Troubleshooting
Purity cosmos problems — and how to fix them
Purity cosmos (Cosmos bipinnatus 'Purity') 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.
Stem lodging in wind
Tall, hollow stems are vulnerable to wind damage and lodging, especially in fertile soil. Provide garden cane stakes at 60–75 cm (24–30 in) intervals in exposed sites, or plant in groups where stems support each other.
Botrytis (grey mould)
Grey, fuzzy mould on petals and stems in cool, damp, overcast conditions. Remove affected material immediately, improve air circulation, and avoid wetting foliage. Preventive copper fungicide can be applied in persistently wet seasons.
Slugs on seedlings
Young seedlings are vulnerable to slug damage, especially in cool, wet spring conditions. Apply iron-phosphate slug pellets (safe around pets and wildlife), or use copper tape around containers. Seedlings recover well once established past 10 cm (4 in) tall.
Prevent purity cosmos problems before they start
Most purity cosmos issues are care-mismatch, not bad luck. Dial in the basics:
Purity cosmos problems — FAQ
Why is my purity cosmos stem lodging in wind?
Tall, hollow stems are vulnerable to wind damage and lodging, especially in fertile soil. Provide garden cane stakes at 60–75 cm (24–30 in) intervals in exposed sites, or plant in groups where stems support each other.
Why is my purity cosmos botrytis (grey mould)?
Grey, fuzzy mould on petals and stems in cool, damp, overcast conditions. Remove affected material immediately, improve air circulation, and avoid wetting foliage. Preventive copper fungicide can be applied in persistently wet seasons.
Why is my purity cosmos slugs on seedlings?
Young seedlings are vulnerable to slug damage, especially in cool, wet spring conditions. Apply iron-phosphate slug pellets (safe around pets and wildlife), or use copper tape around containers. Seedlings recover well once established past 10 cm (4 in) tall.