Frost Dates for Helena, MT 59602
Helena has 4 ZIP codes. The Helena, MT frost page lists all of them with their dates.
Last spring frost May 19 · First fall frost September 18 · 122 frost-free days · USDA Zone 4b
ZIP 59602 has about 30,800 people, one of 4 ZIP codes in Helena.
Moderate season: 122 frost-free days. Spring frost risk spans May 3–June 4 (32 days). Fall frost risk spans September 6–September 29 (23 days).
Frost probability for 59602
| Frost | 10% | 50% | 90% |
|---|---|---|---|
| Spring (last frost) | June 4 | May 19 | May 3 |
| Fall (first frost) | September 6 | September 18 | September 29 |
Dates come from NOAA 1971–2000 freeze probabilities at HELENA AP ASOS (15.9 km away); the 50% date is the median year.
Which crops fit a 122-day season in Helena
In Helena (122 frost-free days, a moderate season), 35 of 56 planner crops fit outright, 15 get two plantings, 5 need an indoor start, 1 crop is perennial.
| Crop | Start indoors | Plant out / sow | Days you have | Verdict | Last sow date |
|---|---|---|---|---|---|
| Tomato | Apr 14 | Jun 2–Jun 9 | 80 | fits: 80 days to maturity, 80 available after Jun 2. | — |
| Pepper | Apr 7 | Jun 2–Jun 9 | 80 | fits: 75 days to maturity, 80 available after Jun 2. | — |
| Lettuce | Mar 24 | Apr 21–Apr 28 | 157 | two-plantings: Plant Apr 21 and again by Jul 28; both mature before Sep 25. | Jul 28 |
| Carrots | — | Apr 28–May 5 | 164 | fits: 70 days to maturity, 164 available after Apr 28. | Jul 17 |
| Cucumber | Apr 28 | Jun 2–Jun 9 | 94 | fits: 60 days to maturity, 94 available after Jun 2. | Jun 22 |
| Beans | — | May 26–Jun 9 | 108 | fits: 60 days to maturity, 108 available after May 26. | Jun 29 |
| Peas | — | Mar 24–Jun 2 | 185 | fits: 65 days to maturity, 185 available after Mar 24. | Jul 8 |
| Zucchini | May 5 | Jun 2–Jun 9 | 94 | fits: 55 days to maturity, 94 available after Jun 2. | Jun 27 |
| Onion | Feb 24 | Apr 21–May 5 | 157 | fits: 100 days to maturity, 157 available after Apr 21. | — |
| Spinach | — | Mar 24–May 12 | 199 | two-plantings: Plant Mar 24 and again by Aug 16; both mature before Oct 9. | Aug 16 |
| Kale | Mar 10 | Apr 21–May 5 | 171 | two-plantings: Plant Apr 21 and again by Aug 1; both mature before Oct 9. | Aug 1 |
| Broccoli | Mar 24 | Apr 21–May 5 | 157 | fits: 80 days to maturity, 157 available after Apr 21. | Jun 23 |
| Cabbage | Mar 24 | Apr 21–May 5 | 171 | fits: 70 days to maturity, 171 available after Apr 21. | Jul 17 |
| Radish | — | Mar 24–Jun 16 | 185 | two-plantings: Plant Mar 24 and again by Aug 17; both mature before Sep 25. | Aug 17 |
| Beets | — | Mar 24–Jun 16 | 185 | two-plantings: Plant Mar 24 and again by Jul 18; both mature before Sep 25. | Jul 18 |
| Potatoes | — | May 5–May 12 | 143 | fits: 90 days to maturity, 143 available after May 5. | — |
| Garlic | — | Sep 18 | 227 | overwinter: Plant Sep 18 to Oct 9; harvest the following summer. | Oct 9 |
| Strawberry | — | Apr 14–Jun 9 | 178 | perennial: A perennial: plant Apr 14; it fruits from the following year and keeps producing for several years. | — |
| Corn | Apr 21 | May 26–Jun 2 | 94 | fits: 75 days to maturity, 94 available after May 26. | May 31 |
| Pumpkin | May 5 | Jun 2–Jun 2 | 87 | head-start: Even planted out Jun 2, the outdoor season is about 13 days short; choose an early variety or grow under cover. | — |
| Cauliflower | Apr 7 | May 12–May 26 | 136 | fits: 75 days to maturity, 136 available after May 12. | Jun 28 |
| Swiss Chard | Mar 24 | May 5–May 5 | 143 | two-plantings: Plant May 5 and again by Jul 18; both mature before Sep 25. | Jul 18 |
