Frost Dates for Helena, MT 59601
Last spring frost June 6 · First fall frost September 12 · 98 frost-free days · USDA Zone 4b
ZIP 59601 has about 31,700 people, the largest of 4 ZIP codes in Helena.
Short season: 98 frost-free days. Spring frost risk spans May 21–June 21 (31 days). Fall frost risk spans August 31–September 23 (23 days).
Frost probability for 59601
| Frost | 10% | 50% | 90% |
|---|---|---|---|
| Spring (last frost) | June 21 | June 6 | May 21 |
| Fall (first frost) | August 31 | September 12 | September 23 |
Dates come from NOAA 1971–2000 freeze probabilities at AUSTIN 1 W (13.4 km away); the 50% date is the median year.
Frost dates by ZIP code in Helena, MT
| ZIP | Last spring frost (50%) | First fall frost (50%) | Zone |
|---|---|---|---|
| 59601 | June 6 | September 12 | 4b |
| 59602 | May 19 | September 18 | 4b |
| 59625 | June 6 | September 12 | 4b (est.) |
| 59623 | June 6 | September 12 | 5a |
Which crops fit a 98-day season in Helena
In Helena (98 frost-free days, a short season), 29 of 56 planner crops fit outright, 14 get two plantings, 5 need an indoor start, 7 don't reliably mature, 1 crop is perennial.
| Crop | Start indoors | Plant out / sow | Days you have | Verdict | Last sow date |
|---|---|---|---|---|---|
| Tomato | May 2 | Jun 20–Jun 27 | 56 | no-fit: Needs 80 days; Helena has 56 after Jun 20. | — |
| Pepper | Apr 25 | Jun 20–Jun 27 | 56 | head-start: Even planted out Jun 20, the outdoor season is about 19 days short; choose an early variety or grow under cover. | — |
| Lettuce | Apr 11 | May 9–May 16 | 133 | two-plantings: Plant May 9 and again by Jul 22; both mature before Sep 19. | Jul 22 |
| Carrots | — | May 16–May 23 | 140 | fits: 70 days to maturity, 140 available after May 16. | Jul 11 |
| Cucumber | May 16 | Jun 20–Jun 27 | 70 | fits: 60 days to maturity, 70 available after Jun 20. | — |
| Beans | — | Jun 13–Jun 27 | 84 | fits: 60 days to maturity, 84 available after Jun 13. | Jun 23 |
| Peas | — | Apr 11–Jun 20 | 161 | fits: 65 days to maturity, 161 available after Apr 11. | Jul 2 |
| Zucchini | May 23 | Jun 20–Jun 27 | 70 | fits: 55 days to maturity, 70 available after Jun 20. | Jun 21 |
| Onion | Mar 14 | May 9–May 23 | 133 | fits: 100 days to maturity, 133 available after May 9. | — |
| Spinach | — | Apr 11–May 30 | 175 | two-plantings: Plant Apr 11 and again by Aug 10; both mature before Oct 3. | Aug 10 |
| Kale | Mar 28 | May 9–May 23 | 147 | two-plantings: Plant May 9 and again by Jul 26; both mature before Oct 3. | Jul 26 |
| Broccoli | Apr 11 | May 9–May 23 | 133 | fits: 80 days to maturity, 133 available after May 9. | Jun 17 |
| Cabbage | Apr 11 | May 9–May 23 | 147 | fits: 70 days to maturity, 147 available after May 9. | Jul 11 |
| Radish | — | Apr 11–Jul 4 | 161 | two-plantings: Plant Apr 11 and again by Aug 11; both mature before Sep 19. | Aug 11 |
| Beets | — | Apr 11–Jul 4 | 161 | two-plantings: Plant Apr 11 and again by Jul 12; both mature before Sep 19. | Jul 12 |
| Potatoes | — | May 23–May 30 | 119 | fits: 90 days to maturity, 119 available after May 23. | — |
| Garlic | — | Sep 12 | 203 | overwinter: Plant Sep 12 to Oct 3; harvest the following summer. | Oct 3 |
| Strawberry | — | May 2–Jun 27 | 154 | perennial: A perennial: plant May 2; it fruits from the following year and keeps producing for several years. | — |
| Corn | May 9 | Jun 13–Jun 20 | 70 | head-start: Even planted out Jun 13, the outdoor season is about 5 days short; choose an early variety or grow under cover. | — |
| Pumpkin | May 23 | Jun 20–Jun 20 | 63 | no-fit: Needs 100 days; Helena has 63 after Jun 20. | — |
| Cauliflower | Apr 25 | May 30–Jun 13 | 112 | fits: 75 days to maturity, 112 available after May 30. | Jun 22 |
| Swiss Chard | Apr 11 | May 23–May 23 | 119 | fits: 55 days to maturity, 119 available after May 23. | Jul 12 |
