USDA hardiness zone lookup
Helena (59601) — USDA Zone 5a
Helena, Montana · 126-day growing season
Frost dates and growing season for 59601
| USDA hardiness zone | Zone 5a |
|---|---|
| Average last spring frost | May 17 |
| Average first fall frost | September 20 |
| Growing season length | ~126 days |
| Temperature range (F) | -20 to -10°F |
| Temperature range (C) | -29 to -23°C |
These are 50%-probability averages modeled from this ZIP's USDA hardiness zone and regional climate normals — not a single-station reading. In a typical year the last spring frost will have passed by May 17, but in a colder-than-average year it can run 1-2 weeks later. Plant tender crops (tomatoes, peppers, basil) once both soil and night temperatures are consistently warm — a thermometer beats the calendar.
Growing season in Helena
Helena, Montana sits in USDA Zone 5a, with roughly 126 frost-free days between an average last spring frost around May 17 and a first fall frost around September 20. That is a standard temperate season — most common vegetables finish comfortably, and a single main planting plus one succession round works well. Helena lies near 46.6°N; higher-latitude gardens get longer midsummer days but a tighter shoulder season at this zone.
What grows in Helena
Helena falls in USDA Zone 5a, which means the same hardiness constraints apply as the full Zone 5 guide. Vegetables, herbs, and fruit trees rated to Zone 5a (or hardier) will overwinter here in a typical year.
- Tomatoes (full range of varieties)
- Peppers
- Eggplant
- Squash, melons, cucumbers
- Beans (bush + pole)
- Sweet corn
- Apples, pears, plums
- Cherries (sweet + sour)
- Blueberries, raspberries
- Garlic
What to plant in Helena this week
Helena's last frost is around May 17. This is the spring transplant window — start tomatoes and peppers indoors if you haven't, and direct-sow cold-tolerant crops now.
- When to plant tomatoes in zone 5
- When to plant peppers in zone 5
- When to plant basil in zone 5
- When to plant bush beans in zone 5
- When to plant cucumbers in zone 5
Full planting calendar for Helena
Crop-by-crop sowing, transplant, and harvest dates calibrated to zone 5 averages:
- When to plant tomatoes in zone 5
- When to plant peppers in zone 5
- When to plant basil in zone 5
- When to plant garlic in zone 5
- When to plant lettuce in zone 5
- When to plant bush beans in zone 5
- When to plant cucumbers in zone 5
- When to plant summer squash in zone 5
- When to plant peas in zone 5
- When to plant carrots in zone 5
Local microclimate notes
Zone tables give you the average — but Helenagardens vary. South-facing walls and paved areas can run a full half-zone warmer than the published rating. Low-lying spots, frost pockets, and shaded north sides can run colder. If you've gardened here a few seasons, your own frost record (the last time you actually got frost damage) is more accurate than any national average.
Source and methodology
Hardiness zone from the USDA Plant Hardiness Zone Map (2023 revision). Frost-date and growing-season figures are modeled from this ZIP's USDA hardiness zone and regional NOAA 1991-2020 climate normals — they are zone-level estimates, not a per-station record, so treat them as planning guidance and confirm against your own local frost history. Crop recommendations are drawn from US Cooperative Extension references and curated by the Growli editorial team. Last reviewed May 2026.
Nearby ZIP codes in Montana
- 59101 — Billings (Zone 5a)
- 59801 — Missoula (Zone 5b)
- 59715 — Bozeman (Zone 4b)
- 59102 — Billings (West) (Zone 5a)
- 59405 — Great Falls (Zone 4b)
- 59901 — Kalispell (Zone 5a)
- 59718 — Bozeman (West) (Zone 4b)
- 59701 — Butte (Zone 4a)
- 59802 — Missoula (East) (Zone 5b)
- 59047 — Livingston (Zone 4b)
- Browse all US ZIP codes by state