Frost Dates for Great Falls, MT 59405
Last spring frost May 24 · First fall frost September 14 · 113 frost-free days · USDA Zone 4b
ZIP 59405 has about 33,400 people, the largest of 3 ZIP codes in Great Falls.
Short season: 113 frost-free days. Spring frost risk spans May 8–June 8 (31 days). Fall frost risk spans September 3–September 26 (23 days).
Frost probability for 59405
| Frost | 10% | 50% | 90% |
|---|---|---|---|
| Spring (last frost) | June 8 | May 24 | May 8 |
| Fall (first frost) | September 3 | September 14 | September 26 |
Dates come from NOAA 1971–2000 freeze probabilities at CASCADE 5 S (34.8 km away); the 50% date is the median year.
Frost dates by ZIP code in Great Falls, MT
| ZIP | Last spring frost (50%) | First fall frost (50%) | Zone |
|---|---|---|---|
| 59405 | May 24 | September 14 | 4b |
| 59404 | May 24 | September 14 | 4b |
| 59401 | May 24 | September 14 | 4b |
Which crops fit a 113-day season in Great Falls
In Great Falls (113 frost-free days, a short season), 31 of 56 planner crops fit outright, 15 get two plantings, 7 need an indoor start, 2 don't reliably mature, 1 crop is perennial.
| Crop | Start indoors | Plant out / sow | Days you have | Verdict | Last sow date |
|---|---|---|---|---|---|
| Tomato | Apr 19 | Jun 7–Jun 14 | 71 | head-start: Even planted out Jun 7, the outdoor season is about 9 days short; choose an early variety or grow under cover. | — |
| Pepper | Apr 12 | Jun 7–Jun 14 | 71 | head-start: Even planted out Jun 7, the outdoor season is about 4 days short; choose an early variety or grow under cover. | — |
| Lettuce | Mar 29 | Apr 26–May 3 | 148 | two-plantings: Plant Apr 26 and again by Jul 24; both mature before Sep 21. | Jul 24 |
| Carrots | — | May 3–May 10 | 155 | fits: 70 days to maturity, 155 available after May 3. | Jul 13 |
| Cucumber | May 3 | Jun 7–Jun 14 | 85 | fits: 60 days to maturity, 85 available after Jun 7. | Jun 18 |
| Beans | — | May 31–Jun 14 | 99 | fits: 60 days to maturity, 99 available after May 31. | Jun 25 |
| Peas | — | Mar 29–Jun 7 | 176 | fits: 65 days to maturity, 176 available after Mar 29. | Jul 4 |
| Zucchini | May 10 | Jun 7–Jun 14 | 85 | fits: 55 days to maturity, 85 available after Jun 7. | Jun 23 |
| Onion | Mar 1 | Apr 26–May 10 | 148 | fits: 100 days to maturity, 148 available after Apr 26. | — |
| Spinach | — | Mar 29–May 17 | 190 | two-plantings: Plant Mar 29 and again by Aug 12; both mature before Oct 5. | Aug 12 |
| Kale | Mar 15 | Apr 26–May 10 | 162 | two-plantings: Plant Apr 26 and again by Jul 28; both mature before Oct 5. | Jul 28 |
| Broccoli | Mar 29 | Apr 26–May 10 | 148 | fits: 80 days to maturity, 148 available after Apr 26. | Jun 19 |
| Cabbage | Mar 29 | Apr 26–May 10 | 162 | fits: 70 days to maturity, 162 available after Apr 26. | Jul 13 |
| Radish | — | Mar 29–Jun 21 | 176 | two-plantings: Plant Mar 29 and again by Aug 13; both mature before Sep 21. | Aug 13 |
| Beets | — | Mar 29–Jun 21 | 176 | two-plantings: Plant Mar 29 and again by Jul 14; both mature before Sep 21. | Jul 14 |
| Potatoes | — | May 10–May 17 | 134 | fits: 90 days to maturity, 134 available after May 10. | — |
| Garlic | — | Sep 14 | 218 | overwinter: Plant Sep 14 to Oct 5; harvest the following summer. | Oct 5 |
| Strawberry | — | Apr 19–Jun 14 | 169 | perennial: A perennial: plant Apr 19; it fruits from the following year and keeps producing for several years. | — |
| Corn | Apr 26 | May 31–Jun 7 | 85 | fits: 75 days to maturity, 85 available after May 31. | — |
| Pumpkin | May 10 | Jun 7–Jun 7 | 78 | no-fit: Needs 100 days; Great Falls has 78 after Jun 7. | — |
| Cauliflower | Apr 12 | May 17–May 31 | 127 | fits: 75 days to maturity, 127 available after May 17. | Jun 24 |
| Swiss Chard | Mar 29 | May 10–May 10 | 134 | two-plantings: Plant May 10 and again by Jul 14; both mature before Sep 21. | Jul 14 |
