Frost Dates for Johnstown, CO 80534
Last spring frost May 4 · First fall frost October 1 · 150 frost-free days · USDA Zone 5b
ZIP 80534 has about 20,500 people.
Moderate season: 150 frost-free days. Spring frost risk spans April 22–May 15 (23 days). Fall frost risk spans September 17–October 14 (27 days).
Frost probability for 80534
| Frost | 10% | 50% | 90% |
|---|---|---|---|
| Spring (last frost) | May 15 | May 4 | April 22 |
| Fall (first frost) | September 17 | October 1 | October 14 |
Dates come from NOAA 1971–2000 freeze probabilities at FT COLLINS (30.0 km away); the 50% date is the median year.
Which crops fit a 150-day season in Johnstown
In Johnstown (150 frost-free days, a moderate season), 34 of 56 planner crops fit outright, 21 get two plantings, 1 crop is perennial.
| Crop | Start indoors | Plant out / sow | Days you have | Verdict | Last sow date |
|---|---|---|---|---|---|
| Tomato | Mar 30 | May 18–May 25 | 108 | fits: 80 days to maturity, 108 available after May 18. | Jun 1 |
| Pepper | Mar 23 | May 18–May 25 | 108 | fits: 75 days to maturity, 108 available after May 18. | Jun 6 |
| Lettuce | Mar 9 | Apr 6–Apr 13 | 185 | two-plantings: Plant Apr 6 and again by Aug 10; both mature before Oct 8. | Aug 10 |
| Carrots | — | Apr 13–Apr 20 | 192 | fits: 70 days to maturity, 192 available after Apr 13. | Jul 30 |
| Cucumber | Apr 13 | May 18–May 25 | 122 | fits: 60 days to maturity, 122 available after May 18. | Jul 5 |
| Beans | — | May 11–May 25 | 136 | two-plantings: Plant May 11 and again by Jul 12; both mature before Sep 24. | Jul 12 |
| Peas | — | Mar 9–May 18 | 213 | fits: 65 days to maturity, 213 available after Mar 9. | Jul 21 |
| Zucchini | Apr 20 | May 18–May 25 | 122 | fits: 55 days to maturity, 122 available after May 18. | Jul 10 |
| Onion | Feb 9 | Apr 6–Apr 20 | 185 | fits: 100 days to maturity, 185 available after Apr 6. | — |
| Spinach | — | Mar 9–Apr 27 | 227 | two-plantings: Plant Mar 9 and again by Aug 29; both mature before Oct 22. | Aug 29 |
| Kale | Feb 23 | Apr 6–Apr 20 | 199 | two-plantings: Plant Apr 6 and again by Aug 14; both mature before Oct 22. | Aug 14 |
| Broccoli | Mar 9 | Apr 6–Apr 20 | 185 | fits: 80 days to maturity, 185 available after Apr 6. | Jul 6 |
| Cabbage | Mar 9 | Apr 6–Apr 20 | 199 | fits: 70 days to maturity, 199 available after Apr 6. | Jul 30 |
| Radish | — | Mar 9–Jun 1 | 213 | two-plantings: Plant Mar 9 and again by Aug 30; both mature before Oct 8. | Aug 30 |
| Beets | — | Mar 9–Jun 1 | 213 | two-plantings: Plant Mar 9 and again by Jul 31; both mature before Oct 8. | Jul 31 |
| Potatoes | — | Apr 20–Apr 27 | 171 | fits: 90 days to maturity, 171 available after Apr 20. | — |
| Garlic | — | Oct 1 | 255 | overwinter: Plant Oct 1 to Oct 22; harvest the following summer. | Oct 22 |
| Strawberry | — | Mar 30–May 25 | 206 | perennial: A perennial: plant Mar 30; it fruits from the following year and keeps producing for several years. | — |
| Corn | Apr 6 | May 11–May 18 | 122 | fits: 75 days to maturity, 122 available after May 11. | Jun 13 |
| Pumpkin | Apr 20 | May 18–May 18 | 115 | fits: 100 days to maturity, 115 available after May 18. | May 19 |
| Cauliflower | Mar 23 | Apr 27–May 11 | 164 | fits: 75 days to maturity, 164 available after Apr 27. | Jul 11 |
| Swiss Chard | Mar 9 | Apr 20–Apr 20 | 171 | two-plantings: Plant Apr 20 and again by Jul 31; both mature before Oct 8. | Jul 31 |
| Arugula | — | Mar 9–Jun 1 | 227 | two-plantings: Plant Mar 9 and again by Aug 29; both mature before Oct 22. | Aug 29 |
| Brussel Sprouts | Mar 9 | Apr 6–Apr 20 | 199 | fits: 100 days to maturity, 199 available after Apr 6. | Jun 30 |
| Butternut Squash | Apr 20 | May 18–May 25 | 115 | fits: 100 days to maturity, 115 available after May 18. | May 19 |
| Eggplant | Mar 16 | May 18–May 25 | 108 | fits: 70 days to maturity, 108 available after May 18. | Jun 11 |
