Washington DC · zones 7b–7b
When to plant onions in Washington DC.
Sow or transplant between Jan 26 to Mar 11 in a typical year, keyed to Washington DC's median last frost around Apr 5. A second, fall sowing fits Sep 13 to Oct 25. Dates below are state medians; your ZIP code shifts them by days to weeks.
The 2026 windows
Onions dates for a typical Washington DC season.
1 · Start indoors
Dec 15 to Jan 28
About 6 weeks before set-out. Warm spot, real light.
2 · Set out
Jan 26 to Mar 11
Keyed to the ~Apr 5 last frost. Sow 0.5" deep, 4" apart.
Fall round
Sep 13 to Oct 25
Counted back from the ~Nov 8 first frost.
Harvest
~95 days later
~0.5 lb per plant over ~1 weeks.
Washington DC spans more than one climate: Zone 7 is the most common zone, but the state runs 7b to 7b. That's why the planner works from your ZIP code's frost dates, not your zone: mountain and coastal gardens in the same state can be three weeks apart.
In Washington DC: watch for
The pests that find onions here.
A middle-length season, about 217 frost-free days, means onion, bulb overlaps onion thrips for a stretch each summer. Check plants every week or two and treat early.
Silvery streaks and curled leaf tips in hot spells.
Organic fix: Insecticidal soap or neem; hang sticky traps.
Seedlings wilt; white maggots in the bulb base.
Organic fix: Float a row cover over the row; rotate beds each year.
Pale patches with fuzzy gray growth in damp weather.
Organic fix: Space for airflow, water early in the day, spray neem.
White rot
Yellowing and dieback, then wilt; fluffy white mold at the bulb base and roots so rotted the plant lifts straight out.
Organic fix: No cure once it is in the soil. Plant clean stock, never follow onions with onions, and keep infested soil off tools and boots.
Your season math: Washington DC gives onions about 217 frost-free days, and it needs roughly 95 days to a first harvest. It's a one-planting crop, so time that single sowing well.
Planting onions in Washington DC: questions
When should I plant onions in Washington DC?+
In a typical Washington DC year, sow onions or set out transplants between Jan 26 to Mar 11, keyed to the state's median last frost around Apr 5. There's also a fall window: Sep 13 to Oct 25. Your exact dates shift with your ZIP code and microclimate.
When do I start onions seeds indoors in Washington DC?+
Start seeds inside about 6 weeks before set-out: roughly Dec 15 to Jan 28 for a typical Washington DC season.
What USDA zone is Washington DC?+
Washington DC spans zones 7b–7b, mostly zone 7. But frost dates, not zones, set planting time. The free planner uses your ZIP code's actual frost dates.
How many onions plants do I need?+
Depends who you're feeding. The crop page has exact counts per household size, or the free planner does the math for your family in about 60 seconds.