Growing onions in zone 3
Bulbing is triggered by day length: long-day varieties for the North, short-day for the South, intermediate in between — the wrong type simply won’t bulb. Sets are easiest; transplants give bigger bulbs.
Zone 3 covers northern Minnesota and North Dakota, northern Maine, high mountain valleys — roughly 120 frost-free days — start warm-season crops indoors, lean on cool-season crops. Zone dates are medians: frost timing varies within a zone with elevation and terrain, so treat these windows as a solid default and refine them with your own city’s dates below.
Make it local
These windows use zone 3's typical frost dates (last frost ~May 15, first frost ~Sep 20). For windows computed from your frost dates, run the ZIP code frost lookup and open the planting calendar — it remembers your city. The seed starting scheduler turns the whole seed rack into one printable, date-sorted list.
Frequently asked questions
When do I plant onions in zone 3?
Transplant Apr 3 – Apr 17, counted from zone 3's typical last frost around May 15. As a hardy crop it tolerates the light frosts on either side of that window.
When should I start seeds indoors for onions in zone 3?
Sow indoors Mar 6 – Mar 20 — that's 10 to 8 weeks before the typical May 15 last frost, giving sturdy transplants exactly when the garden is ready for them.
Can I direct sow onions in zone 3?
Yes — direct sow Apr 17 – May 1. Transplants buy a head start, but direct-sown plants catch up quickly once soil warms.