| Arugula | — | Mar 29–Jun 21 | 190 | two-plantings: Plant Mar 29 and again by Aug 12; both mature before Oct 5. | Aug 12 |
| Brussel Sprouts | Mar 29 | Apr 26–May 10 | 162 | fits: 100 days to maturity, 162 available after Apr 26. | Jun 13 |
| Butternut Squash | May 10 | Jun 7–Jun 14 | 78 | no-fit: Needs 100 days; Great Falls has 78 after Jun 7. | — |
| Eggplant | Apr 5 | Jun 7–Jun 14 | 71 | fits: 70 days to maturity, 71 available after Jun 7. | — |
| Okra | Apr 26 | May 31–Jun 7 | 92 | fits: 55 days to maturity, 92 available after May 31. | Jun 23 |
| Basil | Apr 19 | Jun 14–Jun 14 | 78 | fits: 60 days to maturity, 78 available after Jun 14. | Jun 18 |
| Cilantro | — | Apr 26–May 17 | 148 | two-plantings: Plant Apr 26 and again by Jul 19; both mature before Sep 21. | Jul 19 |
| Parsley | Mar 15 | May 31–Jun 7 | 113 | fits: 70 days to maturity, 113 available after May 31. | Jun 29 |
| Celery | Mar 15 | May 31–Jun 14 | 113 | head-start: Even planted out May 31, the outdoor season is about 7 days short; choose an early variety or grow under cover. | — |
| Scallions | Mar 15 | Apr 26–May 10 | 162 | two-plantings: Plant Apr 26 and again by Jul 23; both mature before Oct 5. | Jul 23 |
| Turnip | — | Apr 26–May 10 | 162 | two-plantings: Plant Apr 26 and again by Aug 2; both mature before Oct 5. | Aug 2 |
| Kohlrabi | — | Apr 12–Apr 26 | 176 | two-plantings: Plant Apr 12 and again by Jul 28; both mature before Oct 5. | Jul 28 |
| Bok Choy | Apr 26 | May 17–May 24 | 127 | two-plantings: Plant May 17 and again by Jul 24; both mature before Sep 21. | Jul 24 |
| Collards | Mar 15 | Apr 26–May 10 | 162 | two-plantings: Plant Apr 26 and again by Jul 23; both mature before Oct 5. | Jul 23 |
| Cantaloupe | May 10 | Jun 7–Jun 14 | 71 | head-start: Even planted out Jun 7, the outdoor season is about 14 days short; choose an early variety or grow under cover. | — |
| Chives | Mar 1 | May 31–Jun 7 | 127 | fits: 90 days to maturity, 127 available after May 31. | — |
| Dill | — | Mar 29–Jun 21 | 176 | two-plantings: Plant Mar 29 and again by Jul 14; both mature before Sep 21. | Jul 14 |
| Oregano | Mar 15 | May 31–Jun 7 | 127 | fits: 80 days to maturity, 127 available after May 31. | — |
| Rosemary | Mar 1 | May 31–Jun 7 | 113 | fits: 80 days to maturity, 113 available after May 31. | — |
| Sage | Mar 29 | May 31–Jun 7 | 127 | fits: 75 days to maturity, 127 available after May 31. | — |
| Thyme | Mar 15 | May 31–Jun 7 | 127 | fits: 90 days to maturity, 127 available after May 31. | — |
| Calendula | Apr 12 | May 10–May 24 | 134 | two-plantings: Plant May 10 and again by Jul 19; both mature before Sep 21. | Jul 19 |
| Cosmos | Apr 26 | May 24–Jun 7 | 99 | fits: 60 days to maturity, 99 available after May 24. | Jun 18 |
| Lavender | Mar 1 | May 24–Jun 7 | 134 | fits: 90 days to maturity, 134 available after May 24. | — |
| Marigolds | Apr 12 | May 24–May 31 | 99 | fits: 50 days to maturity, 99 available after May 24. | Jun 28 |
| Melons | May 10 | Jun 7–Jun 14 | 71 | head-start: Even planted out Jun 7, the outdoor season is about 14 days short; choose an early variety or grow under cover. | — |
| Mint | — | May 24–Jun 7 | 134 | fits: 90 days to maturity, 134 available after May 24. | — |
| Nasturtiums | Apr 26 | May 24–May 31 | 99 | fits: 55 days to maturity, 99 available after May 24. | Jun 23 |
| Pole Beans | — | May 31–Jun 14 | 92 | fits: 65 days to maturity, 92 available after May 31. | Jun 13 |
| Spaghetti Squash | May 10 | Jun 7–Jun 14 | 78 | head-start: Even planted out Jun 7, the outdoor season is about 12 days short; choose an early variety or grow under cover. | — |
| Sunflowers | — | May 24–Jun 7 | 99 | fits: 70 days to maturity, 99 available after May 24. | Jun 8 |
| Tomatillos | Mar 29 | May 31–Jun 7 | 78 | fits: 75 days to maturity, 78 available after May 31. | — |
