When to Plant Onion in Pennsylvania

Growing Onion in Pennsylvania: Complete Guide

Onion (Allium cepa) is a warm-season crop that needs a head start indoors before Pennsylvania's last frost. Depending on your zone, Pennsylvania gardeners start seeds indoors between January 23, 2027 (Zone 8a) and March 15, 2027 (Zone 5a), then move transplants outside once their zone's last frost has passed — the zone table above has your exact dates.

Because Pennsylvania stretches across 7 USDA hardiness zones (5a, 5b, 6a, 6b, 7a, 7b, 8a), 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 Pennsylvania'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 Pennsylvania.