Plant Onions in Zone 5b

Seed-starting, transplant & harvest dates for USDA Zone 5b

Start indoors

Feb 14

Transplant

Apr 11

Harvest (~100d)

Jul 20

Zone 5b averages 166 frost-free days, running from a last spring frost around April 25 to a first fall frost around October 8. Onions needs roughly 100 days from planting out to first harvest, so it uses about 60 percent of that window. Onions is a hardy crop, which is what decides where in the window it belongs.

Because onions needs a head start, sow seed indoors around Feb 14, about 10 weeks ahead of the Zone 5b last frost. Transplants go out around Apr 11. Starting earlier than that in Zone 5b usually backfires: plants outgrow their cells and stall when they finally hit cold soil.

Planting onions for a fall harvest in Zone 5b

Yes. Plant onions between August 27 and September 17 in Zone 5b, roughly 6 to 3 weeks before the average first frost, so it roots before the ground freezes.

Short-day onion sets planted in fall overwinter in zone 7 and warmer and bulb up months ahead of a spring planting.

Plant from

Aug 27

Plant by

Sep 17

Overwinters, harvest in spring

Spring

Fall dates are counted backward from the Zone 5b average first frost, not forward from a sowing date. See the fall planting calendar by zone for the full method.

Spring vs fall onions in Zone 5b

Planting	Sow or start	In the ground	Harvest
Spring	Feb 14	Apr 11	Jul 20
Fall	by Sep 17	Sep 17	Next spring

Last spring frost

Apr 25

First fall frost

Oct 8

Growing season

166 days

Onions in nearby zones

Onions in Zone 5a (colder) Onions in Zone 6a (warmer) Full Onions grow guide Zone 5b planting calendar

Other crops in Zone 5b

Tomatoes in Zone 5b Peppers in Zone 5b Cucumbers in Zone 5b Lettuce in Zone 5b Zucchini in Zone 5b Carrots in Zone 5b Beans (bush) in Zone 5b Peas in Zone 5b Broccoli in Zone 5b Spinach in Zone 5b Kale in Zone 5b Garlic in Zone 5b Potatoes in Zone 5b Squash (winter) in Zone 5b Corn in Zone 5b Radishes in Zone 5b Beets in Zone 5b Eggplant in Zone 5b Basil in Zone 5b Cilantro in Zone 5b Parsley in Zone 5b Pumpkins in Zone 5b Sunflowers in Zone 5b

Frequently asked questions

When should I start onions in Zone 5b?

Start onions seeds indoors around Feb 14 (Zone 5b).

Can I direct sow onions in Zone 5b?

Onions is best started indoors and transplanted in Zone 5b rather than direct sown.

Can I plant onions in the fall in Zone 5b?