When to Plant Onion in Missouri

Growing Onion in Missouri: Complete Guide

Onion (Allium cepa) is a warm-season crop that needs a head start indoors before Missouri's last frost. Most Missouri gardeners begin seeds indoors around Friday, February 13, 2026 and move transplants outside around Friday, April 24, 2026, after the risk of frost has passed.

Because Missouri stretches across 6 USDA hardiness zones (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 Missouri'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. Midwest growing seasons are compressed between late spring frosts and fall cold snaps, so timing transplants precisely pays off.

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 Missouri.