When to plant cosmos
annual
The short answer
Cosmos are planted out or sown outdoors after the last frost. Start them indoors 3 to 4 weeks before the last frost.
Zone 5: plant out or sow from Apr 30. Zone 7: plant out or sow from Apr 5. Zone 9: plant out or sow from Feb 20. See every zone or your state.
When to plant cosmos by USDA zone
Dates are worked out from each zone’s typical last frost, using the number of weeks the cited extension services give. Find your zone on the zone map. Zones 11 and above are frost-free, so timing there depends on heat and rain instead.
| Zone | Typical last frost | Start seed indoors | Plant out or sow |
|---|---|---|---|
| Zone 3 | May 15 | Apr 17 – Apr 24 | from May 15 |
| Zone 4 | May 10 | Apr 12 – Apr 19 | from May 10 |
| Zone 5 | Apr 30 | Apr 2 – Apr 9 | from Apr 30 |
| Zone 6 | Apr 15 | Mar 18 – Mar 25 | from Apr 15 |
| Zone 7 | Apr 5 | Mar 8 – Mar 15 | from Apr 5 |
| Zone 8 | Mar 20 | Feb 20 – Feb 27 | from Mar 20 |
| Zone 9 | Feb 20 | Jan 23 – Jan 30 | from Feb 20 |
| Zone 10 | Jan 30 | Jan 2 – Jan 9 | from Jan 30 |
Rule used: plant out or sow after the last frost; start seed indoors 3 to 4 weeks before the last frost.
When to plant cosmos in your state
Same rule, applied to each state’s typical last spring frost. States marked * span very different climates, so use your own frost date for the exact day - click a state for its frost dates.
| State | Typical last frost | Start seed indoors | Plant out or sow |
|---|---|---|---|
| Alabama | Mar 25 | Feb 25 – Mar 4 | from Mar 25 |
| Alaska * | May 17 | Apr 19 – Apr 26 | from May 17 |
| Arizona * | Mar 15 | Feb 15 – Feb 22 | from Mar 15 |
| Arkansas | Apr 3 | Mar 6 – Mar 13 | from Apr 3 |
| California * | Feb 20 | Jan 23 – Jan 30 | from Feb 20 |
| Colorado | May 5 | Apr 7 – Apr 14 | from May 5 |
| Connecticut | Apr 25 | Mar 28 – Apr 4 | from Apr 25 |
| Delaware | Apr 14 | Mar 17 – Mar 24 | from Apr 14 |
| District of Columbia | Apr 10 | Mar 13 – Mar 20 | from Apr 10 |
| Florida | Feb 12 | Jan 15 – Jan 22 | from Feb 12 |
| Georgia | Mar 25 | Feb 25 – Mar 4 | from Mar 25 |
| Idaho | May 10 | Apr 12 – Apr 19 | from May 10 |
| Illinois | Apr 20 | Mar 23 – Mar 30 | from Apr 20 |
| Indiana | Apr 24 | Mar 27 – Apr 3 | from Apr 24 |
| Iowa | Apr 25 | Mar 28 – Apr 4 | from Apr 25 |
| Kansas | Apr 15 | Mar 18 – Mar 25 | from Apr 15 |
| Kentucky | Apr 18 | Mar 21 – Mar 28 | from Apr 18 |
| Louisiana | Mar 5 | Feb 5 – Feb 12 | from Mar 5 |
| Maine | May 14 | Apr 16 – Apr 23 | from May 14 |
| Maryland | Apr 14 | Mar 17 – Mar 24 | from Apr 14 |
| Massachusetts | Apr 24 | Mar 27 – Apr 3 | from Apr 24 |
| Michigan | May 10 | Apr 12 – Apr 19 | from May 10 |
| Minnesota | May 6 | Apr 8 – Apr 15 | from May 6 |
| Mississippi | Mar 20 | Feb 20 – Feb 27 | from Mar 20 |
| Missouri | Apr 15 | Mar 18 – Mar 25 | from Apr 15 |
| Montana | May 15 | Apr 17 – Apr 24 | from May 15 |
| Nebraska | Apr 30 | Apr 2 – Apr 9 | from Apr 30 |
| Nevada * | Apr 20 | Mar 23 – Mar 30 | from Apr 20 |
| New Hampshire | May 13 | Apr 15 – Apr 22 | from May 13 |
| New Jersey | Apr 20 | Mar 23 – Mar 30 | from Apr 20 |
| New Mexico * | Apr 20 | Mar 23 – Mar 30 | from Apr 20 |
