Troubleshooting
Silvery Yarrow problems — and how to fix them
Silvery Yarrow (Achillea clavennae) 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.
Root rot in wet or heavy soil
The number one cause of death in cultivation. Achillea clavennae cannot tolerate waterlogged or poorly drained soil, especially in winter. Plant in raised beds or troughs with gritty, lean soil, and avoid overwatering at all times. Winter wet is far more damaging than frost.
Powdery mildew
In humid conditions with poor air circulation, powdery mildew (Erysiphe spp.) can colonise the foliage. Improve ventilation and avoid overhead watering. Planting in full sun with good air movement is the best preventative. Affected leaves can be treated with a sulphur-based fungicide.
Spreading too aggressively
While more restrained than many yarrows, A. clavennae spreads by rhizomes and can outgrow its allotted space in loose, open soil. Divide every 2–3 years in spring to maintain a tidy clump and rejuvenate flowering. Excess runners can be pulled away and replanted.
Prevent silvery yarrow problems before they start
Most silvery yarrow issues are care-mismatch, not bad luck. Dial in the basics:
Silvery Yarrow problems — FAQ
Why is my silvery yarrow root rot in wet or heavy soil?
The number one cause of death in cultivation. Achillea clavennae cannot tolerate waterlogged or poorly drained soil, especially in winter. Plant in raised beds or troughs with gritty, lean soil, and avoid overwatering at all times. Winter wet is far more damaging than frost.
Why is my silvery yarrow powdery mildew?
In humid conditions with poor air circulation, powdery mildew (Erysiphe spp.) can colonise the foliage. Improve ventilation and avoid overhead watering. Planting in full sun with good air movement is the best preventative. Affected leaves can be treated with a sulphur-based fungicide.
Why is my silvery yarrow spreading too aggressively?
While more restrained than many yarrows, A. clavennae spreads by rhizomes and can outgrow its allotted space in loose, open soil. Divide every 2–3 years in spring to maintain a tidy clump and rejuvenate flowering. Excess runners can be pulled away and replanted.