When to Plant Radishes

Planting time for radishes is set by your frost dates, not by the calendar month. Sow directly in the garden about 4 weeks before your last frost, as soon as the ground is workable. From there it takes roughly 28 days to the first harvest. Radishes is a hardy crop, and it keeps going about 21 days past a light frost, which is what makes a fall crop worth planting. Pick your zone below for exact dates, or find your zone by ZIP if you are not sure which one you are in.

Radishes are the fastest fall insurance crop. Fall roots stay milder and split less than spring ones because the soil is cooling rather than heating.

Fall dates are counted backward from your first frost, not forward from a sowing date. Take the 28 days radishes needs, add about two weeks because growth slows once days shorten after the equinox, then subtract the roughly 21 days radishes keeps going once light frost arrives. That is 21 days before your first frost. The coldest zone where this still works on the averages is Zone 3a.

For the whole-garden version of this arithmetic, see the fall planting calendar by zone, and how to read and stretch your first frost date.

Radishes grow well next to carrots, cucumbers, squash (winter) and spinach. Germinates in days rather than weeks, marking a slow row and pulling flea beetles and cucumber beetles off slower neighbors. The full grid for all 24 crops is in the companion planting chart.