues like root rot, black spot, botrytis, etc.

Another reason behind this problem can be over-head watering. Tips of rosemary leaves can easily turn black due to this.

Over-head watering can cause mildew and dark fungal spots on your foliage. Gradually both of these will transform your green spiny leaves into dark black ones.

Control Measures

It’s not that hard to deal with overwatering. Just follow these simple management tricks.

Water at the root portion of your plant in every 14 to 28 days.

Well, we have discussed excessive watering issues so far. But what will happen if you have already ended up overwatering and now facing other problems related to this?

Don’t panic. Let’s talk about the solutions while pointing out the major problems.

2.Fungal Attack

Apart from overwatering, the fungal infestation is another complication that causes black leaves in rosemary. 

Let’s discuss some common fungal attacks and try to find solutions for them.

Mildew is a common fungal problem. This causes gray patches on the plant which may promote leaf darkening.  You can notice some whitish-gray fungal growth on plant leaves which may appear on both sides of the leaves.

Another detrimental enemy can be molds. These are mainly caused by insects. Yes, you heard it right. Insects often leave honeydew-like substances on rosemary leaves. This can promote black spots on leaves.

Control Measures

Keep in mind that rosemary is an edible herb. So, choose your fungicide wisely. Here we have suggested some effective ones. Just take a look.

  • Use best copper fungicide specially formulated for herbs like rosemary (our pick: Bonide Copper Fungicide)
  • Take 2 parts of mature compost and incorporate with 10 parts of water. Let this sit for a week or two. Then add water until it reaches a concentration of brewed tea. And apply this on your plant every 2 weeks.
  • Keep your affected plants separated from healthy ones.
  • Remove infected leaves with garden shears. After doing so don’t forget to clean them with rubbing alcohol or phenol-based cleaners to remove fungal residue.
  • If grown in pots, wash the pots with soap water and rinse with 10% diluted bleach before using them for the next batch of rosemary.

Home Remedies for Fungal Treatment

#Recipe 1: Milk solution

Ingredients:

  • 100 ml milk
  • 500 ml water

Steps :

  • Combine both in a spray bottle.
  • Apply this solution to your foliage once in 7 days.
  • A little drawback of milk spray – Though it’s great for restricting fungal outbreaks, milk spray may not be able to destroy all types of fungal growth.

#Recipe 2: Baking soda mixture

Ingredients:

  • 2 tablespoons baking soda
  • 2 liters water
  • Few drops of liquid soap

Steps :

  • Mix baking soda and water according to the ratio.
  • Then add liquid soap.
  • Make a spray out of this solution and apply it to your rosemary plant.

Preventive Measures

Here are some recommendations to avoid fungal attacks.

  • Clean up your garden debris as soon as possible.
  • Provide proper air circulation.
  • Do not encourage overcrowding of plants. Thin out often to avoid this.
  • Avoid overhead watering.
  • Provide proper lighting.

3.Insect Attack

Mites, mealybugs, whiteflies, thrips, etc are the most detrimental pests in rosemary plants. These encourage fungus formation by leaving behind honeydews.

Control Measures

To avoid insect attacks and further diseases, monitor your plants regularly and treat the affected ones. Try to avoid any toxic chemicals for your plants. Here are some of our suggestions. So let’s get down to it.

  • Pick an insecticide formulated for organic farming (our pick: Monterey Garden Insect Spray)
  • Insecticidal soap or neem oils are safe options for your rosemary.

Try petroleum-based horticultural oils or some plant-derived oils i.e. neem oil or canola oil. You can also use commercial insecticidal soaps. Mineral oils present in these soaps effectively control pest attacks. Our recommendations-

  1. Organic Neem Bliss 100% Pure Cold Pressed Neem Seed Oil
  2. Safer Brand Insect Killing Soap Concentrate

You can simply make some insecticidal soap at home. Just mix 2 tablespoons of vegetable oil and 2 tablespoons of liquid soap in 7 liters of water and you are good to go. Apply this with a sprayer on the affected area.

