Troubleshooting
Costmary problems — and how to fix them
Costmary (Tanacetum balsamita) is generally forgiving once you match its basics, but a few issues come up again and again. Here is what each one looks like, why it happens, and the fix.
Invasive spreading
Rhizomes spread vigorously and the clump can colonise beds. Plant where it can roam, or contain it in a buried pot or root barrier and divide regularly.
Rust and powdery mildew
Crowded, humid plantings develop orange rust pustules or white mildew. Thin and divide clumps, improve airflow, and remove affected leaves.
Sparse or no flowering
In shade or cool conditions costmary often stays leafy and rarely blooms. Give it full sun for flowers, though foliage is the main crop anyway.
Rhizome rot in wet ground
Heavy, waterlogged soil rots the spreading roots. Plant in free-draining soil and avoid overwatering established clumps.
Prevent costmary problems before they start
Most costmary issues are care-mismatch, not bad luck. Dial in the basics:
Looking for costmary in general rather than its problems? Read the full costmary care guide — light, water, soil and feeding.
Costmary problems — FAQ
Why is my costmary invasive spreading?
Rhizomes spread vigorously and the clump can colonise beds. Plant where it can roam, or contain it in a buried pot or root barrier and divide regularly.
Why is my costmary rust and powdery mildew?
Crowded, humid plantings develop orange rust pustules or white mildew. Thin and divide clumps, improve airflow, and remove affected leaves.
Why is my costmary sparse or no flowering?
In shade or cool conditions costmary often stays leafy and rarely blooms. Give it full sun for flowers, though foliage is the main crop anyway.
Why is my costmary rhizome rot in wet ground?
Heavy, waterlogged soil rots the spreading roots. Plant in free-draining soil and avoid overwatering established clumps.