When to Plant Tomatoes in Colorado
America's favorite garden vegetable (technically a fruit). Nothing beats a sun-warmed tomato straight off the vine.
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 |
Tomatoes 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 Tomatoes in Colorado
Tomatoes in Colorado's Climate
In cold climates with 120-160 frost-free days, tomatoes demand an aggressive indoor start 6-8 weeks before your last frost. Choose short-season varieties that mature in 55-65 days — Stupice, Sub Arctic Plenty, and Glacier are bred for regions exactly like yours. Black plastic mulch can raise soil temperature by 10-15°F, and floating row cover over transplants during cool June nights adds critical warmth. Your goal is getting ripe tomatoes before September frost — every warm day counts.
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. Make sure soil has warmed to at least 60°F before planting tomatoes outside.
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. Tomatoes cannot tolerate any frost, so wait until all frost danger has passed before transplanting outside. Watch local forecasts carefully in spring.
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 tomatoes — transplant timing shifts by several weeks across the state.
Growing Tips
Pinch off suckers for indeterminate varieties. Stake or cage for best results. Water at the base, not overhead, to prevent blight.
Companion Planting
Plant tomatoes alongside these companions for better growth:
Keep tomatoes away from:
The Bottom Line
Last reviewed: March 29, 2026