Fall in zone 4bPhoto: Dietmar Rabich, CC BY-SA 4.0, via Wikimedia Commons
Frost dates for ZIP 59421 (Hardy, MT)
Average last spring and first fall frost dates with 10%, 50% and 90% odds, from NOAA's 1991–2020 climate normals for the nearest weather station, Adel, MT (5 miles away).
- Average last spring frostJun 450% chance of a 32°F freeze after this date
- Average first fall frostSep 1250% chance of a 32°F freeze by this date
- Growing season (frost-free)98 daysmedian, 32°F threshold
- USDA hardiness zone4b-25 to -20°F avg. coldest night
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Frost and freeze alerts from the NWS forecast for 59421, the spring soil-temperature heads-up for pre-emergent, and a short weekly yard-timing email.
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This week in your yard
As of Oct 18, 2026, from your frost dates, zone and soil temperature. Lawn timing · Vegetables · Pruning · Plants
Soil temperature now
2-inch depth
No soil station with a fresh reading within 62 miles.
4-inch depth
No soil station with a fresh reading within 62 miles.
Fall: Texas A&M AgriLife times fall pre-emergent (for winter weeds such as annual bluegrass) to soil cooling to about 70°F for several days. The 50–55°F band is the spring trigger. Always read and follow the product label.
7-day forecast and frost risk
The latest National Weather Service 7-day forecast and any Frost Advisory or Freeze Warning for 59421 load here. You can also open the NWS forecast for this ZIP.
Pre-emergent
No soil reading near this ZIP. Typical extension timing for your region: spring mid-April to mid-May.
Fertilizer window
Lawn region: Mountain West and High Plains. Timing only; always follow the product label.
- Kentucky bluegrass (cool-season): Early fall: Around Labor Day (late August–September); Late fall: Late October–November, before the ground freezes; Late spring: Optional around Memorial Day. Avoid: Early-spring and midsummer feeding (pushes top growth, favors crabgrass).
Plant now
No vegetable planting windows are open this week.
Prune now
No frost-timed pruning windows are open this week.
Spring-flowering shrubs are pruned right after their flowers fade, not by date. See the pruning guide.
Last spring frost odds
| Chance of a 32°F freeze after this date | Date |
|---|---|
| 90% (early: most years still freeze after this) | May 22 |
| 50% (the "average" last frost) | Jun 4 |
| 10% (cautious: only 1 year in 10 freezes later) | Jun 22 |
Most gardeners plant frost-tender crops (tomatoes, peppers, basil) after the 50% date, and closer to the 10% date for less risk.
First fall frost odds
| Chance the first 32°F freeze has happened by this date | Date |
|---|---|
| 10% (early: 1 year in 10 freezes this soon) | Aug 26 |
| 50% (the "average" first frost) | Sep 12 |
| 90% (late: most years have frozen by now) | Sep 28 |
Light frost, freeze and hard freeze
| Threshold | Last spring (50%) | First fall (50%) |
|---|---|---|
| 36°F (light frost possible on clear, calm nights) | n/a | n/a |
| 32°F (freeze) | Jun 4 | Sep 12 |
| 28°F (hard freeze) | May 16 | Sep 27 |
n/a means NOAA did not publish a date at that threshold for this station (usually because it rarely gets that cold).
Vegetable planting calendar for 59421
Dates count from your average last spring frost (Jun 4) and first fall frost (Sep 12). Half of years have a frost after the spring date, so give tender crops (tomatoes, peppers, squash) some slack.
