Troubleshooting
Yarrow problems — and how to fix them
Yarrow (Achillea millefolium) 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.
Aggressive rhizomatous spread
Spreads quickly by underground runners and can swamp neighbours; divide regularly or plant where it can roam freely.
Flopping stems
Tall cultivars splay open in rich soil or shade; grow lean and sunny, or support, and cut back after first flowering for sturdier regrowth.
Powdery mildew
Grey foliar coating develops in humid, crowded conditions; improve airflow, avoid overhead watering and cut back affected growth.
Toxic to grazing animals
Contains glycoalkaloids and lactones that cause GI upset and dermatitis in pets and livestock; site away from animal areas.
Prevent yarrow problems before they start
Most yarrow issues are care-mismatch, not bad luck. Dial in the basics:
Looking for yarrow in general rather than its problems? Read the full yarrow care guide — light, water, soil and feeding.
Yarrow problems — FAQ
Why is my yarrow aggressive rhizomatous spread?
Spreads quickly by underground runners and can swamp neighbours; divide regularly or plant where it can roam freely.
Why is my yarrow flopping stems?
Tall cultivars splay open in rich soil or shade; grow lean and sunny, or support, and cut back after first flowering for sturdier regrowth.
Why is my yarrow powdery mildew?
Grey foliar coating develops in humid, crowded conditions; improve airflow, avoid overhead watering and cut back affected growth.
Why is my yarrow toxic to grazing animals?
Contains glycoalkaloids and lactones that cause GI upset and dermatitis in pets and livestock; site away from animal areas.