USDA Zone 4b — Garden & Frost Dates for Helena, MT (59601)
This is the local garden report for ZIP code 59601 (Helena, MT). It pairs the official USDA 2023 hardiness zone with NOAA-based frost dates so you can plan seeds, transplants, and fall crops with real numbers for your neighborhood.
What does zone 4b mean for Helena?
Zone 4b is the USDA Plant Hardiness Zone for ZIP 59601, based on the 30-year (1991-2020) average annual extreme minimum winter temperature. Perennial plants labeled for zone 4b or lower should survive a typical winter here. The last spring frost averages 05-15 and the first fall frost averages 09-18, giving roughly 126 frost-free growing days — the window that most vegetables need to go from seed to harvest.
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