| Watermelon | May 10 | May 31–Jun 7 | 78 | head-start: Even planted out May 31, the outdoor season is about 2 days short; choose an early variety or grow under cover. | — |
| Yellow Squash | May 10 | Jun 7–Jun 14 | 85 | fits: 55 days to maturity, 85 available after Jun 7. | Jun 23 |
| Zinnias | Apr 26 | May 24–Jun 7 | 99 | fits: 60 days to maturity, 99 available after May 24. | Jun 18 |
Month by month in Great Falls
| 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 1), Lavender (Mar 1), Onion (Mar 1), Rosemary (Mar 1), Celery (Mar 15), Collards (Mar 15), +12 more. Direct sow from: Arugula (Mar 29), Beets (Mar 29), Dill (Mar 29), Peas (Mar 29), Radish (Mar 29), Spinach (Mar 29). |
| April | Start indoors: Eggplant (Apr 5), Calendula (Apr 12), Cauliflower (Apr 12), Marigolds (Apr 12), Pepper (Apr 12), Basil (Apr 19), +7 more. Direct sow from: Kohlrabi (Apr 12), Cilantro (Apr 26), Turnip (Apr 26). Transplant from: Broccoli (Apr 26), Brussel Sprouts (Apr 26), Cabbage (Apr 26), Collards (Apr 26), Kale (Apr 26), Lettuce (Apr 26), +2 more. Plant: Strawberry (Apr 19). |
| May | Start indoors: Cucumber (May 3), Butternut Squash (May 10), Cantaloupe (May 10), Melons (May 10), Pumpkin (May 10), Spaghetti Squash (May 10), +3 more. Direct sow from: Carrots (May 3), Potatoes (May 10), Sunflowers (May 24), Beans (May 31), Pole Beans (May 31). Transplant from: Calendula (May 10), Swiss Chard (May 10), Bok Choy (May 17), Cauliflower (May 17), Cosmos (May 24), Lavender (May 24), +15 more. Last frost around May 24. |
| June | Transplant from: Butternut Squash (Jun 7), Cantaloupe (Jun 7), Cucumber (Jun 7), Eggplant (Jun 7), Melons (Jun 7), Pepper (Jun 7), +6 more. Last sowing dates: Sunflowers (Jun 8), Brussel Sprouts (Jun 13), Pole Beans (Jun 13), Basil (Jun 18), Cosmos (Jun 18), Cucumber (Jun 18), +10 more. |
| July | Last sowing dates: Peas (Jul 4), Cabbage (Jul 13), Carrots (Jul 13), Beets (Jul 14), Dill (Jul 14), Swiss Chard (Jul 14), +8 more. |
| August | Last sowing dates: Turnip (Aug 2), Arugula (Aug 12), Spinach (Aug 12), Radish (Aug 13). |
| September | Direct sow from: Garlic (Sep 14). First frost around September 14. |
| October | Last sowing dates: Garlic (Oct 5). |
| 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 Great Falls, MT (ZIP 59405)?
The median last spring frost date for Great Falls, MT (ZIP code 59405) is around May 24. 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 8; one in ten it runs past June 8.
What is the first fall frost date in Great Falls, MT?
The median first fall frost date for Great Falls, MT is around September 14. 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 3 in the earliest one-in-ten years, so cover tomatoes and peppers from then.
How long is the growing season in Great Falls, MT?
The frost-free growing season in Great Falls is about 113 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 Great Falls (113 frost-free days, a short season), 31 of 56 planner crops fit outright, 15 get two plantings, 7 need an indoor start, 2 don't reliably mature, 1 crop is perennial.
What USDA hardiness zone is Great Falls, MT?
Great Falls, 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 Great Falls, MT?
Start tomatoes indoors Apr 19 and plant out Jun 7 in Great Falls. The planner uses the local median last frost and this crop's indoor-start and transplant offsets.
How many plantings of lettuce fit in Great Falls?
Two: plant Apr 26 and again by Jul 24; both mature before Sep 21.
When do I plant garlic in Great Falls?
Sep 14 to Oct 5; it overwinters and is ready the following summer.
Can I grow Celery in Great Falls?
Yes, with help. Even planted out May 31, the outdoor season is about 7 days short; choose an early variety or grow under cover.
Nearby and related
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