Longmont, CO — USDA Zone 5b

Frost dates and growing season in Longmont

All of Longmont's mapped ZIP codes fall in the same hardiness band, Zone 5b.

These are 50%-probability averages modeled from Longmont's USDA hardiness zone and regional climate normals — not a single-station reading. In a typical year the last spring frost will have passed by May 9, but a colder-than-average year can run 1-2 weeks later. Plant tender crops (tomatoes, peppers, basil) once both soil and night temperatures are consistently warm — a thermometer beats the calendar.

Growing season in Longmont

Longmont, Colorado sits in USDA Zone 5b, with roughly 144 frost-free days between an average last spring frost around May 9 and a first fall frost around September 30. That is a standard temperate season — most common vegetables finish comfortably, and a single main planting plus one succession round works well.

What grows in Longmont

Longmont falls in USDA Zone 5b, so the same hardiness constraints apply as the full Zone 5 guide. Vegetables, herbs, and fruit trees rated to Zone 5b (or hardier) will overwinter here in a typical year.

• Tomatoes (full range of varieties)
• Peppers
• Eggplant
• Squash, melons, cucumbers
• Beans (bush + pole)
• Sweet corn
• Apples, pears, plums
• Cherries (sweet + sour)
• Blueberries, raspberries
• Garlic

What to plant in Longmont this week

Longmont's first fall frost typically arrives September 30. Fall-planted crops go in now — garlic, brassicas, and cool-season greens will run through winter.

• When to plant garlic in zone 5
• When to plant lettuce in zone 5
• When to plant carrots in zone 5
• When to plant peas in zone 5

Full planting calendar for Longmont

Crop-by-crop sowing, transplant, and harvest dates calibrated to zone 5 averages:

• When to plant tomatoes in zone 5
• When to plant peppers in zone 5
• When to plant basil in zone 5
• When to plant garlic in zone 5
• When to plant lettuce in zone 5
• When to plant bush beans in zone 5
• When to plant cucumbers in zone 5
• When to plant summer squash in zone 5
• When to plant peas in zone 5
• When to plant carrots in zone 5
• When to plant broccoli in zone 5
• When to plant cauliflower in zone 5
• When to plant cabbage in zone 5
• When to plant kale in zone 5
• When to plant brussels sprouts in zone 5
• When to plant collard greens in zone 5
• When to plant spinach in zone 5
• When to plant swiss chard in zone 5
• When to plant arugula in zone 5
• When to plant beets in zone 5
• When to plant radishes in zone 5
• When to plant turnips in zone 5
• When to plant parsnips in zone 5
• When to plant kohlrabi in zone 5
• When to plant onions in zone 5
• When to plant leeks in zone 5
• When to plant celery in zone 5
• When to plant asparagus in zone 5
• When to plant rhubarb in zone 5
• When to plant potatoes in zone 5
• When to plant sweet potatoes in zone 5
• When to plant eggplant in zone 5
• When to plant okra in zone 5
• When to plant sweet corn in zone 5
• When to plant pumpkins in zone 5
• When to plant winter squash in zone 5
• When to plant zucchini in zone 5
• When to plant cantaloupe in zone 5
• When to plant watermelon in zone 5
• When to plant pole beans in zone 5
• When to plant edamame in zone 5
• When to plant fava beans in zone 5
• When to plant cilantro in zone 5
• When to plant dill in zone 5
• When to plant parsley in zone 5
• When to plant oregano in zone 5
• When to plant thyme in zone 5
• When to plant sage in zone 5
• When to plant chives in zone 5

ZIP codes in Longmont

Drill down to the precise frost window and planting calendar for a specific ZIP in Longmont:

• 80501 — Longmont (Zone 5b)

Local microclimate notes

Zone tables give you the average — but Longmont gardens vary. South-facing walls and paved areas can run a full half-zone warmer than the published rating. Low-lying spots, frost pockets, and shaded north sides can run colder. If you've gardened here a few seasons, your own frost record — the last time you actually got frost damage — beats any national average.

Source and methodology

Hardiness zone from the USDA Plant Hardiness Zone Map (2023 revision). Frost-date and growing-season figures are modeled from Longmont's USDA hardiness zone and regional NOAA 1991-2020 climate normals — zone-level estimates, not a per-station record, so treat them as planning guidance and confirm against your own local frost history. Crop recommendations draw on US Cooperative Extension references, curated by the Growli editorial team. Last reviewed June 2026.

Other cities in Colorado

• Arvada, CO — USDA Zone 6a
• Aurora, CO — USDA Zone 6a
• Boulder, CO — USDA Zone 6a
• Colorado Springs, CO — USDA Zone 6a
• Denver, CO — USDA Zone 6a
• Fort Collins, CO — USDA Zone 5b
• Glenwood Springs, CO — USDA Zone 6a
• Grand Junction, CO — USDA Zone 7a
• Greeley, CO — USDA Zone 5b
• Highlands Ranch, CO — USDA Zone 5b
• Lakewood, CO — USDA Zone 6a
• Littleton, CO — USDA Zone 6a
• All of Colorado by zone

Related guides

• USDA Zone 5 — full plant + frost guide
• Browse USDA hardiness zones by city
• Look up a ZIP code
• How to start a vegetable garden — beginner guide