| Arugula | — | Mar 24–Jun 16 | 199 | two-plantings: Plant Mar 24 and again by Aug 16; both mature before Oct 9. | Aug 16 |
| Brussel Sprouts | Mar 24 | Apr 21–May 5 | 171 | fits: 100 days to maturity, 171 available after Apr 21. | Jun 17 |
| Butternut Squash | May 5 | Jun 2–Jun 9 | 87 | head-start: Even planted out Jun 2, the outdoor season is about 13 days short; choose an early variety or grow under cover. | — |
| Eggplant | Mar 31 | Jun 2–Jun 9 | 80 | fits: 70 days to maturity, 80 available after Jun 2. | — |
| Okra | Apr 21 | May 26–Jun 2 | 101 | fits: 55 days to maturity, 101 available after May 26. | Jun 27 |
| Basil | Apr 14 | Jun 9–Jun 9 | 87 | fits: 60 days to maturity, 87 available after Jun 9. | Jun 22 |
| Cilantro | — | Apr 21–May 12 | 157 | two-plantings: Plant Apr 21 and again by Jul 23; both mature before Sep 25. | Jul 23 |
| Parsley | Mar 10 | May 26–Jun 2 | 122 | fits: 70 days to maturity, 122 available after May 26. | Jul 3 |
| Celery | Mar 10 | May 26–Jun 9 | 122 | fits: 120 days to maturity, 122 available after May 26. | — |
| Scallions | Mar 10 | Apr 21–May 5 | 171 | two-plantings: Plant Apr 21 and again by Jul 27; both mature before Oct 9. | Jul 27 |
| Turnip | — | Apr 21–May 5 | 171 | two-plantings: Plant Apr 21 and again by Aug 6; both mature before Oct 9. | Aug 6 |
| Kohlrabi | — | Apr 7–Apr 21 | 185 | two-plantings: Plant Apr 7 and again by Aug 1; both mature before Oct 9. | Aug 1 |
| Bok Choy | Apr 21 | May 12–May 19 | 136 | two-plantings: Plant May 12 and again by Jul 28; both mature before Sep 25. | Jul 28 |
| Collards | Mar 10 | Apr 21–May 5 | 171 | two-plantings: Plant Apr 21 and again by Jul 27; both mature before Oct 9. | Jul 27 |
| Cantaloupe | May 5 | Jun 2–Jun 9 | 80 | head-start: Even planted out Jun 2, the outdoor season is about 5 days short; choose an early variety or grow under cover. | — |
| Chives | Feb 24 | May 26–Jun 2 | 136 | fits: 90 days to maturity, 136 available after May 26. | — |
| Dill | — | Mar 24–Jun 16 | 185 | two-plantings: Plant Mar 24 and again by Jul 18; both mature before Sep 25. | Jul 18 |
| Oregano | Mar 10 | May 26–Jun 2 | 136 | fits: 80 days to maturity, 136 available after May 26. | — |
| Rosemary | Feb 24 | May 26–Jun 2 | 122 | fits: 80 days to maturity, 122 available after May 26. | — |
| Sage | Mar 24 | May 26–Jun 2 | 136 | fits: 75 days to maturity, 136 available after May 26. | — |
| Thyme | Mar 10 | May 26–Jun 2 | 136 | fits: 90 days to maturity, 136 available after May 26. | — |
| Calendula | Apr 7 | May 5–May 19 | 143 | two-plantings: Plant May 5 and again by Jul 23; both mature before Sep 25. | Jul 23 |
| Cosmos | Apr 21 | May 19–Jun 2 | 108 | fits: 60 days to maturity, 108 available after May 19. | Jun 22 |
| Lavender | Feb 24 | May 19–Jun 2 | 143 | fits: 90 days to maturity, 143 available after May 19. | — |
| Marigolds | Apr 7 | May 19–May 26 | 108 | fits: 50 days to maturity, 108 available after May 19. | Jul 2 |
| Melons | May 5 | Jun 2–Jun 9 | 80 | head-start: Even planted out Jun 2, the outdoor season is about 5 days short; choose an early variety or grow under cover. | — |
| Mint | — | May 19–Jun 2 | 143 | fits: 90 days to maturity, 143 available after May 19. | — |
| Nasturtiums | Apr 21 | May 19–May 26 | 108 | fits: 55 days to maturity, 108 available after May 19. | Jun 27 |
| Pole Beans | — | May 26–Jun 9 | 101 | fits: 65 days to maturity, 101 available after May 26. | Jun 17 |
| Spaghetti Squash | May 5 | Jun 2–Jun 9 | 87 | head-start: Even planted out Jun 2, the outdoor season is about 3 days short; choose an early variety or grow under cover. | — |
