Colorado Front Range planting calendar
On Colorado's Front Range (USDA zones 5–6), plant cool-season vegetables 2–4 weeks before the average last frost (early-to-mid May), set out warm-season crops once soil reaches 60 °F (usually late May), plant trees, shrubs, and fall bulbs in September–October, and deep-water established plants about monthly through winter. Here's the month-by-month guide.
What to plant when
Cool-season vegetables (peas, spinach, lettuce, kale)
Direct-sow / transplant 2–4 weeks before your average last frost — typically late March–April.
These hardy crops tolerate light frost and bolt in summer heat, so get them in early; a second sowing in late summer gives a fall harvest. (CSU GardenNotes #720)
Warm-season crops (tomatoes, peppers, squash, basil)
After your last frost AND once soil reaches 60 °F (55 °F minimum) — usually mid-to-late May.
Soil temperature matters more than the calendar: transplants set into cold soil stall. Start seeds indoors ~6–8 weeks before last frost and harden off before transplanting. (CSU GardenNotes #717)
Trees & shrubs
Spring or — best for the Front Range — early fall (September–October).
Fall planting lets roots establish in still-warm soil before winter; water new woody plants through their first winters. Divide perennials in September too. (PlantTalk: Trees, Shrubs & Vines)
Fall bulbs (tulips, daffodils, crocus)
Plant September–October, before the ground freezes.
Spring-blooming bulbs need cold-soil weeks to root; plant early in the window for best establishment, up until late October. (PlantTalk #1086)
Winter watering
About 1–2× per month, October–April — only when air is above 40 °F, soil is unfrozen, and there's no snow cover; water at midday so it soaks in before night.
Front Range winters are dry and sunny; unwatered roots desiccate. Apply to trees, shrubs, lawns, and perennials, and always follow your utility's current drought restrictions. (CSU Extension 7.211)
Average frost dates by city
Frost dates are averages — local elevation and microclimate shift them, so treat them as windows, not guarantees. Tap a city for its full local guide.
| City | Avg. last spring frost | Avg. first fall frost | Growing season |
|---|---|---|---|
| Boulder | ~May 5 | early October | 144 days |
| Colorado Springs | mid-May | ~October 5 | 145 days |
| Castle Rock | mid-to-late May (cold-air pooling can push frost later at elevation — verify locally) | mid-to-late September | 130 days |
| Fort Collins | ~May 11 | early-to-mid October | 146 days |
| Denver | mid-May | early-to-mid October | 150 days |
| Aurora | mid-May | early-to-mid October | 150 days |
| Longmont | late April–mid May | late September–mid October | 150 days |
| Loveland | early-to-mid May | early-to-mid October | 145 days |
| Greeley | ~May 4 | ~October 4 | 150 days |
Front Range planting FAQ
- When can I plant tomatoes on the Colorado Front Range?
- After your area's last frost and once the soil reaches about 60 °F (55 °F minimum) — usually mid-to-late May. Soil temperature matters more than the date; transplants set into cold soil stall.
- When do I plant tulips and other fall bulbs in Colorado?
- September–October, before the ground freezes — plant early in that window for the best root establishment.
- When is the last frost on the Front Range?
- Roughly early-to-mid May for most Front Range cities, but it varies — Greeley averages ~May 4 while higher Castle Rock can see frost into early June. See the by-city table above.
- Can I plant anything before the last frost?
- Yes — cool-season vegetables (peas, spinach, lettuce, kale) and many trees, shrubs, and perennials go in weeks before the last frost. Only frost-tender, warm-season plants need to wait.
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