The “last frost” in Colorado depends a lot on where you are and your elevation, but for most Front Range cities it usually lands in mid‑May.

Quick Scoop: Typical last frost timing

Here’s a rough guide to average last frost dates across populated parts of Colorado (spring low near 32°F):

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Area / Example cities Typical last frost window Notes
Denver, Aurora, Arvada, Boulder, Fort Collins May 11–20 Front Range urban corridor at ~5,000–5,400 ft usually sees last freezes in mid‑May.
Colorado Springs, Highlands Ranch, Lakewood, Greeley May 11–20 Very similar to Denver, with garden calendars often using mid‑May as the “average last frost.”
Castle Rock, Golden, Durango, Ken Caryl May 21–31 Higher or more exposed locations tend to freeze a bit later into May.
Longmont, Erie, Pueblo, Fountain, Fort Carson May 1–10 Some lower‑elevation spots warm earlier, so the average last frost comes in early May.
Grand Junction, Clifton, Fruitvale April 21–30 Western Slope valley locations are among the earliest to lose frost risk.
High‑elevation areas (e.g., Black Forest and foothills) June 1–10 or later Some higher locations can freeze into June; gardeners there often treat June 10+ as the safer date.

Why it’s so variable in Colorado

Because of Colorado’s elevation and terrain, two gardens an hour apart can have different frost seasons. A Denver backyard might be safe to plant tomatoes by mid‑May, while a nearby foothills property still risks a hard freeze into June.

A common local “rule of thumb” is:

  • Along the I‑25 corridor (Denver to Fort Collins and Colorado Springs), plan for last frost around mid‑May.
  • In lower, warmer pockets (Pueblo, some western valleys), you can sometimes plant safely in late April or early May.
  • In higher elevations and mountain towns, assume risk into early to mid‑June.

How gardeners actually use these dates

Most Colorado gardeners treat the last frost date as an average, not a guarantee, and build in a buffer. A typical approach is:

  1. Start cool‑season crops (peas, spinach, lettuce) a few weeks before the average last frost.
  2. Wait until about 1–2 weeks after your local last frost window to plant tender crops like tomatoes, peppers, and basil.
  3. Keep frost cloth or sheets ready, because a surprise late cold snap can still happen even after the “average” last frost.

For example, a Denver gardener might use early May for hardy veggies, then wait until late May for tomatoes and peppers, just to be safe.

Bottom note: Information gathered from public forums or data available on the internet and portrayed here.