When to Plant Onions

Start onions indoors 8 to 10 weeks before your last frost, then plant them out 2 to 4 weeks before your last frost.

Onions at a glance

Start indoors: 8 to 10 weeks before your last frost
Plant out: 2 to 4 weeks before your last frost
Time to harvest: 90 to 120 days from planting out
Harvest lasts: about 4 weeks
Spacing: 9 per square foot
Frost: Takes hard frosts

Growing onions

Onions need full sun, loose rich soil and steady water while the bulbs swell. They do not compete well with weeds, so keep the bed clear. Plant sets or young plants shallow, with the tips just showing, and stop watering once the tops start to fall.

Dates by hardiness zone

Typical dates for each zone; your ZIP code gives your own.

When to plant onions in each USDA hardiness zone
Zone	Start indoors	Plant out	Harvest
Zone 3a	Mar 19 – Apr 2	Apr 30 – May 14	Jul 29 – Sep 11
Zone 3b	Mar 8–22	Apr 19 – May 3	Jul 18 – Aug 31
Zone 4a	Mar 3–17	Apr 14–28	Jul 13 – Aug 26
Zone 4b	Feb 27 – Mar 13	Apr 10–24	Jul 9 – Aug 22
Zone 5a	Feb 22 – Mar 8	Apr 5–19	Jul 4 – Aug 17
Zone 5b	Feb 20 – Mar 6	Apr 3–17	Jul 2 – Aug 15
Zone 6a	Feb 18 – Mar 4	Apr 1–15	Jun 30 – Aug 13
Zone 6b	Feb 12–26	Mar 26 – Apr 9	Jun 24 – Aug 7
Zone 7a	Feb 5–19	Mar 19 – Apr 2	Jun 17 – Jul 31
Zone 7b	Jan 25 – Feb 8	Mar 8–22	Jun 6 – Jul 20
Zone 8a	Jan 18 – Feb 1	Mar 1–15	May 30 – Jul 13
Zone 8b	Jan 6–20	Feb 17 – Mar 3	May 18 – Jul 1
Zone 9a	Dec 22 – Jan 5	Feb 2–16	May 3 – Jun 16
Zone 9b	Nov 23 – Dec 7	Jan 4–18	Apr 4 – May 18
Zone 10a	Nov 15–29	Dec 27 – Jan 10	Mar 27 – May 10
Zones 10b–11b	Frost is rare here, so grow onions in the cooler months, from fall to early spring.