🌶️When to Plant Radish in USDA Zone 5b (2026 Guide)
The fastest crop in the garden. Ready in under a month. Here is the cool-season planting schedule for radish in zone 5b (covering areas like Denver CO, Columbus OH). All dates are based on 2026 frost data for your zone.
Direct sow
Mar 28
Harvest From
Apr 25
Because radish is a cool-season crop, it tolerates light frost and can go out around Mar 28, before zone 5b's average last frost on Apr 25.
- Type: Cool-season
- Method: Direct sow
- Days to harvest: 28
- Spacing: 2" apart
- Sun: Full sun to part shade
- Zone 5b frost: Apr 25 – Oct 10
- Season length: ~168 days
- Companions: carrot, lettuce, spinach
Growing radish in zone 5b
Zone 5b has an average last spring frost around Apr 25 and a first fall frost around Oct 10, giving roughly 168 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 Mar 28. Give each plant about 2 inches of space in full sun to part shade.
Zone 5b specific growing notes
In zone 5b (Denver CO, Columbus OH), your 168-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 Oct 10 means your last possible harvest is roughly late Oct. For a continuous supply, consider succession planting every 2-3 weeks from Mar 28 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 5b?
Direct sow around Mar 28. Because radish is a cool-season crop, it tolerates light frost and can go out around Mar 28, before zone 5b's average last frost on Apr 25.
How long does radish take to grow in zone 5b?
About 28 days from sowing to first harvest. A Mar 28 planting in zone 5b is typically ready to pick from around Apr 25. Zone 5b has about 168 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.