When to Plant Onion in Connecticut

Growing Onion in Connecticut: Complete Guide

Onion (Allium cepa) is a warm-season crop that needs a head start indoors before Connecticut's last frost. Most Connecticut gardeners begin seeds indoors around Wednesday, February 18, 2026 and move transplants outside around Wednesday, April 29, 2026, after the risk of frost has passed.

Because Connecticut stretches across 4 USDA hardiness zones (6a, 6b, 7a, 7b), planting windows can shift by as much as two to four 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 Connecticut'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 Connecticut.