| Sunflowers | — | May 19–Jun 2 | 108 | fits: 70 days to maturity, 108 available after May 19. | Jun 12 |
| Tomatillos | Mar 24 | May 26–Jun 2 | 87 | fits: 75 days to maturity, 87 available after May 26. | — |
| Watermelon | May 5 | May 26–Jun 2 | 87 | fits: 80 days to maturity, 87 available after May 26. | — |
| Yellow Squash | May 5 | Jun 2–Jun 9 | 94 | fits: 55 days to maturity, 94 available after Jun 2. | Jun 27 |
| Zinnias | Apr 21 | May 19–Jun 2 | 108 | fits: 60 days to maturity, 108 available after May 19. | Jun 22 |
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 indoors: Chives (Feb 24), Lavender (Feb 24), Onion (Feb 24), Rosemary (Feb 24). |
| March | Start indoors: Celery (Mar 10), Collards (Mar 10), Kale (Mar 10), Oregano (Mar 10), Parsley (Mar 10), Scallions (Mar 10), +9 more. Direct sow from: Arugula (Mar 24), Beets (Mar 24), Dill (Mar 24), Peas (Mar 24), Radish (Mar 24), Spinach (Mar 24). |
| April | Start indoors: Calendula (Apr 7), Cauliflower (Apr 7), Marigolds (Apr 7), Pepper (Apr 7), Basil (Apr 14), Tomato (Apr 14), +7 more. Direct sow from: Kohlrabi (Apr 7), Cilantro (Apr 21), Turnip (Apr 21), Carrots (Apr 28). Transplant from: Broccoli (Apr 21), Brussel Sprouts (Apr 21), Cabbage (Apr 21), Collards (Apr 21), Kale (Apr 21), Lettuce (Apr 21), +2 more. Plant: Strawberry (Apr 14). |
| May | Start indoors: Butternut Squash (May 5), Cantaloupe (May 5), Melons (May 5), Pumpkin (May 5), Spaghetti Squash (May 5), Watermelon (May 5), +2 more. Direct sow from: Potatoes (May 5), Sunflowers (May 19), Beans (May 26), Pole Beans (May 26). Transplant from: Calendula (May 5), Swiss Chard (May 5), Bok Choy (May 12), Cauliflower (May 12), Cosmos (May 19), Lavender (May 19), +15 more. Last frost around May 19. Last sowing dates: Corn (May 31). |
| June | Transplant from: Butternut Squash (Jun 2), Cantaloupe (Jun 2), Cucumber (Jun 2), Eggplant (Jun 2), Melons (Jun 2), Pepper (Jun 2), +6 more. Last sowing dates: Sunflowers (Jun 12), Brussel Sprouts (Jun 17), Pole Beans (Jun 17), Basil (Jun 22), Cosmos (Jun 22), Cucumber (Jun 22), +8 more. |
| July | Last sowing dates: Marigolds (Jul 2), Parsley (Jul 3), Peas (Jul 8), Cabbage (Jul 17), Carrots (Jul 17), Beets (Jul 18), +8 more. |
| August | Last sowing dates: Kale (Aug 1), Kohlrabi (Aug 1), Turnip (Aug 6), Arugula (Aug 16), Spinach (Aug 16), Radish (Aug 17). |
| September | Direct sow from: Garlic (Sep 18). First frost around September 18. |
| October | Last sowing dates: Garlic (Oct 9). |
| 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 59602)?
The median last spring frost date for Helena, MT (ZIP code 59602) is around May 19. 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 3; one in ten it runs past June 4.
What is the first fall frost date in Helena, MT?
The median first fall frost date for Helena, MT is around September 18. 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 6 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 122 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 (122 frost-free days, a moderate season), 35 of 56 planner crops fit outright, 15 get two plantings, 5 need an indoor start, 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 Apr 14 and plant out Jun 2 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 Apr 21 and again by Jul 28; both mature before Sep 25.
When do I plant garlic in Helena?
Sep 18 to Oct 9; it overwinters and is ready the following summer.
Can I grow Butternut Squash in Helena?
Yes, with help. Even planted out Jun 2, the outdoor season is about 13 days short; choose an early variety or grow under cover.
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