Pocket Botanist
Check these first
- Inspect the undersides of the leaves for orange dust or bumps.
- Check if the soil is staying too soggy for too long.
- Look for signs of poor airflow around the plant base.
Likely causes
Rust fungus
Most likelyHow to tell: You will see small orange or brown pustules on the undersides of the leaves. The leaves may eventually yellow and fall off.
What to do: Remove and destroy all infected leaves immediately to stop the spread. Improve air circulation around the plant and avoid wetting the foliage when you water.
Leaf spot disease
PossibleHow to tell: These appear as dark brown or black spots with yellow halos. They often show up when the plant stays wet for too long.
What to do: Prune away the affected stems and leaves. Water only at the base of the plant to keep the leaves dry.
Find out what's wrong with your square-stalked st. john's-wort
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.
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When to worry
Worry if the spots are spreading rapidly to new growth or if the plant is losing most of its leaves. A few spots on older leaves are common in humid weather.
Stopping it coming back
Water only at the soil level and keep the plant in a spot with good air movement.
Square-stalked St. John's-wort: spots? Check yours with a photo
Every plant is a little different. Take a photo of your square-stalked st. john's-wort 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.
Scan with your phone's camera to get the app
Or go to pocketbotanist.app/get on your phone
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Questions people ask
- Can I save leaves that have spots?
- It is best to remove them. Once the fungus takes hold, the leaf cannot recover and will only spread spores to healthy parts of the plant.
- Will these spots kill my plant?
- Usually not, but it will weaken the plant significantly. If left untreated, the plant may lose so much foliage that it struggles to grow.
Guides to these causes
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Back to the Square-stalked St. John's-wort guide
This article was generated with AI on from the plant’s care profile and is general information, not horticultural advice. Read about how we build these guides.