USDA Hardiness Zone 4a
Frost Dates for 59538 — Malta, Montana
NOAA 1991–2020 normals from Malta, MT (2,262 ft), 9 miles north.
Updated
In Malta, the last spring frost (32°F) is around May 10 in half of years and has passed by May 22 in nine years out of ten. The first fall frost comes around September 29, as early as September 17 one year in ten, leaving a typical freeze-free season of 139 days (NOAA, Malta, MT).
- Last spring frost
- May 10
- First fall frost
- September 29
- Growing season
- 139 days
- Hardiness zone
- 4a
50% probability
50% probability
freeze-free, 50%
-30 to -25°F (-34.4 to -31.7°C) coldest night
- First snow
- November 17
- Last snow
- March 2
- Winters with snow
- 96%
- Snow per year
- —
median, 1991–2020
median, 1991–2020
23 of 24 observed
NOAA normal
Frost risk by date in Malta
Half of springs at Malta, MT see their last 32°F night by May 10; only one in ten is past it by April 29, and one in ten still has one after May 22. Planting tender crops after May 14 leaves a 30% risk of a frost on them, after May 17 20%, and after May 22 10%. The 12 days between the even-odds date and the one-in-ten date is the narrowest of the 68 Montana stations behind this site's ZIP pages.
In fall the first 32°F night comes by September 29 in half of years, as early as September 17 one year in ten, and holds off past October 10 one year in ten. A hard freeze of 28°F follows 7 days later, around October 6; in spring the one-in-ten date for 28°F is May 12, 10 days before the 32°F one. The freeze-free season lasts 139 days in a typical year, longer than at 75% of the 68 Montana stations; it reaches 157 days one year in ten and falls short of 123 one year in ten. On average 173 nights a year drop to 32°F or below. Nights of 36°F, when frost can still settle on leaves in low, open spots, continue 9 days longer, to about May 19, and return around September 20. Severe cold of 16°F or below comes every winter, usually between November 2 and March 28.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 8 | May 12 | May 15 | May 17 | May 19 | May 22 | May 24 | May 27 | May 31 |
| 32°F | Apr 29 | May 2 | May 5 | May 8 | May 10 | May 12 | May 14 | May 17 | May 22 |
| 28°F | Apr 13 | Apr 18 | Apr 22 | Apr 27 | Apr 30 | May 1 | May 4 | May 7 | May 12 |
| 24°F | Apr 1 | Apr 6 | Apr 10 | Apr 12 | Apr 16 | Apr 20 | Apr 23 | Apr 27 | May 1 |
| 20°F | Mar 17 | Mar 24 | Mar 31 | Apr 2 | Apr 5 | Apr 8 | Apr 12 | Apr 16 | Apr 21 |
| 16°F | Mar 10 | Mar 15 | Mar 19 | Mar 24 | Mar 28 | Mar 31 | Apr 3 | Apr 7 | Apr 13 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 6 | Sep 12 | Sep 16 | Sep 18 | Sep 20 | Sep 22 | Sep 24 | Sep 27 | Sep 30 |
| 32°F | Sep 17 | Sep 21 | Sep 24 | Sep 26 | Sep 29 | Oct 1 | Oct 3 | Oct 6 | Oct 10 |
| 28°F | Sep 23 | Sep 28 | Oct 1 | Oct 3 | Oct 6 | Oct 9 | Oct 12 | Oct 15 | Oct 19 |
| 24°F | Sep 29 | Oct 4 | Oct 9 | Oct 12 | Oct 15 | Oct 18 | Oct 21 | Oct 25 | Oct 30 |
| 20°F | Oct 9 | Oct 14 | Oct 18 | Oct 21 | Oct 25 | Oct 28 | Oct 31 | Nov 3 | Nov 7 |
| 16°F | Oct 18 | Oct 24 | Oct 29 | Oct 31 | Nov 2 | Nov 5 | Nov 8 | Nov 12 | Nov 18 |
Freeze probabilities 1991–2020 at Malta, MT, from NOAA NCEI U.S. Climate Normals. Where a temperature is reached in fewer than 99.5% of years, the dates describe only the years that reach it. Not a forecast.
Frost risk on any date in 59538 →Compare Malta with another place →
Weather by month in Malta
July is the warmest month at Malta, MT, averaging 86°F by day and 57°F at night; January is the coldest at 29°F and 7°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). From June to August the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 86% of years.
Warmth for growing adds up to 2,412 growing degree days a year (base 50°F), more than at 88% of the 68 Montana stations. 29% of them (702) have built up by the end of June, and July adds the most, 677. Precipitation totals 13.5 inches a year, most in June (2.7") and least in January (0.4"); May to September bring 64% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 29 | 7 | 0.4 | 100% | 30 | 0 |
| Feb | 32 | 11 | 0.4 | 100% | 27 | 0 |
| Mar | 45 | 21 | 0.5 | 100% | 27 | 7 |
| Apr | 59 | 33 | 1.3 | 100% | 14 | 53 |
| May | 69 | 42 | 1.7 | 86% | 3 | 211 |
| Jun | 77 | 52 | 2.7 | 0% | 0 | 432 |
| Jul | 86 | 57 | 1.6 | 0% | 0 | 677 |
| Aug | 86 | 56 | 1.3 | 0% | 0 | 640 |
| Sep | 74 | 46 | 1.4 | 58% | 1 | 316 |
| Oct | 59 | 33 | 1.0 | 100% | 14 | 71 |
| Nov | 43 | 20 | 0.7 | 100% | 26 | 6 |
| Dec | 31 | 10 | 0.5 | 100% | 31 | 0 |
Monthly normals 1991–2020 at Malta, MT (2,262 ft), NOAA NCEI. "32°F night": chance of at least one in the month. GDD: growing degree days, base 50°F.
When it snows in Malta, Montana
The first measurable snow (0.1 inch or more) in Malta usually arrives around November 17, and the last of the season around March 2. Those are the middle dates across the winters of 1991–2020 at Malta, MT, 9 miles away: half of years saw snow earlier, half later. Snow fell in 96% of those winters. The last 32°F night of spring typically comes 69 days after the last snow.
Planting calendar for 59538
| When | What to do |
|---|---|
| March 1 – March 15 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 15 – March 29 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 12 – April 26 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 10 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 7 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 15 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| September 29 onward | Plant garlic, mulch beds, lift tender bulbsGarlic wants a cold spell; bare soil loses structure over winter. |
The weeks before and after the 50% dates are general rules of thumb, not NOAA figures; a seed packet gives the timing for each variety.
Where these figures come from
ZIP 59538 is 9 miles from Malta, MT, which stands at 2,262 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 59538 in zone 4a, the band where the coldest night of the year averaged -30 to -25°F (-34.4 to -31.7°C) over 1991–2020; a zone describes winter lows, not frost dates.
Hardiness zone and temperature range: USDA Plant Hardiness Zone Map 2023 (USDA-ARS, Oregon State University), ZIP-code listing, unchanged. °C converted from °F by this site.
Thirty-year averages, not a forecast: check the forecast before planting out. How stations are matched and which pages are offered to search engines: methodology.