When to Plant Onion in New Hampshire

Growing Onion in New Hampshire: Complete Guide

Onion (Allium cepa) is a warm-season crop that needs a head start indoors before New Hampshire's last frost. Depending on your zone, New Hampshire gardeners start seeds indoors between February 18, 2027 (Zone 6b) and March 20, 2027 (Zone 4a), then move transplants outside once their zone's last frost has passed — the zone table above has your exact dates.

Because New Hampshire stretches across 6 USDA hardiness zones (4a, 4b, 5a, 5b, 6a, 6b), planting windows can shift by as much as six to eight weeks from one end of the state to the other. Gardeners in the warmer southern zones can start earlier, while those in cooler northern zones should wait until the zone table above shows their last frost has passed.

With 100 days to maturity, Onion needs the indoor head start that New Hampshire's growing season requires. Starting indoors ensures you have strong transplants ready the moment outdoor conditions are right.

Onion requires full sun (6+ hours) and moderate moisture. In the Northeast, cool summers and moderate humidity can slow warm-season crops, so choose a sheltered, south-facing spot to maximise heat.

For the most precise planting dates tailored to your exact location, enter your ZIP code on our planting calendar or use the zone table above to find the schedule for your area of New Hampshire.