Last year I sowed cosmos seeds and had the most amazing display of flowers. They self-seeded all over the garden but this year, they have grown leaves very vigorously and I now have a jungle of flowerless cosmos plants. Why didn’t they flower? Thanks for your thoughts!
- Janelle Bauer asked 1 month ago
If your plants have self-seeded, it’s possible they’re growing where they don’t receive a
minimum of 6 hours of sunlight. Cosmos need at least 6 hours of direct sun to bloom well. Anything less encourages tall, leggy growth with few or no flowers.
Cosmos also actually prefer hot, dry conditions. Too much water leads to vigorous leaf
growth at the expense of flowers.
The other possibility is there’s too much nitrogen in the soil. If your soil has compost, manure, or fertiliser high in nitrogen, cosmos respond by producing heaps of foliage but no blooms.
Then there’s seasonal timing; Cooler or inconsistent weather (common in Melbourne
summers) can delay flowering. Cosmos bloom faster in consistently warm, dry
conditions. What you can do to remedy this is to cut back the cosmos by half. This will encourage branching and new flowering stems. .
If you think there’s too much nitrogen, add a side dressing of potash.
Only water when the soil is dry. If they’re shaded by nearby plants or structures, consider trimming nearby growth if practical.
Once conditions improve, cosmos usually begin flowering within 2–4 weeks. They’re
fast responders once stress factors are removed.
Other gardeners have reported similar occurrences. In many districts, dahlias and
zinnias are only just getting going, and the season is nearly over. Your cosmos is
certainly healthy
- Steven McLean answered 4 weeks ago
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