DibbleGrowing cosmos: from seed to harvest
Sow cosmos once the soil is warm and the weather is settled, in lean soil: too much fertility means leaves, not flowers. Deadhead for continuous bloom.
Planting dates for cosmos by zone
| Zone | Start seeds indoors | Sow or transplant | Harvest |
|---|---|---|---|
| Zone 3 | not needed | June 8 | August 17 |
| Zone 4 | not needed | May 31 | August 5 |
| Zone 5 | not needed | May 23 | July 27 |
| Zone 6 | not needed | May 17 | July 28 |
| Zone 7 | not needed | May 1 | July 10 |
| Zone 8 | not needed | April 7 | June 11 |
| Zone 9 | not needed | March 15 | May 18 |
| Zone 10 | not needed | March 18 | April 17 |
| Zone 11 | not needed | January 1 | March 12 |
Each date is the start of the best window from the same climate engine the Dibble app uses, run at typical places in each zone. Dibble tunes them to your garden's own location and lets you adjust frost dates for your own yard.
Companion plants
Good neighbors for Cosmos:
Family and rotation
Cosmos is in the asters family. Lettuce and many flowers. Marigolds and zinnias are excellent companions throughout the garden. Learn about crop rotation.
Related crops
Lettuce
When to plantDahlia
When to plantZinnia
When to plantSunflower
When to plantMarigold
When to plantCalendula
When to plant
Questions
When should I plant cosmos?
It depends on your zone. Cosmos is a tender crop, so the timing follows your last spring frost. Look up your zone in the table below for exact start, sow, and harvest dates, or open Dibble and set where your garden is to get your own calendar.
How long does it take to grow cosmos?
About 70 days from sowing to the first harvest, with a picking window of roughly 70 days after that.
What grows well with cosmos?
Good companions include Zinnia, Sunflower.
Plant at the right time this season
Dibble builds your calendar in under a minute. Free to start, no account needed.