When to plant onions in District of Columbia
District of Columbia’s average last spring frost is April 10, and the first fall frost typically arrives around October 25 — about 198 frost-free days (USDA zones 7a, 7b, 8a). Onion needs 90–120 days to mature, which fits comfortably within District of Columbia's growing season.
When to plant onions in District of Columbia: the short answer
For a spring planting, plant out Mar 13 – Mar 30, with seeds started indoors Jan 23 – Feb 6. Seeds germinate in soil from 40 to 90°F.
Windows are ~1–2 week bands around each date. Frost dates are a statewide average from NOAA/NCEI normals; your town may differ by two weeks or more. Calendar year 2026.
How to grow onions in District of Columbia, step by step
- Start seeds indoors (Jan 23 – Feb 6). Sow seeds ½ inch deep in seed-starting mix under bright light. They take 7-14 days to sprout, fastest in soil around 70°F. Harden seedlings off for a week before they go outside.
- Prepare the bed. They need at least six to eight hours of direct sun a day and loose soil at least 12 inches deep, with a pH between 6.0 and 7.0. Dig in compost before planting.
- Plant out (Mar 13 – Mar 30). Space plants about 4 inches apart in rows 12 inches apart. It handles frost well, so it can go out before the last frost date. As a cool-season crop it does best before summer heat arrives in District of Columbia.
- Water and feed. Give it steady, even moisture, about an inch of water a week from rain or the hose.
- Watch for pests and problems. Pests: onion maggot, onion thrips. Diseases and disorders: downy mildew, white rot, neck rot, purple blotch.
- Harvest (from about Jun 18 – Jul 18). Onion takes 90-120 days to reach harvest. Match the day-length type to your latitude: long-day onions for the north, short-day for the south, day-neutral anywhere. Bulbing is triggered by day length, not calendar date.
Figures come from our crop data; dates use District of Columbia’s average frost dates. More in the full onion growing guide.
Onion planting dates by USDA zone in District of Columbia
District of Columbia spans USDA zones 7a, 7b, 8a. Colder zones, usually higher or further inland, have a later last spring frost and an earlier first fall frost than the state average, so the onion dates shift with them.
When to plant onions in nearby states
| State | Last frost | Plant out |
|---|---|---|
| District of Columbia (this page) | April 10 | Mar 13 – Mar 30 |
| New Jersey | April 20 | Mar 23 – Apr 9 |
| Pennsylvania | May 1 | Apr 3 – Apr 20 |
| Delaware | April 14 | Mar 17 – Apr 3 |
| Maryland | April 14 | Mar 17 – Apr 3 |
| Virginia | April 15 | Mar 18 – Apr 4 |
| West Virginia | May 5 | Apr 7 – Apr 24 |
Questions gardeners in District of Columbia ask
When is the best time to plant onions in District of Columbia?
Plant onion transplants outdoors in District of Columbia between March 13 and March 30. That timing is set by District of Columbia's average last spring frost of April 10.
When should I start onion seeds indoors in District of Columbia?
Start seeds indoors between January 23 and February 6, about 10 weeks before the last frost, so the seedlings are ready to plant out from March 13.
When will onions planted in District of Columbia be ready to harvest?
Planted on time, onions are usually ready from about June 18 to July 18, 90-120 days after transplanting.
When is the last frost in District of Columbia?
On average around April 10, with the first fall frost around October 25 - about 198 frost-free days. Your town may differ by two weeks or more.