Lewistown, MT 59489 Frost Dates
When can you plant in Lewistown, MT?
The last spring frost here typically falls around 05/14, about 259 days from today. The first fall frost typically arrives around 09/28, about 135 frost-free days later.
Zone 4b (-25 to -20°F average annual minimum) comes from the USDA Plant Hardiness Zone Map; the frost dates above are the 1991-2020 normal at the nearest reporting NOAA station for Lewistown, not a forecast for this year.
What to do before the first frost
About 4 weeks of growing season left in Lewistown before the first fall frost — a cold frame or row cover can stretch harvest weeks past that date.
Why 05/14 isn't a guarantee
05/14 is the middle of 30 years of NOAA records, not a promise. Plant by 05/02 and you're betting against frost in roughly 9 years out of 10. 05/27 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Lewistown compares
Lewistown's growing season runs about 135 days, ranking 37,845 of 40,283 US ZIP codes measured here, longest to shortest. Within MT, it ranks 95 of 392.
Learn more
local microclimates covers what one yard in Lewistown can differ from the 59489 normal. zone vs. frost date covers why Zone 4b and Lewistown's frost date answer different questions.