| Crop | Start indoors | Spring planting | Fall planting |
|---|---|---|---|
| Tomato | Apr 9–23 | Jun 11–25 (transplant) | – |
| Pepper (sweet and hot) | Mar 26–Apr 9 | Jun 18–Jul 2 (transplant) | – |
| Eggplant | Mar 26–Apr 9 | Jun 18–Jul 2 (transplant) | – |
| Tomatillo | Apr 9–23 | Jun 11–25 (transplant) | – |
| Lettuce | Apr 9–23 | May 14–Jun 4 (transplant) May 7–Jun 18 (sow outdoors) | Jul 18–Aug 8 (transplant) Jul 4–Aug 1 (sowing) |
| Spinach | – | Apr 23–May 14 (sow outdoors) | Jul 18–Aug 8 (sowing) |
| Kale | Apr 9–23 | May 7–21 (transplant) May 7–21 (sow outdoors) | Jun 20–Jul 18 (transplant) Jun 6–Jul 4 (sowing) |
| Collards | Apr 9–23 | May 7–Jun 4 (transplant) May 7–Jun 4 (sow outdoors) | Jun 20–Jul 18 (transplant) Jun 6–Jul 4 (sowing) |
| Broccoli | Mar 26–Apr 9 | May 7–21 (transplant) | Jun 6–Jul 4 (transplant) |
| Cabbage | Mar 26–Apr 9 | May 7–21 (transplant) | Jun 6–Jul 4 (transplant) |
| Cauliflower | Mar 26–Apr 9 | May 21–Jun 4 (transplant) | Jun 6–Jul 4 (transplant) |
| Brussels sprouts | Mar 12–26 | May 7–21 (transplant) | May 23–Jun 13 (transplant) |
| Kohlrabi | Apr 9–23 | May 7–21 (transplant) May 7–21 (sow outdoors) | Jul 4–18 (sowing) |
| Bok choy / Asian greens | – | May 7–21 (sow outdoors) | Jul 18–Aug 1 (sowing) |
| Arugula | – | May 7–Jun 4 (sow outdoors) | Jul 18–Aug 15 (sowing) |
| Mustard greens | – | May 7–28 (sow outdoors) | Jul 18–Aug 1 (sowing) |
| Swiss chard | Apr 23–May 7 | May 21–Jun 11 (transplant) May 21–Jun 18 (sow outdoors) | Jul 4–18 (sowing) |
| Beet | – | May 7–Jun 4 (sow outdoors) | Jul 4–18 (sowing) |
| Carrot | – | May 14–Jun 11 (sow outdoors) | Jun 20–Jul 4 (sowing) |
| Radish | – | Apr 30–Jun 11 (sow outdoors) | Aug 1–15 (sowing) |
| Turnip | – | May 7–28 (sow outdoors) | Jul 4–18 (sowing) |
| Parsnip | – | May 14–Jun 4 (sow outdoors) | – |
| Pea (garden, snap, snow) | – | Apr 9–May 7 (sow outdoors) | Jun 20–Jul 4 (sowing) |
| Onion (bulbing) | Mar 12–26 | Apr 23–May 7 (transplant) | – |
| Green onion / scallion | – | Apr 23–May 21 (sow outdoors) | Jul 4–18 (sowing) |
| Leek | Mar 12–26 | May 7–21 (transplant) | – |
| Garlic | – | – | Aug 1–29 (sowing) |
| Shallot | – | Apr 23–May 7 (transplant) | Aug 1–29 (sowing) |
| Potato | – | May 7–21 (transplant) | May 23–Jun 6 (transplant) |
| Sweet potato | – | Jun 25–Jul 9 (transplant) | – |
| Sweet corn | – | Jun 11–25 (sow outdoors) | – |
| Bean, bush (snap) | – | Jun 11–25 (sow outdoors) | – |
| Bean, pole | – | Jun 11–25 (sow outdoors) | – |
| Lima bean | – | Jun 18–Jul 2 (sow outdoors) | – |
| Southern pea (cowpea, black-eyed pea) | – | Jun 25–Jul 16 (sow outdoors) | – |
| Cucumber | May 7–14 | Jun 11–25 (transplant) Jun 11–25 (sow outdoors) | – |
| Summer squash / zucchini | May 7–14 | Jun 11–25 (transplant) Jun 11–25 (sow outdoors) | – |
| Winter squash | May 7–14 | Jun 11–25 (transplant) Jun 11–25 (sow outdoors) | – |
| Pumpkin | – | Jun 11–25 (sow outdoors) | – |
| Watermelon | May 7–14 | Jun 18–Jul 2 (transplant) Jun 18–Jul 2 (sow outdoors) | – |
| Cantaloupe / muskmelon | May 7–14 | Jun 18–Jul 2 (transplant) Jun 18–Jul 2 (sow outdoors) | – |
