When to Plant in Denver, CO

Denver sits at 5,280 feet elevation — Zone 6a with a typical last frost around May 9. The mile-high altitude means intense UV rays, cool nights even in summer, and a risk of late frosts well into May. Afternoon thunderstorms and occasional hail are summer hazards.

Denver gardeners work with a growing season of roughly 150–160 days. Starting seeds indoors is essential for tomatoes and peppers, and choosing short-season varieties helps ensure harvest before the first fall frost around October 1.

What to plant now in Denver

Spring: Cool-season crops in April; tomatoes and peppers after May 9 last frost.
Summer: Full warm-season garden. Water consistently — limited summer rain.
Fall: Broccoli, kale, lettuce, spinach, and carrots for September–October harvest.
Winter: Garlic planted in October overwinters. Planning and seed starting.

In Denver (145 frost-free days, a moderate season), 37 of 56 planner crops fit outright, 18 get two plantings, 1 crop is perennial.

Month by month in Denver

Month	What to do
January	Order seeds. Plan garden layout. Research short-season varieties.
February	Start onion seeds indoors. Begin planning seed starting schedule.
March	Start tomato and pepper seeds indoors (8–10 weeks before May 9 last frost).
April	Direct sow peas, spinach, and lettuce outdoors. Start squash seeds indoors.
May	After May 9 — transplant all warm-season crops. Watch for late frost.
June	Full summer garden. Watch for hail — keep hail cloth handy.
July	Harvest summer crops. Water consistently. Start fall seedlings.
August	Plant fall broccoli, kale, and lettuce transplants. Direct sow carrots.
September	Fall crops growing fast. First frost possible late September.
October	First frost around October 1. Harvest or protect tender crops. Plant garlic.
November	Garden winds down. Mulch garlic beds.
December	Rest season. Plan next year.

Frost dates for Denver ZIP codes

ZIP	Last spring frost (50%)	First fall frost (50%)	Zone
80219	May 9	October 1	6a
80233	May 9	October 1	6a
80249	May 9	October 1	6a
80221	May 9	October 1	6a
80210	May 9	October 1	6a
80260	May 4	October 2	6a
80205	May 9	October 1	6a
80214	May 9	October 1	6a
80206	May 9	October 1	6a
80222	May 9	October 1	6a
80224	May 9	October 1	6a
80223	May 9	October 1	6a
80218	May 9	October 1	6a
80264	May 9	October 1	5b (est.)

FAQ

When is the last frost date in Denver, CO?

Denver's average last frost date is around May 9. Start tomato and pepper seeds indoors in mid-March and don't transplant outdoors until after early May.

How does Denver's altitude affect gardening?

The 5,280-foot elevation means intense UV rays that can scorch plants, cool nights that slow warm-season crops, and lower atmospheric pressure that changes water needs. Use sunscreen on new transplants!

What about hail in Denver?

Denver's summer thunderstorms can bring damaging hail. Hail cloth or shade cloth provides protection. Keep old sheets or row covers handy to throw over plants quickly when storms approach.

What grows best in Denver?

Short-season tomatoes, peppers, squash, and beans do well in summer. Fall is excellent for kale, lettuce, broccoli, and carrots. Potatoes and root vegetables thrive in Denver's cool soil.

How does Plan My Garden help Denver gardeners?

Enter your Denver zip code and we'll generate planting dates calibrated to the Front Range's altitude, frost dates, and short growing season.