Maine · zones 3b–6a
When to plant onions in Maine.
Sow or transplant between Feb 28 to Apr 13 in a typical year, keyed to Maine's median last frost around May 8. A second, fall sowing fits Aug 12 to Sep 23. Dates below are state medians; your ZIP code shifts them by days to weeks.
The 2026 windows
Onions dates for a typical Maine season.
1 · Start indoors
Jan 17 to Mar 2
About 6 weeks before set-out. Warm spot, real light.
2 · Set out
Feb 28 to Apr 13
Keyed to the ~May 8 last frost. Sow 0.5" deep, 4" apart.
Fall round
Aug 12 to Sep 23
Counted back from the ~Oct 7 first frost.
Harvest
~95 days later
~0.5 lb per plant over ~1 weeks.
Maine spans more than one climate: Zone 5 is the most common zone, but the state runs 3b to 6a. 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.
Maine growing notes
Maine's short season makes storage onions worth the wait.
Long-day country, but the soil needs a fix first
Maine sits far enough north that midsummer daylight runs long enough to trigger long-day onion varieties reliably, the same trigger most of the northern tier depends on. But Maine's soil carries a complication those flatter Midwest states mostly skip: ground built over granite bedrock runs naturally acidic, often testing below pH 5.5 in older gardens, and onions sulk badly below pH 6.0, growing thin necks and small bulbs no matter how well the variety matches the daylight overhead.
Patterson is the long-day storage variety to plant in Maine now; Copra, the name a lot of longtime growers here still reach for out of habit, was pulled from production by the company that bred it and is difficult to find on a seed rack these days. Lime worked into the bed the fall before planting, based on a soil test rather than a guess since over-liming creates its own problems, is the fix; a county extension test costs little and tells you exactly how many pounds per 100 square feet your particular ground needs.
Curing for a root cellar, not just a countertop
Maine's old farmhouses were built with root cellars for a reason, and the onion crop here has always leaned on cold, steady storage to carry a household through winter rather than counting on fresh vegetables from a grocery store an hour's drive from anywhere rural. That tradition still shapes how the crop should be cured: once tops fall over on their own, pull the bulbs and let them dry somewhere shaded and breezy, never in direct sun, which scalds the outer layers before the inside has finished curing properly.
The test for done curing is the neck, not the calendar: squeeze it between two fingers, and when it no longer feels wet or springy but instead papery and stiff, the bulb is ready to store away. Give that curing stage 2 to 3 full weeks rather than rushing it, since a bulb stored too soon rots from the neck down within a month, while a properly cured Patterson bulb will hold in a cool space through most of the winter ahead.
Downy mildew likes Maine's foggy coastal mornings
Downy mildew, not the maggot most guides lead with, is the disease Maine's cool, damp air favors, especially in gardens within a few miles of the coast where morning fog is routine most of the growing season. It shows first as pale, oval patches on the leaf that turn a dull purplish-gray fuzz in humid weather, usually starting on the oldest leaves near the base of the plant, and a patch left unchecked can take down the whole leaf within a week.
Spacing plants a full 4 inches apart, rather than crowding them tighter to fit more in a bed, keeps air moving through the row and is the cheapest defense available to a home gardener. Watering at the soil line in the morning, never overhead in the evening, denies the fungus the standing moisture on leaves it needs to establish; once mildew shows on a leaf, cut that leaf out rather than letting spores sit through a next damp morning.
In Maine: watch for
The pests that find onions here.
A middle-length season, about 152 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: Maine gives onions about 152 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 Maine: questions
When should I plant onions in Maine?+
In a typical Maine year, sow onions or set out transplants between Feb 28 to Apr 13, keyed to the state's median last frost around May 8. There's also a fall window: Aug 12 to Sep 23. Your exact dates shift with your ZIP code and microclimate.
When do I start onions seeds indoors in Maine?+
Start seeds inside about 6 weeks before set-out: roughly Jan 17 to Mar 2 for a typical Maine season.
What USDA zone is Maine?+
Maine spans zones 3b–6a, mostly zone 5. 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.