USDA Hardiness Zone 5b
Frost Dates for 59804 — Missoula, Montana
Averages from Missoula Intl Ap, Mt US, the nearest reporting station, 4.6 miles away.
Plant tender crops after May 16, and expect the first autumn freeze around September 26. That leaves about 130 frost-free days.
- Last spring frost
- May 16
- First fall frost
- September 26
- Growing season
- 130 days
- Hardiness zone
- 5b
50% probability
50% probability
frost-free
-15 to -10°F annual low
Planting calendar for 59804
| When | What to do |
|---|---|
| March 7 – March 21 | Start peppers and aubergines indoors They need eight to ten weeks under lights before they can go out. |
| March 21 – April 4 | Start tomatoes indoors Six to eight weeks gives a transplant big enough to set fruit early. |
| April 18 – May 2 | Sow peas, spinach, lettuce, radish outdoors These tolerate light frost and prefer to germinate in cool soil. |
| May 16 onward | Transplant tomatoes, peppers, basil, squash, cucumbers The average last freeze has passed — still watch the actual forecast. |
| by July 4 | Sow the autumn crop of carrots, beets and brassicas They need about twelve weeks to size up before growth stops. |
| by September 12 | Harvest tender crops, or be ready to cover them A first freeze two weeks early is well within normal variation. |
| September 26 onward | Plant garlic, mulch beds, lift tender bulbs Garlic wants a cold spell; bare soil loses structure over winter. |
What these dates mean
Wait until after May 16 to put tender plants — tomatoes, peppers, basil, squash — in the ground. That is the date by which half of years in Missoula, Montana are past their last freeze. Harvest before September 26, which leaves roughly 130 frost-free days.
ZIP 59804 sits in USDA hardiness zone 5b, meaning the average coldest night of the year falls between -15 to -10°F. Zone decides what survives the winter; frost dates decide when to plant each spring. They are different questions, and a plant can pass one and fail the other.
These are thirty-year NOAA averages for 1991–2020, not a forecast. Any individual year can frost two to three weeks either side of these dates, so check the actual forecast before planting out.