| New York * | May 1 | Apr 3 – Apr 10 | from May 1 |
| North Carolina | Apr 5 | Mar 8 – Mar 15 | from Apr 5 |
| North Dakota | May 15 | Apr 17 – Apr 24 | from May 15 |
| Ohio | Apr 25 | Mar 28 – Apr 4 | from Apr 25 |
| Oklahoma | Apr 1 | Mar 4 – Mar 11 | from Apr 1 |
| Oregon * | Apr 20 | Mar 23 – Mar 30 | from Apr 20 |
| Pennsylvania | May 1 | Apr 3 – Apr 10 | from May 1 |
| Rhode Island | Apr 25 | Mar 28 – Apr 4 | from Apr 25 |
| South Carolina | Mar 25 | Feb 25 – Mar 4 | from Mar 25 |
| South Dakota | May 10 | Apr 12 – Apr 19 | from May 10 |
| Tennessee | Apr 10 | Mar 13 – Mar 20 | from Apr 10 |
| Texas * | Mar 15 | Feb 15 – Feb 22 | from Mar 15 |
| Utah | May 5 | Apr 7 – Apr 14 | from May 5 |
| Vermont | May 14 | Apr 16 – Apr 23 | from May 14 |
| Virginia | Apr 15 | Mar 18 – Mar 25 | from Apr 15 |
| Washington * | Apr 20 | Mar 23 – Mar 30 | from Apr 20 |
| West Virginia | May 5 | Apr 7 – Apr 14 | from May 5 |
| Wisconsin | May 10 | Apr 12 – Apr 19 | from May 10 |
| Wyoming | May 20 | Apr 22 – Apr 29 | from May 20 |
What extension services say
- Start cosmos seed indoors 4 weeks before the average frost-free date; Colorado also marks cosmos as suited to direct seeding in the garden. Colorado State University Extension ↗
- Minnesota's calendar: mid-April, 3-4 weeks indoors. University of Minnesota Extension ↗
- Missouri's calendar: mid-April, 5 days to germinate, a crop time of 4-6 weeks and a 65°F growing temperature. University of Missouri Extension ↗
- Annual flowers are usually planted in spring as soon as the danger of frost has passed. University of Missouri Extension ↗
- UF/IFAS: make sure the danger of frost has passed before sowing seed outside; germination is best when the soil is 70-75°F; do not plant deeper than about 1/8 inch. UF/IFAS Gardening Solutions ↗
- Cosmos blooms anytime between spring and fall, usually 2-3 months after planting. UF/IFAS Gardening Solutions ↗
Colorado marks cosmos as best direct-seeded two weeks before its frost-free date. We show the later date because Missouri says annuals are planted once frost danger has passed.
Questions gardeners ask
When do you plant cosmos?
Start seed indoors about 4 weeks before the last frost (Colorado State), or sow outdoors once frost danger has passed.
How fast do cosmos grow from seed?
Missouri Extension lists 5 days to germinate and a crop time of 4-6 weeks indoors.
How deep do you plant cosmos seeds?
UF/IFAS says to rake loose seed into the soil and not plant deeper than about 1/8 inch, once the danger of frost has passed and the soil is 70-75°F.
Sources
- University of Missouri Extension: Starting Plants Indoors From Seeds (G6570)
- UF/IFAS Gardening Solutions: Cosmos
- Colorado State University Extension: Growing Annual Plants from Seed
- University of Minnesota Extension: Starting seeds indoors
- University of Missouri Extension: Herbaceous Ornamentals (MG9)
Extension advice is local to the state that wrote it. Where the sources differ, both are shown. Dates in the tables are estimates from typical frost dates; your garden’s own last frost can differ by a week or more. How we source data.