When to Plant in Denver, CO: Planting Calendar & Frost Dates

For ZIP 80202 in Denver, the nearest NOAA weather station with freeze records is Denver Water Department (NOAA name: Denver Water Dept, CO), 1.6 miles away. Its median last spring frost (32°F, NOAA 1991–2020) is Apr 30 and its median first fall frost is Oct 12, leaving about 165 frost-free days. ZIP 80202 is in USDA hardiness zone 6a. The last frost here comes 4 days later than the zone 6 median (Apr 26), and the season is 11 days shorter than the zone’s typical 176 days. Across Colorado’s 527 ZIP codes with frost dates, the median last frost is May 9, so Denver’s comes 9 days earlier than that.

Station and dates: NOAA NCEI U.S. Climate Normals 1991–2020, 32°F at 50% probability, for the station nearest the center of ZIP 80202. Zone: 2023 USDA Plant Hardiness Zone Map (PRISM data by ZIP code). Outside Delaware, Maryland, Pennsylvania, New Jersey and Virginia the planner uses the nearest NOAA station with freeze data, which can be at a different elevation from your yard.

Key planting dates for Denver

Denver vegetable and flower planting calendar

Every date range below is counted from Denver’s median frost dates (Apr 30 and Oct 12) with the same rules as our planner, and rows run in calendar order. In about half of years a frost still comes after the spring date.

How we count planting dates: the weeks before or after frost for each crop come from university extension planting guides: UNH Extension, When to Plant Your Vegetable Garden; Rutgers FS787, Starting Vegetable Seeds Indoors; Virginia Tech 426-331, Home Garden Vegetable Planting Guide; University of Maryland Extension, Vegetable Planting Calendar; and University of Idaho CIS 1209 (marigolds and zinnias). Bulb windows approximate Rutgers’ rule to plant when soil falls below 60°F (FS1220), and garlic follows SDSU, Illinois and Virginia Tech. Temperature notes: UMD (potatoes), UMN (sweet corn), UC ANR (peppers, hardening off), UMN (eggplant), Colorado State (tomatoes) and SDSU (hardening off).

Harvest estimates add days to harvest from these sources to each planting window, and stop at the first fall frost for frost-tender crops: UF/IFAS Extension, Florida Vegetable Gardening Guide (SP103/VH021), Table 1, “Days to Harvest”; University of Maryland Extension, Growing Onions in a Home Garden; University of Maryland Extension, Growing Garlic in a Home Garden; University of Maryland Extension, Growing Basil in a Home Garden.

Frost dates across Denver’s ZIP codes

Across Denver’s 31 ZIP codes, the median last spring frost ranges from Apr 30 to May 7 and the median first fall frost from Oct 8 to Oct 12, depending on which of 5 NOAA stations is nearest. This page uses ZIP 80202, which is in the group most Denver ZIP codes share.

Which ZIP codes count as Denver: the 31 ZIP Code Tabulation Areas (2020 ZCTAs) with at least half of their land area inside Denver city limits, from the U.S. Census Bureau, 2020 ZCTA to Place Relationship File. ZCTAs are the Census Bureau’s approximations of USPS ZIP Code areas, so this list may not match every USPS ZIP code. Each ZIP code’s dates are the ones our planner shows for it.

How Denver compares

How this table is built: each ZIP code is matched to its nearest NOAA 1991–2020 freeze-data station (within 60 miles); state and zone rows are medians across those ZIP codes. Zones are the 2023 USDA zones by ZIP code (PRISM).

More for Denver gardeners

• Your own ZIP: open the planner for ZIP 80202 and change the ZIP to yours for its own station and dates.
• Colorado: When to plant in Colorado, with frost dates across the state.
• USDA zone 6a: our zone 6 planting guide.
• Frost tonight? How to protect plants from frost.

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