| Okra | Apr 6 | May 11–May 18 | 129 | two-plantings: Plant May 11 and again by Jul 10; both mature before Sep 17. | Jul 10 |
| Basil | Mar 30 | May 25–May 25 | 115 | fits: 60 days to maturity, 115 available after May 25. | Jul 5 |
| Cilantro | — | Apr 6–Apr 27 | 185 | two-plantings: Plant Apr 6 and again by Aug 5; both mature before Oct 8. | Aug 5 |
| Parsley | Feb 23 | May 11–May 18 | 150 | fits: 70 days to maturity, 150 available after May 11. | Jul 16 |
| Celery | Feb 23 | May 11–May 25 | 150 | fits: 120 days to maturity, 150 available after May 11. | May 27 |
| Scallions | Feb 23 | Apr 6–Apr 20 | 199 | two-plantings: Plant Apr 6 and again by Aug 9; both mature before Oct 22. | Aug 9 |
| Turnip | — | Apr 6–Apr 20 | 199 | two-plantings: Plant Apr 6 and again by Aug 19; both mature before Oct 22. | Aug 19 |
| Kohlrabi | — | Mar 23–Apr 6 | 213 | two-plantings: Plant Mar 23 and again by Aug 14; both mature before Oct 22. | Aug 14 |
| Bok Choy | Apr 6 | Apr 27–May 4 | 164 | two-plantings: Plant Apr 27 and again by Aug 10; both mature before Oct 8. | Aug 10 |
| Collards | Feb 23 | Apr 6–Apr 20 | 199 | two-plantings: Plant Apr 6 and again by Aug 9; both mature before Oct 22. | Aug 9 |
| Cantaloupe | Apr 20 | May 18–May 25 | 108 | fits: 85 days to maturity, 108 available after May 18. | May 27 |
| Chives | Feb 9 | May 11–May 18 | 164 | fits: 90 days to maturity, 164 available after May 11. | — |
| Dill | — | Mar 9–Jun 1 | 213 | two-plantings: Plant Mar 9 and again by Jul 31; both mature before Oct 8. | Jul 31 |
| Oregano | Feb 23 | May 11–May 18 | 164 | fits: 80 days to maturity, 164 available after May 11. | — |
| Rosemary | Feb 9 | May 11–May 18 | 150 | fits: 80 days to maturity, 150 available after May 11. | — |
| Sage | Mar 9 | May 11–May 18 | 164 | fits: 75 days to maturity, 164 available after May 11. | — |
| Thyme | Feb 23 | May 11–May 18 | 164 | fits: 90 days to maturity, 164 available after May 11. | — |
| Calendula | Mar 23 | Apr 20–May 4 | 171 | two-plantings: Plant Apr 20 and again by Aug 5; both mature before Oct 8. | Aug 5 |
| Cosmos | Apr 6 | May 4–May 18 | 136 | two-plantings: Plant May 4 and again by Jul 5; both mature before Sep 17. | Jul 5 |
| Lavender | Feb 9 | May 4–May 18 | 171 | fits: 90 days to maturity, 171 available after May 4. | — |
| Marigolds | Mar 23 | May 4–May 11 | 136 | two-plantings: Plant May 4 and again by Jul 15; both mature before Sep 17. | Jul 15 |
| Melons | Apr 20 | May 18–May 25 | 108 | fits: 85 days to maturity, 108 available after May 18. | May 27 |
| Mint | — | May 4–May 18 | 171 | fits: 90 days to maturity, 171 available after May 4. | — |
| Nasturtiums | Apr 6 | May 4–May 11 | 136 | two-plantings: Plant May 4 and again by Jul 10; both mature before Sep 17. | Jul 10 |
| Pole Beans | — | May 11–May 25 | 129 | fits: 65 days to maturity, 129 available after May 11. | Jun 30 |
| Spaghetti Squash | Apr 20 | May 18–May 25 | 115 | fits: 90 days to maturity, 115 available after May 18. | May 29 |
| Sunflowers | — | May 4–May 18 | 136 | fits: 70 days to maturity, 136 available after May 4. | Jun 25 |
| Tomatillos | Mar 9 | May 11–May 18 | 115 | fits: 75 days to maturity, 115 available after May 11. | Jun 6 |
| Watermelon | Apr 20 | May 11–May 18 | 115 | fits: 80 days to maturity, 115 available after May 11. | Jun 1 |
| Yellow Squash | Apr 20 | May 18–May 25 | 122 | fits: 55 days to maturity, 122 available after May 18. | Jul 10 |
| Zinnias | Apr 6 | May 4–May 18 | 136 | two-plantings: Plant May 4 and again by Jul 5; both mature before Sep 17. | Jul 5 |
Month by month in Johnstown
| Month | What to do |
|---|---|
| January | Plan your garden layout and order seeds. Research varieties suited to your frost dates. |
| February | Start indoors: Chives (Feb 9), Lavender (Feb 9), Onion (Feb 9), Rosemary (Feb 9), Celery (Feb 23), Collards (Feb 23), +5 more. |