Caution – Don’t use any soap that contains bleach. This can destroy your tiny shrubs.

Home Remedies for Insects

#Recipe 1: Eucalyptus oil

This can be a good replacement for commercial neem oil.

Ingredients:

  • 4 to 5 drops of eucalyptus oil
  • 1 liter water

Steps :

  • Add the eucalyptus oil to water and stir properly.
  • Put it in a spray bottle and apply to the foliage.

#Recipe 2: Chili spray

Ingredients:

  • 2 tablespoons of fresh or powdered chili.
  • 1 liter water.

Steps :

  • Carefully add crushed or powdered chilies in water.
  • Let it sit for some time.
  • Sieve the mixture and transfer the liquid into a spray bottle to use.

Caution – Chili can cause severe eye and nasal irritation. So, be careful while mixing. Use gloves while handling this spray.

4.Root Rot

Root rot can eventually destroy your whole plant. As it starts with the underground portion, you may not be able to detect it at the initial stage.

Root rot is often caused by pythium. The main symptoms include yellowing of leaves, brown branches, and darkly browned to black leaf tips.

Control Measures

The treatment for root rot is a bit different from other fungal attacks. Here we have mentioned some for you.

5.Improper Soil

You may have taken all necessary steps as discussed. But still not being able to find why your rosemary leaves are turning black.

Inappropriate soil can be a reason here. Compact and heavy soils can retain a high amount of water which is a forewarning for fungal growth in rosemary. So, don’t forget to check your soil before planting.

All you can do is

  • Avoid clay soil and soil that is high in compost.
  • Pick sandy and stony soils for rosemary.
  • In case of growing in pots, make sure the drainage hole is not blocked by soil.

6.Some Climatic Factors

Till now we have discussed some plant problems so far. After going through all these you might have observed that some climatic conditions can’t be controlled. Maybe your region is not favorable for rosemary, so what can you do? Think a bit. We are here to help. Keep reading.

High Rainfall

Maybe your outdoor garden is receiving high rainfall for a long period. This can regulate fungal growth as mentioned before.

In this case, all you can do is water your rosemary as little as possible. This can be once in every 21 days or so.

High Humidity

High humidity has a close relation to your rosemary leaves turning black. A humid condition can encourage any kind of fungal outbreak.

To avoid such conditions you can adopt some measures. Here we suggest some.

  •        Maintain row to row and column to column distance.
  •        Don’t let your shrubs to crowd in one place.
  •       Try to provide proper aeration.
  •     Ensure adequate spacing between plants.

Light

Light is an important factor for rosemary. Normally this shrub needs 6 hours of sunlight. So if planted indoor make sure it gets enough light. You can also provide artificial lighting if necessary.

FAQs

Is black rosemary safe?/Is rosemary bad if turned black?

Normally it’s safe to consume black rosemary. Just wash thoroughly before using them. It might not taste as good as the fresh one. So all you can do is dry up and store them for further use.

But if there is a severe infestation of fungus, it’s better to avoid eating them. You can pick the fresh ones from your bush and store them in the refrigerator in this case.

Can you eat rosemary with black spots?

Black spots occur due to fungal growth on rosemary. These don’t do any harm to the human body. But don’t forget to clean them properly before putting them in your dish. You can also cut off the spotted portion from the leaves.

However, people allergic to fungus should never consume infected plant parts. Be careful about this.

Conclusion

In this article, we have tried to come across some common difficulties while growing rosemary. Hope you have got your solutions from the tips and tricks provided here.

Let’s sum up now. Just follow proper management practices as mentioned and monitor your plants for any disease outbreak. These easy steps can save your tiny beauties with a fresh aroma.

Now feed the right fertilizer to the plant, water regularly, and get the fresh rosemary.

Leave a Comment