Fall in zone 4bPhoto: Dietmar Rabich, CC BY-SA 4.0, via Wikimedia Commons
Frost dates for ZIP 59638 (Jefferson City, 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, Tizer Gardens, MT (1 miles away).
- Average last spring frostJun 1850% chance of a 32°F freeze after this date
- Average first fall frostSep 550% chance of a 32°F freeze by this date
- Growing season (frost-free)81 daysmedian, 32°F threshold
- USDA hardiness zone4b-25 to -20°F avg. coldest night
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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
44°F Below 50°F
24-hour average · latest 45°F, as of Oct 18, 2:00 AM CDT
Estimate Not a measurement at this ZIP: distance-weighted average of Table Mountain (44 mi).
4-inch depth
43°F Below 50°F
24-hour average · latest 46°F, as of Oct 18, 2:00 AM CDT
Estimate Not a measurement at this ZIP: distance-weighted average of Table Mountain (44 mi).
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 59638 load here. You can also open the NWS forecast for this ZIP.
Pre-emergent
Soil is 43°F at 4 inches (estimated soil temperature, not a station reading). Fall pre-emergent window is mostly past. Next: spring, when soil reaches 50°F (typically 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 30 |
| 50% (the "average" last frost) | Jun 18 |
| 10% (cautious: only 1 year in 10 freezes later) | Jul 3 |
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 21 |
| 50% (the "average" first frost) | Sep 5 |
| 90% (late: most years have frozen by now) | Sep 18 |
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 18 | Sep 5 |
| 28°F (hard freeze) | May 29 | Sep 18 |
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 59638
Dates count from your average last spring frost (Jun 18) and first fall frost (Sep 5). 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 23–May 7 | Jun 25–Jul 9 (transplant) | – |
| Pepper (sweet and hot) | Apr 9–23 | Jul 2–16 (transplant) | – |
| Eggplant | Apr 9–23 | Jul 2–16 (transplant) | – |
| Tomatillo | Apr 23–May 7 | Jun 25–Jul 9 (transplant) | – |
| Lettuce | Apr 23–May 7 | May 28–Jun 18 (transplant) May 21–Jul 2 (sow outdoors) | Jul 11–Aug 1 (transplant) |
| Spinach | – | May 7–28 (sow outdoors) | Jul 11–Aug 1 (sowing) |
| Kale | Apr 23–May 7 | May 21–Jun 4 (transplant) May 21–Jun 4 (sow outdoors) | Jun 13–Jul 11 (transplant) |
| Collards | Apr 23–May 7 | May 21–Jun 18 (transplant) May 21–Jun 18 (sow outdoors) | – |
| Broccoli | Apr 9–23 | May 21–Jun 4 (transplant) | – |
| Cabbage | Apr 9–23 | May 21–Jun 4 (transplant) | – |
| Cauliflower | Apr 9–23 | Jun 4–18 (transplant) | – |
| Brussels sprouts | Mar 26–Apr 9 | May 21–Jun 4 (transplant) | – |
| Kohlrabi | Apr 23–May 7 | May 21–Jun 4 (transplant) May 21–Jun 4 (sow outdoors) | Jun 27–Jul 11 (sowing) |
| Bok choy / Asian greens | – | May 21–Jun 4 (sow outdoors) | Jul 11–25 (sowing) |
| Arugula | – | May 21–Jun 18 (sow outdoors) | Jul 11–Aug 8 (sowing) |
| Mustard greens | – | May 21–Jun 11 (sow outdoors) | Jul 11–25 (sowing) |
| Swiss chard | May 7–21 | Jun 4–25 (transplant) Jun 4–Jul 2 (sow outdoors) | – |
| Beet | – | May 21–Jun 18 (sow outdoors) | Jun 27–Jul 11 (sowing) |
| Carrot | – | May 28–Jun 25 (sow outdoors) | – |
| Radish | – | May 14–Jun 25 (sow outdoors) | Jul 25–Aug 8 (sowing) |
| Turnip | – | May 21–Jun 11 (sow outdoors) | Jun 27–Jul 11 (sowing) |
| Parsnip | – | May 28–Jun 18 (sow outdoors) | – |
