Montana planting calendar

When to plant brussels sprouts in Montana — sow, transplant & harvest dates

Montana is mostly USDA zone 4b (range 3a-6a). Dates below are derived from brussels sprouts's frost tolerance and Montana's frost window — not generic national averages.

Brussels Sprouts planting timetable for Montana

Stage	When in Montana	Anchor
Start seeds indoors	early March (March 2)	12 weeks before the last frost (late May)
Transplant outside	mid-May (May 11)	14 days before the last frost (late May)
First harvest (estimate)	early August (August 9)	~90 days from transplant

Dates are state-wide averages for the dominant zone. Local microclimates — elevation, urban heat, coastal moderation — can shift the window by 1-2 weeks. Use the frost-date calculator for a date tuned to your town.

Why Montana's climate shifts the brussels sprouts dates

Montana's last spring frost averages late May and first fall frost mid-September, which sets the whole planting clock. Montana is a cold, short-season state with big elevation effects. Western valleys are milder than the high plains and mountain basins. Sow early — brussels sprouts bolt once daytime temperatures hold above 24 °C, so the earlier they go in, the longer the harvest.

Brussels sprouts are a long-season crop — transplant outdoors 2–3 weeks before the last spring frost once seedlings are 10–15 cm tall, or start a fall crop by counting back 90–100 days from the first fall frost and setting transplants then. Flavour sweetens after the first hard frost (below -2 °C), making them one of the few vegetables that actually improves with autumn cold. Zones 9–10 can grow them as a winter crop but the lack of hard frost reduces flavour development.

Frost-risk note

Don't plant before late May — a hard freeze can still set young plants back. In the high mountain valleys and northern plains (zone 3a) the safe date runs a week or two later.

Regional variation within Montana

the high mountain valleys and northern plains (zone 3a) runs roughly 1-2 weeks behind the state average; the lower western valleys near Missoula (zone 6a) can plant 1-2 weeks earlier.

Billings — USDA zone 5a
Missoula — USDA zone 5b
Bozeman — USDA zone 5a
Great Falls — USDA zone 4b
Kalispell — USDA zone 5a

What else to plant in Montana around then

The same early window suits peas, lettuce, spinach, and onion sets.

Quick-grow guide

Sun: Full sun — 6+ hours direct.
Soil temperature for germination: 7-29 °C (45-85 °F).
Spacing: 18-24 inches (45-60 cm) between plants.
Days to harvest: ~90 days from planting out.

Frequently asked questions

When is the best time to plant brussels sprouts in Montana?

In Montana (mostly USDA zone 4b), sow brussels sprouts indoors around early March, transplant outdoors mid-May (before the last frost, late May), and harvest from early August. Brussels Sprouts are cold-hardy — they tolerate frost and actively prefer cool weather, so they go in well before the last spring frost and bolt in summer heat.

What USDA zone is Montana?

Most of Montana sits in USDA hardiness zone 4b, with the state spanning roughly 3a-6a from the high mountain valleys and northern plains (zone 3a) to the lower western valleys near Missoula (zone 6a). The last spring frost averages late May and the first fall frost mid-September.

Can you grow brussels sprouts in Montana?

Yes. Montana's dominant zone 4b supports brussels sprouts — the key is timing. Brussels Sprouts are cold-hardy — they tolerate frost and actively prefer cool weather, so they go in well before the last spring frost and bolt in summer heat.

Does the planting date change across Montana?

the high mountain valleys and northern plains (zone 3a) runs roughly 1-2 weeks behind the state average; the lower western valleys near Missoula (zone 6a) can plant 1-2 weeks earlier.

What else can I plant in Montana around the same time?

The same early window suits peas, lettuce, spinach, and onion sets.

Source and methodology

State zone spans from the USDA Plant Hardiness Zone Map (2023); frost-date averages from NOAA Climate Data Online. Hot-state two-season timing cross-checked against the UF/IFAS Florida Gardening Calendar and the University of Arizona Cooperative Extension planting calendar. Curated by the Growli editorial team.