Troubleshooting
Square-stalked St John's-wort problems — and how to fix them
Square-stalked St John's-wort (Hypericum tetrapterum) is generally low-drama, but a few issues come up again and again. Here is what each one looks like, why it happens, and the fix.
Fungal leaf spot and blight in stagnant conditions
Although it tolerates wet soil, stagnant, poorly oxygenated water around the crown can trigger fungal rots — ensure there is some water movement or periodic soil aeration.
Aphids on young growth
Soft new shoots in spring can attract aphid colonies; knock off with a strong water jet or apply insecticidal soap, avoiding spray drift into pond water.
Prevent square-stalked st john's-wort problems before they start
Most square-stalked st john's-wort issues are care-mismatch, not bad luck. Dial in the basics:
Square-stalked St John's-wort problems — FAQ
Why is my square-stalked st john's-wort fungal leaf spot and blight in stagnant conditions?
Although it tolerates wet soil, stagnant, poorly oxygenated water around the crown can trigger fungal rots — ensure there is some water movement or periodic soil aeration.
Why is my square-stalked st john's-wort aphids on young growth?
Soft new shoots in spring can attract aphid colonies; knock off with a strong water jet or apply insecticidal soap, avoiding spray drift into pond water.