| March | Start indoors: Broccoli (Mar 9), Brussel Sprouts (Mar 9), Cabbage (Mar 9), Lettuce (Mar 9), Sage (Mar 9), Swiss Chard (Mar 9), +8 more. Direct sow from: Arugula (Mar 9), Beets (Mar 9), Dill (Mar 9), Peas (Mar 9), Radish (Mar 9), Spinach (Mar 9), +1 more. Plant: Strawberry (Mar 30). |
| April | Start indoors: Bok Choy (Apr 6), Corn (Apr 6), Cosmos (Apr 6), Nasturtiums (Apr 6), Okra (Apr 6), Zinnias (Apr 6), +9 more. Direct sow from: Cilantro (Apr 6), Turnip (Apr 6), Carrots (Apr 13), Potatoes (Apr 20). Transplant from: Broccoli (Apr 6), Brussel Sprouts (Apr 6), Cabbage (Apr 6), Collards (Apr 6), Kale (Apr 6), Lettuce (Apr 6), +6 more. |
| May | Direct sow from: Sunflowers (May 4), Beans (May 11), Pole Beans (May 11). Transplant from: Cosmos (May 4), Lavender (May 4), Marigolds (May 4), Mint (May 4), Nasturtiums (May 4), Zinnias (May 4), +23 more. Last frost around May 4. Last sowing dates: Butternut Squash (May 19), Pumpkin (May 19), Cantaloupe (May 27), Celery (May 27), Melons (May 27), Spaghetti Squash (May 29). |
| June | Last sowing dates: Tomato (Jun 1), Watermelon (Jun 1), Pepper (Jun 6), Tomatillos (Jun 6), Eggplant (Jun 11), Corn (Jun 13), +3 more. |
| July | Last sowing dates: Basil (Jul 5), Cosmos (Jul 5), Cucumber (Jul 5), Zinnias (Jul 5), Broccoli (Jul 6), Nasturtiums (Jul 10), +13 more. |
| August | Last sowing dates: Calendula (Aug 5), Cilantro (Aug 5), Collards (Aug 9), Scallions (Aug 9), Bok Choy (Aug 10), Lettuce (Aug 10), +6 more. |
| September | First fall frost approaching (around October 1). Transplant fall brassicas. Sow spinach, arugula, and radishes. |
| October | Direct sow from: Garlic (Oct 1). First frost around October 1. Last sowing dates: Garlic (Oct 22). |
| November | Harvest remaining cold-hardy crops: kale, carrots, and beets. Plant garlic bulbs for next year. |
| December | Clean up spent plants. Add compost to beds. Rest, review, and plan next year's garden. |
Frequently Asked Questions
What is the last frost date for Johnstown, CO (ZIP 80534)?
The median last spring frost date for Johnstown, CO (ZIP code 80534) is around May 4. This is the 50th-percentile date — meaning half of all years see frost end before this date. Use the 10% and 90% dates to understand the full range of risk in your area. One year in ten frost ends before April 22; one in ten it runs past May 15.
What is the first fall frost date in Johnstown, CO?
The median first fall frost date for Johnstown, CO is around October 1. Plan to harvest or protect frost-sensitive crops like tomatoes and peppers at least a week before this date to avoid losses. The first frost arrives around September 17 in the earliest one-in-ten years, so cover tomatoes and peppers from then.
How long is the growing season in Johnstown, CO?
The frost-free growing season in Johnstown is about 150 days. This window — from your last spring frost to your first fall frost — is when warm-season vegetables thrive. Cold-hardy crops like kale, spinach, and peas can extend your season by weeks on either side. In Johnstown (150 frost-free days, a moderate season), 34 of 56 planner crops fit outright, 21 get two plantings, 1 crop is perennial.
What USDA hardiness zone is Johnstown, CO?
Johnstown, CO is in USDA hardiness zone 5b (2023 USDA Plant Hardiness Zone Map). Zones come from the average coldest winter temperature, so they tell you which perennials survive the winter; the frost dates on this page tell you when to plant.
When should I start tomatoes indoors in Johnstown, CO?
Start tomatoes indoors Mar 30 and plant out May 18 in Johnstown. The planner uses the local median last frost and this crop's indoor-start and transplant offsets.
How many plantings of lettuce fit in Johnstown?
Two: plant Apr 6 and again by Aug 10; both mature before Oct 8.
When do I plant garlic in Johnstown?
Oct 1 to Oct 22; it overwinters and is ready the following summer.
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