Plant Onions in Zone 4a

Seed-starting, transplant & harvest dates for USDA Zone 4a

Start indoors

Mar 1

Transplant

Apr 26

Harvest (~100d)

Aug 4

Zone 4a averages 135 frost-free days, running from a last spring frost around May 10 to a first fall frost around September 22. Onions needs roughly 100 days from planting out to first harvest, so it uses about 74 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 Mar 1, about 10 weeks ahead of the Zone 4a last frost. Transplants go out around Apr 26. Starting earlier than that in Zone 4a usually backfires: plants outgrow their cells and stall when they finally hit cold soil.

Planting onions for a fall harvest in Zone 4a

Yes. Plant onions between August 11 and September 1 in Zone 4a, 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 11

Plant by

Sep 1

Overwinters, harvest in spring

Spring

Fall dates are counted backward from the Zone 4a 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 4a

Planting	Sow or start	In the ground	Harvest
Spring	Mar 1	Apr 26	Aug 4
Fall	by Sep 1	Sep 1	Next spring

Last spring frost

May 10

First fall frost

Sep 22

Growing season

135 days

Onions in nearby zones

Onions in Zone 3b (colder) Onions in Zone 4b (warmer) Full Onions grow guide Zone 4a planting calendar

Other crops in Zone 4a

Tomatoes in Zone 4a Peppers in Zone 4a Cucumbers in Zone 4a Lettuce in Zone 4a Zucchini in Zone 4a Carrots in Zone 4a Beans (bush) in Zone 4a Peas in Zone 4a Broccoli in Zone 4a Spinach in Zone 4a Kale in Zone 4a Garlic in Zone 4a Potatoes in Zone 4a Squash (winter) in Zone 4a Corn in Zone 4a Radishes in Zone 4a Beets in Zone 4a Eggplant in Zone 4a Basil in Zone 4a Cilantro in Zone 4a Parsley in Zone 4a Pumpkins in Zone 4a Sunflowers in Zone 4a

Frequently asked questions

When should I start onions in Zone 4a?

Start onions seeds indoors around Mar 1 (Zone 4a).

Can I direct sow onions in Zone 4a?

Onions is best started indoors and transplanted in Zone 4a rather than direct sown.

Can I plant onions in the fall in Zone 4a?