When to start seeds indoors
Each crop needs a set number of weeks under lights before it goes outside. Type your town and we count back from its average last frost for every crop below.
- Late year (1 in 10)
- May 5
- Early year (1 in 10)
- Apr 4
- First fall frost
- Oct 27
- Frost-free season
- 191 days
NOAA NCEI U.S. Climate Normals 1991-2020 · station Columbus Port Columbus Intl Airport, OH, 6 mi away, 810 ft
Start-indoors dates for Columbus, OH
| Crop | Start seeds indoors | Plant outside |
|---|---|---|
| Onions | Dec 27 to Mar 7 | Mar 7 to Apr 4 |
| Leeks | Jan 3 to Feb 7 | Mar 14 to 21 |
| Celery | Jan 24 to Feb 7 | Apr 4 to 18 |
| Parsley | Jan 24 to Mar 7 | Apr 4 to 18 |
| Kale | Jan 31 to Mar 7 | Mar 14 to 28 |
| Cabbage | Jan 31 to Mar 14 | Mar 14 to Apr 4 |
| Peppers | Feb 7 to Mar 7 | Apr 18 to May 9 |
| Broccoli | Feb 7 to Mar 21 | Mar 21 to Apr 4 |
| Brussels Sprouts | Feb 7 to Mar 21 | Mar 21 |
| Eggplant | Feb 7 to 28 | Apr 25 to May 9 |
| Cauliflower | Feb 14 to Mar 14 | Mar 21 to Apr 18 |
| Marigolds | Feb 21 to Mar 21 | Apr 18 to May 9 |
| Herbs | Feb 21 to Mar 21 | Mar 21 to May 2 |
| Tomatoes | Feb 21 to Mar 7 | Apr 18 to May 2 |
| Lettuce | Feb 28 to Mar 28 | Mar 21 to Apr 18 |
| Swiss Chard | Feb 28 to Mar 14 | Apr 4 to 18 |
| Basil | Feb 28 to Mar 28 | Apr 18 to May 2 |
| Zinnias | Mar 7 to 21 | Apr 18 to May 9 |
| Okra | Mar 14 to 28 | |
| Cucumbers | Mar 21 to Apr 4 | Apr 18 to May 2 |
| Zucchini (Summer Squash) | Mar 21 to Apr 11 | Apr 18 to May 2 |
| Winter Squash | Mar 21 to Apr 11 | Apr 25 to May 9 |
| Pumpkins | Mar 21 to Apr 4 | Apr 25 to May 9 |
| Watermelon | Mar 21 to Apr 11 | Apr 25 to May 9 |
| Cantaloupe | Mar 21 to Apr 11 | Apr 25 to May 9 |
Ranges cover what university extension guides recommend for each crop. Longest indoor time first.
How the count works
Extension guides give the time indoors in weeks before the last frost: onions need 6 to 16 weeks, cantaloupe only 1 to 4. We take your average last frost from the NOAA station nearest you and subtract those weeks. The planting-out column uses the same frost date, later for crops that are hurt by cold and earlier for the hardy ones.
The average last frost is a 50-50 date. If you plant tender crops out early, keep a row cover or an old sheet ready for cold nights, and watch the forecast for the two weeks after it.
Questions
Why count back from the last frost?
Seedlings need a set number of weeks indoors to reach a good size for planting out, and planting out depends on frost. Start too early and plants get tall and weak in the pots; too late and they are small when the season starts.
What if my dates are already past?
Buy young plants instead, or sow a fast crop straight in the garden. For a fall crop, count back from your first frost date instead.
Do I need grow lights?
A bright south window works for some crops, but most seedlings stretch without 12 to 16 hours of strong light a day. Keep lights a few inches above the leaves and raise them as the plants grow.
What is hardening off?
Moving seedlings outdoors for a few hours a day over a week or two before planting, so they get used to sun, wind and cool nights. Skip it and leaves can scorch or plants stall.
Weeks indoors and planting-out times: university extension guides, listed on each crop's page and on the sources page. Frost dates: NOAA NCEI U.S. Climate Normals 1991-2020. General timing; your local extension office has the final word.