When to Plant Radishes in Colorado
The fastest vegetable in the garden — some varieties are ready in just 25 days. Perfect for impatient gardeners and kids.
The Short Answer
Colorado Frost Dates
Your planting dates depend on which part of Colorado you're in. Here are the frost date ranges by region:
| Region | Zones | Last Frost (Spring) | First Frost (Fall) |
|---|---|---|---|
| Front Range (Denver) | 5a, 5b, 6a | May 1 - May 15 | Sep 25 - Oct 10 |
| Western Slope | 4b, 5a, 5b, 6a | May 10 - Jun 1 | Sep 15 - Oct 5 |
| Mountain Regions | 3a, 3b, 4a, 4b | Jun 1 - Jun 20 | Aug 25 - Sep 15 |
Radishes Planting Schedule for Colorado
Front Range (Denver) (Zones 5a, 5b, 6a)
Average last frost: May 1 - May 15 · Average first frost: Sep 25 - Oct 10
Western Slope (Zones 4b, 5a, 5b, 6a)
Average last frost: May 10 - Jun 1 · Average first frost: Sep 15 - Oct 5
Mountain Regions (Zones 3a, 3b, 4a, 4b)
Average last frost: Jun 1 - Jun 20 · Average first frost: Aug 25 - Sep 15
Growing Radishes in Colorado
Radishes in Colorado's Climate
Radishes are perfect for cold-climate gardens — they're the fastest crop from seed to harvest (as few as 22 days) and tolerate frost. Direct sow as soon as soil thaws. Your cool, long spring means radishes grow for weeks without the bolting pressure that ends the season rapidly in warm zones. Fall radishes from an August sowing are equally productive.
Soil Considerations for Colorado
Alkaline clay soils common along Front Range. Rocky, thin soils in mountains. Amend heavily with compost and sulfur to lower pH. Loose, well-drained soil is especially important for radishes since the edible portion grows underground. If your soil is heavy clay, consider raised beds.
Colorado Climate & Growing Season
High altitude means intense sun but cool nights. Low humidity. Hail risk in late spring. Short but intense growing season at elevation. Radishes can handle frost well, which is an advantage in Colorado's climate. You can push planting dates earlier in spring and extend into fall.
Growing season length varies across Colorado: Front Range (Denver) (5a, 5b, 6a) has a last frost around May 1 - May 15, while Mountain Regions (3a, 3b, 4a, 4b) sees frost end around Jun 1 - Jun 20. This difference matters for radishes — but radishes handle frost well, so the timing difference is less critical.
Growing Tips
Don't let them stay in the ground too long — they get pithy and hot. Succession plant every 2 weeks for continuous harvest.
Companion Planting
Plant radishes alongside these companions for better growth:
The Bottom Line
Last reviewed: March 29, 2026