🌶️When to Plant Radish in USDA Zone 4a (2026 Guide)
The fastest crop in the garden. Ready in under a month. Here is the cool-season planting schedule for radish in zone 4a (covering areas like northern Wisconsin, Fargo ND). All dates are based on 2026 frost data for your zone.
Direct sow
Apr 12
Harvest From
May 10
Because radish is a cool-season crop, it tolerates light frost and can go out around Apr 12, before zone 4a's average last frost on May 10.
- Type: Cool-season
- Method: Direct sow
- Days to harvest: 28
- Spacing: 2" apart
- Sun: Full sun to part shade
- Zone 4a frost: May 10 – Sep 25
- Season length: ~138 days
- Companions: carrot, lettuce, spinach
Growing radish in zone 4a
Zone 4a has an average last spring frost around May 10 and a first fall frost around Sep 25, giving roughly 138 frost-free growing days. That window comfortably fits radish's 28-day cycle, with room for a second succession planting if you time it right.
Radish resents transplanting, so direct sow it right in the garden around Apr 12. Give each plant about 2 inches of space in full sun to part shade.
Zone 4a specific growing notes
In zone 4a (northern Wisconsin, Fargo ND), your 138-day growing season means radish should be one of your first spring plantings. Cool-season crops thrive in the mild part of your growing window. Monitor soil temperature — radish germinates best when soil is 40-75°F.
Your first fall frost around Sep 25 means your last possible harvest is roughly late Sep. For a continuous supply, consider succession planting every 2-3 weeks from Apr 12 through mid-season.
Pro tip for radish
Sow thinly—overcrowding causes all leaves and no bulb formation. Thin to 2 inches apart ruthlessly. The thinnings are edible microgreens. For the mildest flavor, harvest promptly once shoulders push above soil.
Troubleshooting radish
Flea beetles chew tiny round holes (shotgun pattern) in leaves. While severe damage stunts root development, light damage is cosmetic. Row cover at sowing completely prevents infestation.
Growing radish in containers
Shallow 4-6 inch deep trays work perfectly—radishes are the easiest container vegetable. One 12-inch windowsill planter produces a fresh batch every month. Great for kids and beginners.
Can you plant radish twice a year?
Absolutely—sow every 2 weeks in spring and again when temperatures cool in late summer. Skip mid-summer (July) in hot zones—radishes bolt and turn woody above 80°F. Fall radishes are sweeter.
Frequently asked questions
When should I plant radish in zone 4a?
Direct sow around Apr 12. Because radish is a cool-season crop, it tolerates light frost and can go out around Apr 12, before zone 4a's average last frost on May 10.
How long does radish take to grow in zone 4a?
About 28 days from sowing to first harvest. A Apr 12 planting in zone 4a is typically ready to pick from around May 10. Zone 4a has about 138 frost-free days — plenty of time for a second succession planting.
How far apart should I space radish?
Space radish about 2 inches apart in full sun to part shade. This gives each plant enough room for roots to spread and leaves to catch sunlight without competing.
What is the best tip for growing radish?
Sow thinly—overcrowding causes all leaves and no bulb formation. Thin to 2 inches apart ruthlessly. The thinnings are edible microgreens. For the mildest flavor, harvest promptly once shoulders push above soil.
What are common problems with radish and how do I fix them?
Flea beetles chew tiny round holes (shotgun pattern) in leaves. While severe damage stunts root development, light damage is cosmetic. Row cover at sowing completely prevents infestation.
Can I grow radish in a container?
Shallow 4-6 inch deep trays work perfectly—radishes are the easiest container vegetable. One 12-inch windowsill planter produces a fresh batch every month. Great for kids and beginners.
Can I plant a second crop of radish for fall harvest?
Absolutely—sow every 2 weeks in spring and again when temperatures cool in late summer. Skip mid-summer (July) in hot zones—radishes bolt and turn woody above 80°F. Fall radishes are sweeter.
What grows well next to radish?
Good companion plants for radish are carrot, lettuce, spinach. Avoid planting near warm-season crops that compete for space and nutrients. Radish also benefits from crop rotation — do not plant it in the same spot year after year.