| Okra | Apr 23–May 7 | Jun 18–Jul 2 (transplant) Jun 18–Jul 2 (sow outdoors) | – |
| Celery | Mar 12–26 | Jun 11–18 (transplant) | – |
| Basil | Apr 23–May 7 | Jun 11–25 (transplant) Jun 11–25 (sow outdoors) | – |
| Cilantro | – | May 21–Jun 18 (sow outdoors) | Jul 18–Aug 1 (sowing) |
| Parsley | Mar 26–Apr 9 | May 21–Jun 4 (transplant) May 14–Jun 4 (sow outdoors) | – |
| Dill | – | Jun 4–18 (sow outdoors) | Jul 18–Aug 1 (sowing) |
| Sunflower | – | Jun 4–18 (sow outdoors) | – |
| Asparagus (crowns) | – | May 7–21 (transplant) | – |
| Rhubarb (crowns) | – | May 7–21 (transplant) | – |
| Strawberry (plants) | – | May 7–21 (transplant) | Jul 4–Aug 1 (transplant) |
Typical ranges from university extension planting calendars, adjusted to your frost dates. Probabilities, not guarantees. Fall windows that would overlap spring planting are left out, as are fall crops of frost-tender plants where the frost-free season is under 210 days.
Where these numbers come from
Station: Adel, MT (NOAA GHCN-Daily ID USC00240056), elevation 5,017 ft, 4.6 miles from the ZIP's center point. NOAA completeness flag: E (estimated from nearby stations).
Nearby stations
| Station | Distance | Last frost (50%) | First frost (50%) |
|---|---|---|---|
| Cascade 5 S, MT | 10 mi | May 21 | Sep 19 |
| Holter Dam, MT | 16 mi | May 19 | Sep 24 |
| Sun Rvr 4 S, MT | 28 mi | Jun 2 | Sep 10 |
The average last-frost dates of these stations span 16 days, a rough guide to local variation. See data sources & methods.
Frost questions for 59421
When is the last frost in 59421?
The average (50% chance) last spring freeze of 32°F for ZIP 59421 is June 4. For a more cautious planting date, use June 22, when only 1 year in 10 still sees a later freeze.
When is the first frost in 59421?
The average first fall freeze is September 12. In 1 year in 10 it comes by August 26.
What hardiness zone is 59421?
ZIP 59421 is in USDA zone 4b (-25 to -20°F average coldest winter night), per the 2023 USDA Plant Hardiness Zone Map ZIP listing.
What is the soil temperature in 59421 right now?
This page shows the latest 2-inch and 4-inch soil temperature from the nearest public soil station (USDA SCAN, NOAA USCRN or TexMesonet), or a labeled estimate when no station is close, against the 50–55°F spring pre-emergent band.
Nearby ZIP codes
59405 Malmstrom AFB 59648 Milford Colony 59485 Ulm 59602 Helena Valley Northeast 59483 Sun River 59477 Simms 59472 Sand Coulee 59480 Stockett
Other ZIP codes in Cascade County
59401 59404 59405 59412 59414 59443 59463 59465 59472 59477 59480 59483 59485 59487 All Cascade County frost dates · Montana frost dates
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Weekly yard timing, plus frost and soil-temperature alerts for your ZIP code.
- Freeze alerts
- Soil-temp heads-up
- Weekly yard to-dos
Free. One weekly email plus alerts when your ZIP has a frost or a soil-temperature change worth acting on. After you submit, Kit (our email provider) sends a confirmation email: check your email and click the link to confirm. You aren't subscribed until you do. We collect only your email address and ZIP, sent to Kit to deliver The Dial. Unsubscribe anytime.