Massachusetts · zones 5a–7a
When to plant onions in Massachusetts.
Sow or transplant between Feb 12 to Mar 28 in a typical year, keyed to Massachusetts's median last frost around Apr 22. A second, fall sowing fits Aug 25 to Oct 6. Dates below are state medians; your ZIP code shifts them by days to weeks.
The 2026 windows
Onions dates for a typical Massachusetts season.
1 · Start indoors
Jan 1 to Feb 14
About 6 weeks before set-out. Warm spot, real light.
2 · Set out
Feb 12 to Mar 28
Keyed to the ~Apr 22 last frost. Sow 0.5" deep, 4" apart.
Fall round
Aug 25 to Oct 6
Counted back from the ~Oct 20 first frost.
Harvest
~95 days later
~0.5 lb per plant over ~1 weeks.
Massachusetts spans more than one climate: Zone 6 is the most common zone, but the state runs 5a to 7a. 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.
Massachusetts growing notes
Massachusetts onions want Cape sand more than Berkshire clay.
Long-day country by latitude, but soil decides bulb size
Every onion sold for a Massachusetts garden needs a lot of daylight to start swelling into a bulb, since the state spans roughly 41 to 43 degrees north end to end, solidly inside the long-day band where 14 to 16 hours of summer daylight is what flips that switch; a short-day type bred for a southern latitude is the classic mismatch, since it tries to bulb too early on too little leaf. The harder local variable isn't which long-day variety to buy, it's the soil, because whatever leaf count the plant has grown when that daylight trigger fires is locked in as the finished bulb's ring count.
Cape Cod and the Islands sit on sandy, quick-draining soil that lets onion roots spread with almost no resistance, part of why the Cape built a market-garden reputation supplying Boston generations ago. Inland Berkshire and central Massachusetts gardens on heavier glacial till need that ground broken up and amended before onions go in, or roots stall against compacted layers the way they would in any dense clay.
Feeding sand and till in opposite directions
Sandy Cape ground drains fast enough that nutrients wash through before a shallow-rooted crop like onion can use much of them, so a light, repeated feeding schedule through the leafy growth stage outperforms one heavy application at planting time. Till soil inland holds nutrients longer but needs a couple of inches of compost dug in to keep it from compacting around the swelling bulb.
Massachusetts soil runs acidic across most of the state regardless of which extreme you're gardening in, and onions grow best in a middle pH range; a fall soil test ahead of spring planting is worth doing on either soil type rather than assuming sand needs no correction simply because it drains well.
Curing in a damp New England fall
Bulbs announce themselves when they're ready to pull: the tops topple over and dry down on their own, and from there the crop wants a shaded, breezy spot rather than a sunny patch of yard to finish. Massachusetts autumn weather runs cooler and damper than the interior Midwest, which slows the cure compared to a dry western state but also cuts the risk of scalding bulbs in a hot afternoon.
Give the neck a squeeze after a couple of weeks in that breezy spot: a papery, dry snap under your fingers means the bulb is ready to trim, while anything still spongy needs more time. Store the finished crop somewhere cold and ventilated, since a damp New England basement without airflow rots a batch that cured perfectly well outdoors.
In Massachusetts: watch for
The pests that find onions here.
A middle-length season, about 181 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: Massachusetts gives onions about 181 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 Massachusetts: questions
When should I plant onions in Massachusetts?+
In a typical Massachusetts year, sow onions or set out transplants between Feb 12 to Mar 28, keyed to the state's median last frost around Apr 22. There's also a fall window: Aug 25 to Oct 6. Your exact dates shift with your ZIP code and microclimate.
When do I start onions seeds indoors in Massachusetts?+
Start seeds inside about 6 weeks before set-out: roughly Jan 1 to Feb 14 for a typical Massachusetts season.
What USDA zone is Massachusetts?+
Massachusetts spans zones 5a–7a, mostly zone 6. 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.