| Arugula | — | Apr 11–Jul 4 | 175 | two-plantings: Plant Apr 11 and again by Aug 10; both mature before Oct 3. | Aug 10 |
| Brussel Sprouts | Apr 11 | May 9–May 23 | 147 | fits: 100 days to maturity, 147 available after May 9. | Jun 11 |
| Butternut Squash | May 23 | Jun 20–Jun 27 | 63 | no-fit: Needs 100 days; Helena has 63 after Jun 20. | — |
| Eggplant | Apr 18 | Jun 20–Jun 27 | 56 | head-start: Even planted out Jun 20, the outdoor season is about 14 days short; choose an early variety or grow under cover. | — |
| Okra | May 9 | Jun 13–Jun 20 | 77 | fits: 55 days to maturity, 77 available after Jun 13. | Jun 21 |
| Basil | May 2 | Jun 27–Jun 27 | 63 | fits: 60 days to maturity, 63 available after Jun 27. | — |
| Cilantro | — | May 9–May 30 | 133 | two-plantings: Plant May 9 and again by Jul 17; both mature before Sep 19. | Jul 17 |
| Parsley | Mar 28 | Jun 13–Jun 20 | 98 | fits: 70 days to maturity, 98 available after Jun 13. | Jun 27 |
| Celery | Mar 28 | Jun 13–Jun 27 | 98 | no-fit: Needs 120 days; Helena has 98 after Jun 13. | — |
| Scallions | Mar 28 | May 9–May 23 | 147 | two-plantings: Plant May 9 and again by Jul 21; both mature before Oct 3. | Jul 21 |
| Turnip | — | May 9–May 23 | 147 | two-plantings: Plant May 9 and again by Jul 31; both mature before Oct 3. | Jul 31 |
| Kohlrabi | — | Apr 25–May 9 | 161 | two-plantings: Plant Apr 25 and again by Jul 26; both mature before Oct 3. | Jul 26 |
| Bok Choy | May 9 | May 30–Jun 6 | 112 | two-plantings: Plant May 30 and again by Jul 22; both mature before Sep 19. | Jul 22 |
| Collards | Mar 28 | May 9–May 23 | 147 | two-plantings: Plant May 9 and again by Jul 21; both mature before Oct 3. | Jul 21 |
| Cantaloupe | May 23 | Jun 20–Jun 27 | 56 | no-fit: Needs 85 days; Helena has 56 after Jun 20. | — |
| Chives | Mar 14 | Jun 13–Jun 20 | 112 | fits: 90 days to maturity, 112 available after Jun 13. | — |
| Dill | — | Apr 11–Jul 4 | 161 | two-plantings: Plant Apr 11 and again by Jul 12; both mature before Sep 19. | Jul 12 |
| Oregano | Mar 28 | Jun 13–Jun 20 | 112 | fits: 80 days to maturity, 112 available after Jun 13. | — |
| Rosemary | Mar 14 | Jun 13–Jun 20 | 98 | fits: 80 days to maturity, 98 available after Jun 13. | — |
| Sage | Apr 11 | Jun 13–Jun 20 | 112 | fits: 75 days to maturity, 112 available after Jun 13. | — |
| Thyme | Mar 28 | Jun 13–Jun 20 | 112 | fits: 90 days to maturity, 112 available after Jun 13. | — |
| Calendula | Apr 25 | May 23–Jun 6 | 119 | two-plantings: Plant May 23 and again by Jul 17; both mature before Sep 19. | Jul 17 |
| Cosmos | May 9 | Jun 6–Jun 20 | 84 | fits: 60 days to maturity, 84 available after Jun 6. | Jun 16 |
| Lavender | Mar 14 | Jun 6–Jun 20 | 119 | fits: 90 days to maturity, 119 available after Jun 6. | — |
| Marigolds | Apr 25 | Jun 6–Jun 13 | 84 | fits: 50 days to maturity, 84 available after Jun 6. | Jun 26 |
| Melons | May 23 | Jun 20–Jun 27 | 56 | no-fit: Needs 85 days; Helena has 56 after Jun 20. | — |
| Mint | — | Jun 6–Jun 20 | 119 | fits: 90 days to maturity, 119 available after Jun 6. | — |
| Nasturtiums | May 9 | Jun 6–Jun 13 | 84 | fits: 55 days to maturity, 84 available after Jun 6. | Jun 21 |
| Pole Beans | — | Jun 13–Jun 27 | 77 | fits: 65 days to maturity, 77 available after Jun 13. | — |
| Spaghetti Squash | May 23 | Jun 20–Jun 27 | 63 | no-fit: Needs 90 days; Helena has 63 after Jun 20. | — |
| Sunflowers | — | Jun 6–Jun 20 | 84 | fits: 70 days to maturity, 84 available after Jun 6. | — |
| Tomatillos | Apr 11 | Jun 13–Jun 20 | 63 | head-start: Even planted out Jun 13, the outdoor season is about 12 days short; choose an early variety or grow under cover. | — |
| Watermelon | May 23 | Jun 13–Jun 20 | 63 | head-start: Even planted out Jun 13, the outdoor season is about 17 days short; choose an early variety or grow under cover. | — |
