When to Plant Radishes in Colorado
Published: April 24, 2026
Colorado gardeners in Zone 6a have a 31-week growing season for radish (March 30 to November 1). Colorado's spring and fall windows both work well for radish — some gardeners plant both successions for a long harvest. This guide gives exact dates for Colorado based on your local frost calendar.
Radish Planting Dates for Colorado
| Start seeds indoors | Year-round |
| Last frost (average) | March 30 |
| Direct sow outdoors | February 23–March 5 |
| Expect first harvest | March 17 – March 25 |
| Fall crop start | September 27–October 7 |
| Fall harvest | October 19 |
| First fall frost (average) | November 1 |
Dates above assume Zone 6a, the most common zone in Colorado. Gardeners in cooler Denver (Zone 6a) plant 1–2 weeks later; warmer Colorado Springs (Zone 6b) can plant 1–2 weeks earlier.
⚠ Direct sow radishes 4–6 weeks before last frost — one of the fastest crops in the garden. Ready in as little as 22 days. Succession plant every 2 weeks for continuous harvest.
Growing Radishes in Colorado's Climate
Colorado's moderate Zone 6a climate is well-suited to radish with minimal special accommodation. The standard transplant calendar works as written, and harvest windows line up with what seed packets recommend without adjustment.
Succession planting extends your radish harvest significantly in Colorado. A second planting 3 to 4 weeks after the first gives you a backup in case of pest pressure and extends the total harvest window into early fall.
Common radish pests to watch for in Colorado include Flea Beetle and Cabbage Root Maggot. The first line of defense is companion planting: Lettuce and Carrot planted nearby discourage several of these pests by confusing host-plant identification or repelling adults before they can lay eggs. Weekly garden walks in the early morning catch problems when they're still manageable.
Radish Garden Calendar for Colorado
| Month | Task | Notes |
|---|---|---|
| January | — | Dormant season |
| February | Direct sow seeds | Sow seeds 1/4–1/2 inch deep, 2 inches apart |
| March | First harvest window opens | Radish begins producing 22–30 days after transplant |
| April | — | Dormant season |
| May ← | Watch for bolting | Harvest promptly; spring heat arrives quickly |
| June | — | Dormant season |
| July | — | Dormant season |
| August | — | Dormant season |
| September | Fall crop planting | Transplant or direct sow for fall harvest before frost |
| October | — | Dormant season |
| November | First frost approaches | Harvest remaining radish; cover plants on frost nights |
| December | — | Dormant season |
Radish Growing Tips for Colorado Gardeners
- •Thin to 2-inch spacing when seedlings are an inch tall — crowded radishes produce small woody roots.
- •Succession plant every 10–14 days from early spring through late spring for continuous harvest.
- •Colorado's moderate climate supports succession planting — sow new transplants or seeds every 3 weeks during spring to extend the harvest window into fall.
- •Plant as a row marker for slow-germinating crops like carrots — radishes sprout in days and mark the rows.
Companion Planting for Radishes in Colorado
In Colorado's moderate climate, planting radish with Lettuce and Carrot helps deter pests and improve soil. Avoid planting near Hyssop and Grape, which inhibit radish growth through root chemistry or shared pest pressure. See the full radish companion planting guide for the complete list.
Radishes Planting Dates by City in Colorado
Top cities in Colorado — select for city-level frost dates and planting calendars.
Frequently Asked Questions
When should I plant radish in Colorado?
In Colorado (Zone 6a), start radish seeds indoors around Year-round and transplant outdoors around null — 0 weeks after the state's average last frost of March 30.
What is the last frost date in Colorado?
Colorado's average last frost date is March 30 in the state's most common Zone 6a. Frost dates vary by city — higher elevations and northern counties run 1 to 3 weeks later than the state average. See the city list below for city-level frost dates.
Can I grow radish year-round in Colorado?
radish is a cool-season crop in Colorado, with spring and fall windows. Summer heat bolts the plants before they can produce a harvestable crop. Succession planting every 2–3 weeks stretches the harvest window.
What radish varieties grow best in Colorado?
For Colorado's Zone 6a, consult a local nursery or extension office for radishes variety recommendations.
When do I start radish seeds indoors in Colorado?
Radish does not need indoor starting in Colorado — direct sow around February 23–March 5 once soil reaches 40°F. Indoor starting is not recommended for this crop because radish transplants poorly.