Are curled leaves permanent?

Usually, yes. The existing leaves likely won't uncurl, but new growth should be healthy once the stressor is removed.

Should I cut off the curled leaves?

You can trim them if they look unsightly, but wait until you have treated the underlying cause so you do not stress the plant further.

Why are my Ballota nigra leaves curling? Causes and fixes

Check these first

Look closely at the undersides of the curled leaves for small bugs.
Check the soil moisture to see if the plant is dehydrated.
Observe if the curling happens only during the hottest part of the day.

Likely causes

Aphid Infestation
Most likely
How to tell: You see tiny green or black insects clustering on the new growth and the undersides of leaves. The leaves look distorted or curled as they grow.
What to do: Spray the plant with a strong stream of water to knock the aphids off. For persistent cases, apply insecticidal soap or neem oil every 5 to 7 days until they are gone.
Heat Stress
Possible
How to tell: The leaves curl inward during the hottest part of the day to conserve moisture. The plant looks better in the evening when temperatures drop.
What to do: Provide a bit of afternoon shade if the plant is in a very hot location. Ensure the plant is watered deeply every 7 to 14 days to keep the root zone cool.

Curling leaves on other plants

Find out what's wrong with your black horehound

The list above covers the usual causes. Pocket Botanist looks at a photo of your actual plant and tells you the likely cause, how serious it is, and what to try first. Identification and a health check are free.

When to worry

If the curling is accompanied by sticky residue or yellowing, you have a pest problem that needs immediate attention. It is normal for leaves to curl slightly if the plant is temporarily wilting in extreme afternoon heat.

Stopping it coming back

Keep the plant healthy with proper watering and inspect the foliage weekly for early signs of aphids.

Black horehound: curling leaves? Check yours with a photo

Every plant is a little different. Take a photo of your black horehound and Pocket Botanist tells you which cause is most likely, how serious it is, and what to try first. A few checks a day are free. Save the plant and you get care reminders timed for it.

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Questions people ask

Are curled leaves permanent?: Usually, yes. The existing leaves likely won't uncurl, but new growth should be healthy once the stressor is removed.
Should I cut off the curled leaves?: You can trim them if they look unsightly, but wait until you have treated the underlying cause so you do not stress the plant further.

Guides to these causes

Aphids

Why are my Ballota nigra leaves curling?

Check these first

Not sure what's wrong with your black horehound?