| Pea (garden, snap, snow) | – | Apr 23–May 21 (sow outdoors) | Jun 13–27 (sowing) |
| Onion (bulbing) | Mar 26–Apr 9 | May 7–21 (transplant) | – |
| Green onion / scallion | – | May 7–Jun 4 (sow outdoors) | Jun 27–Jul 11 (sowing) |
| Leek | Mar 26–Apr 9 | May 21–Jun 4 (transplant) | – |
| Garlic | – | – | Jul 25–Aug 22 (sowing) |
| Shallot | – | May 7–21 (transplant) | Jul 25–Aug 22 (sowing) |
| Potato | – | May 21–Jun 4 (transplant) | – |
| Sweet potato | – | Jul 9–23 (transplant) | – |
| Sweet corn | – | Jun 25–Jul 9 (sow outdoors) | – |
| Bean, bush (snap) | – | Jun 25–Jul 9 (sow outdoors) | – |
| Bean, pole | – | Jun 25–Jul 9 (sow outdoors) | – |
| Lima bean | – | Jul 2–16 (sow outdoors) | – |
| Southern pea (cowpea, black-eyed pea) | – | Jul 9–30 (sow outdoors) | – |
| Cucumber | May 21–28 | Jun 25–Jul 9 (transplant) Jun 25–Jul 9 (sow outdoors) | – |
| Summer squash / zucchini | May 21–28 | Jun 25–Jul 9 (transplant) Jun 25–Jul 9 (sow outdoors) | – |
| Winter squash | May 21–28 | Jun 25–Jul 9 (transplant) Jun 25–Jul 9 (sow outdoors) | – |
| Pumpkin | – | Jun 25–Jul 9 (sow outdoors) | – |
| Watermelon | May 21–28 | Jul 2–16 (transplant) Jul 2–16 (sow outdoors) | – |
| Cantaloupe / muskmelon | May 21–28 | Jul 2–16 (transplant) Jul 2–16 (sow outdoors) | – |
| Okra | May 7–21 | Jul 2–16 (transplant) Jul 2–16 (sow outdoors) | – |
| Celery | Mar 26–Apr 9 | Jun 25–Jul 2 (transplant) | – |
| Basil | May 7–21 | Jun 25–Jul 9 (transplant) Jun 25–Jul 9 (sow outdoors) | – |
| Cilantro | – | Jun 4–Jul 2 (sow outdoors) | Jul 11–25 (sowing) |
| Parsley | Apr 9–23 | Jun 4–18 (transplant) May 28–Jun 18 (sow outdoors) | – |
| Dill | – | Jun 18–Jul 2 (sow outdoors) | Jul 11–25 (sowing) |
| Sunflower | – | Jun 18–Jul 2 (sow outdoors) | – |
| Asparagus (crowns) | – | May 21–Jun 4 (transplant) | – |
| Rhubarb (crowns) | – | May 21–Jun 4 (transplant) | – |
| Strawberry (plants) | – | May 21–Jun 4 (transplant) | Jun 27–Jul 25 (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: Tizer Gardens, MT (NOAA GHCN-Daily ID USC00248239), elevation 4,672 ft, 1.1 miles from the ZIP's center point. NOAA completeness flag: R (representative, 10+ years).
Nearby stations
| Station | Distance | Last frost (50%) | First frost (50%) |
|---|---|---|---|
| Boulder, MT | 10 mi | Jun 7 | Sep 8 |
| Helena Rgnl AP, MT | 17 mi | May 9 | Sep 30 |
| Austin 1 W, MT | 23 mi | Jun 4 | Sep 14 |
The average last-frost dates of these stations span 40 days, a rough guide to local variation. See data sources & methods.
Frost questions for 59638
When is the last frost in 59638?
The average (50% chance) last spring freeze of 32°F for ZIP 59638 is June 18. For a more cautious planting date, use July 3, when only 1 year in 10 still sees a later freeze.
When is the first frost in 59638?
The average first fall freeze is September 5. In 1 year in 10 it comes by August 21.
What hardiness zone is 59638?
ZIP 59638 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 59638 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
59634 Clancy 59632 Elkhorn 59601 Helena 59623 Helena 59625 Helena 59635 Spokane Creek 59631 Basin 59636 Helena West Side
Other ZIP codes in Jefferson County
59631 59632 59634 59721 59759 All Jefferson 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
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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.