| Yellow Squash | May 23 | Jun 20–Jun 27 | 70 | fits: 55 days to maturity, 70 available after Jun 20. | Jun 21 |
| Zinnias | May 9 | Jun 6–Jun 20 | 84 | fits: 60 days to maturity, 84 available after Jun 6. | Jun 16 |
Month by month in Helena
| Month | What to do |
|---|---|
| January | Plan your garden layout and order seeds. Research varieties suited to your frost dates. |
| February | Start the slowest-growing crops indoors: onions, leeks, and celery (10–12 weeks before last frost). |
| March | Start indoors: Chives (Mar 14), Lavender (Mar 14), Onion (Mar 14), Rosemary (Mar 14), Celery (Mar 28), Collards (Mar 28), +5 more. |
| April | Start indoors: Broccoli (Apr 11), Brussel Sprouts (Apr 11), Cabbage (Apr 11), Lettuce (Apr 11), Sage (Apr 11), Swiss Chard (Apr 11), +6 more. Direct sow from: Arugula (Apr 11), Beets (Apr 11), Dill (Apr 11), Peas (Apr 11), Radish (Apr 11), Spinach (Apr 11), +1 more. |
| May | Start indoors: Basil (May 2), Tomato (May 2), Bok Choy (May 9), Corn (May 9), Cosmos (May 9), Nasturtiums (May 9), +11 more. Direct sow from: Cilantro (May 9), Turnip (May 9), Carrots (May 16), Potatoes (May 23). Transplant from: Broccoli (May 9), Brussel Sprouts (May 9), Cabbage (May 9), Collards (May 9), Kale (May 9), Lettuce (May 9), +6 more. Plant: Strawberry (May 2). |
| June | Direct sow from: Sunflowers (Jun 6), Beans (Jun 13), Pole Beans (Jun 13). Transplant from: Cosmos (Jun 6), Lavender (Jun 6), Marigolds (Jun 6), Mint (Jun 6), Nasturtiums (Jun 6), Zinnias (Jun 6), +23 more. Last frost around June 6. Last sowing dates: Brussel Sprouts (Jun 11), Cosmos (Jun 16), Zinnias (Jun 16), Broccoli (Jun 17), Nasturtiums (Jun 21), Okra (Jun 21), +6 more. |
| July | Last sowing dates: Peas (Jul 2), Cabbage (Jul 11), Carrots (Jul 11), Beets (Jul 12), Dill (Jul 12), Swiss Chard (Jul 12), +9 more. |
| August | Last sowing dates: Arugula (Aug 10), Spinach (Aug 10), Radish (Aug 11). |
| September | Direct sow from: Garlic (Sep 12). First frost around September 12. |
| October | Last sowing dates: Garlic (Oct 3). |
| November | Clean up spent plants. Add compost to beds. Rest, review, and plan next year's garden. |
| 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 Helena, MT (ZIP 59601)?
The median last spring frost date for Helena, MT (ZIP code 59601) is around June 6. 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 May 21; one in ten it runs past June 21.
What is the first fall frost date in Helena, MT?
The median first fall frost date for Helena, MT is around September 12. 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 August 31 in the earliest one-in-ten years, so cover tomatoes and peppers from then.
How long is the growing season in Helena, MT?
The frost-free growing season in Helena is about 98 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 Helena (98 frost-free days, a short season), 29 of 56 planner crops fit outright, 14 get two plantings, 5 need an indoor start, 7 don't reliably mature, 1 crop is perennial.
What USDA hardiness zone is Helena, MT?
Helena, MT is in USDA hardiness zone 4b (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 Helena, MT?
Start tomatoes indoors May 2 and plant out Jun 20 in Helena. The planner uses the local median last frost and this crop's indoor-start and transplant offsets.
How many plantings of lettuce fit in Helena?
Two: plant May 9 and again by Jul 22; both mature before Sep 19.
When do I plant garlic in Helena?
Sep 12 to Oct 3; it overwinters and is ready the following summer.
Can I grow Celery in Helena?
Not reliably outdoors. Needs 120 days; Helena has 98 after Jun 13.
Which nearby ZIP has a longer season?
Great Falls (ZIP 59405) has 113 frost-free days, 15 more than Helena (ZIP 59601). See Great Falls ZIP 59405 frost dates
Nearby and related
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