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.
Start your Helena planting calendar
This calendar is pre-loaded with the exact frost dates for ZIP 59601 (Helena, MT) — more precise than a state-wide average. Pick a crop and print the plan.
In this ZIP (typical zone 3–6), last frost ≈ May 15, first frost ≈ Sep 18 (126-day season), your Tomato plan:
Month-by-month (this ZIP, 2026)
| Month | Action |
|---|---|
| Jan | — |
| Feb | — |
| Mar | — |
| Apr | Start indoors |
| May | Sow · Transplant |
| Jun | — |
| Jul | — |
| Aug | Harvest |
| Sep | — |
| Oct | — |
| Nov | — |
| Dec | — |
Start indoors 6 weeks before last frost; transplant after soil warms. Zones 3–13 suitable. Dates are typical; confirm with your county extension and watch the 10-day forecast.
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