When to Plant in Montana: A Month-by-Month Guide for a Short Season

You have roughly 90 to 160 frost-free days, depending on which valley you live in. One late-May frost can erase six weeks of work you did indoors under a shop light.

That frustration is real. It is also not a mystery. The season here is short, and it is knowable: your frost-free window is mapped, the cultivars that fit inside it have been bred and tested, and the difference between a busted year and a full pantry comes down to two numbers you can look up this afternoon.

What follows is a genuine month-by-month calendar, March through October, with what to sow, what to transplant, what to prune, and what to leave alone. Every date assumes an average valley-bottom year at roughly 4,000 feet, though your dates will move, and the section right below tells you which way they move.

The two numbers that decide everything

Nothing else on this page matters until you know your zone and your frost-free days, because everything else is arithmetic on top of those two figures.

Montana spans zones 3a through 6b on the 2023 USDA map, the first update since 2012, and one that moved most Montana cities roughly half a zone warmer, which means that if you're working from an older zone number, you're working from a stale one.

The state's frost-free window runs from about 90 days at the highest valley towns up to roughly 160 on the warmest eastern plains. Red Lodge and Butte sit at the short end, while Glendive sits at the long end. For the full city-by-city table, see Montana frost dates by city, which carries the station-level numbers and the last-frost and first-frost dates for each place.

Two caveats before you use any of those figures. First, frost-free counts are single-station estimates, and they vary within a city, sometimes street by street, so two gardens a mile apart can be working from two different seasons. Second, published frost dates are usually stated at the 50% probability level, which means that in half of all years, the last spring frost arrives after the date on the chart. Read that last part twice. A date on a chart is not a promise; it is a coin flip that someone wrote down. Verification is free at the official USDA tool, planthardiness.ars.usda.gov, and you should check it rather than trust any table. For a closer look at the mechanics, see how Montana frost dates actually work.

Elevation is the master variable, not latitude. Red Lodge sits at 5,562 feet and Butte at 5,539, and those are the shortest seasons in the state. Polson sits at 2,930 feet and Havre at 2,493, and both are among the longest. Moving 1,000 feet up the hill can cost you two or three weeks on both ends, and latitude barely registers by comparison.

That is also why your zone matters more than the calendar does, and why a date copied out of a national magazine so rarely survives the trip out here. A generic "plant in May" instruction written for Billings will wipe out a garden in Butte. If you haven't pinned your zone down yet, the Montana growing zones explainer walks through the map and the microclimates that override it.

Microclimates: where the calendar lies to you

Within a single valley, your exact spot can run a zone or more off the city average.

• South-facing slopes warm earlier, melt snow earlier, and ripen fruit better; that is the classic orchard site, for good reason.
• Valley cold-air pooling is the counterintuitive one. Cold air drains downhill and pools on valley floors, so the bottom of the valley is often colder at night than the slope just above it. Missoula is a textbook inversion valley. The practical rule: put your frost-sensitive plants partway up a slope, never in the bottom.
• Thermal belts, the mid-slope band above the inversion layer, stay warmer all winter; that's where Montana's historic orchards were sited.
• Lakeshore moderation is dramatic on Flathead. Shoreline communities from Polson to Lakeside, Big Arm, Finley Point and Rollins run zone 5b–6b, and Big Arm, Finley Point and Belknap reach 6b, the warmest classifications recorded in the state. Polson also has the latest average first fall frost of the major cities.
• Urban heat runs a city warmer than the surrounding plain.
• Windbreaks cut wind, reduce winter water loss, trap snow, and raise soil temperature, and if you're on open ground, a shelterbelt changes your planting calendar.

The frost tiers: what survives what

Before the calendar, the tiers. These govern every "can I set this out yet" decision you will make this year.

The tier is what tells you when the clock starts, because a very tender crop doesn't begin accumulating useful growth until nights are reliably above 40°F, which in most Montana valleys means early to mid-June, not the first of May. That gap between your nominal frost-free count and your effective growing window is where most Montana gardens are lost.

How to set your planting date

Four steps, in order; do them once and you have a date you can defend instead of a guess from a seed packet.

1. Find your frost-free days. Look up your city or the nearest reporting station in the Montana frost dates by city table, or verify against the USDA tool at planthardiness.ars.usda.gov, and that count is the length of your whole season.
2. Estimate your last-frost date. Take the published last-spring-frost date for your station, and remember it sits at the 50% probability level, so half of all years frost later than that date.
3. Add a one-week buffer for tender crops. Tomatoes, peppers, cucumbers, squash and corn go out a week after the published date, not on it. Very tender crops, meaning eggplant, melon and pumpkin, want nights above 40°F, which is later still, though hardy crops need no buffer at all.
4. Adjust for elevation. Add roughly two to three weeks to both ends for every 1,000 feet above your reference city. Red Lodge and Butte, both around 5,500 feet, run shortest; low towns like Polson and Havre run longest.

The calendar

All of this assumes a valley-bottom site around 4,000 feet in a 4b–5b zone. Go up in elevation and shift everything later in spring and earlier in fall.

March: indoors, and pruning that pays

Sow: Indoors only. Start peppers and eggplant, if you intend to fight for them, 8–10 weeks before your last frost, plus onions and leeks from seed, and celery. Set up your lights now, because the season you're buying back is the one you grow on a shelf.

Transplant: Nothing outdoors, since the ground is still frozen or barely thawed.

Prune: Late dormant pruning is the best pruning of the year, because deciduous trees and shrubs are dormant and their structure is visible. This is also the correct window for firewise limbing, taking trees up to 6–8 feet so ladder fuels can't carry fire into the canopy. That work belongs in your defensible-space plan, and doing it in March means it's finished before fire season.

Not yet: Don't prune spring-flowering shrubs. Lilac, forsythia and their relatives set this year's buds last summer, so pruning them now cuts off the bloom; wait until right after they flower. Don't till wet soil; you'll make brick, and don't fertilize a lawn that isn't growing yet.

April: the ground opens

Sow: Indoors, start your tomatoes 6–8 weeks before last frost and your brassicas on a similar clock. Outdoors, if the ground is workable late in the month, direct-sow the hardy tier: peas, spinach, lettuce, kale, radishes.

Transplant: Harden off hardy crops and move them into cold frames or low tunnels late in the month. Harden transplants over 7–14 days. MSU Extension is explicit about this, and skipping it is the single most common way a healthy seedling dies during its first week outside.

Prune: Finish dormant pruning early in the month, before buds break. Prune nothing else.

Not yet: Don't set out anything half-hardy or tender. Don't plant trees or shrubs yet, since that window belongs to the fall, and don't schedule an installation. Ground in most Montana valleys doesn't thaw until late April, and hardscape work booked before it does just means crews standing around.

May: the half-hardy month

Sow: Direct-sow the half-hardy tier, meaning beets, carrots, chard, onion sets and radish, set out broccoli, cabbage and cauliflower transplants, and keep succession-sowing lettuce and spinach every two weeks.

Transplant: Harden off and set out half-hardy crops under protection. This is the month Montana's planting window genuinely opens for everything except the tender crops.

Prune: Prune spring-flowering shrubs after they finish blooming. That's the whole rule.

Not yet: Don't set out tomatoes, peppers, cucumbers, squash or corn. Remember what the 50% probability level means: in half of years, your last frost lands after the chart date. Mid-May through June is the optimal planting window statewide, and it's also the most contested booking period of the year. If you want a crew, this is the month everyone else wants them too.

June: the main event

Sow: Succession-sow lettuce, radish and spinach every two weeks, because they bolt fast in heat, and direct-sow beans and corn once the soil has settled warm.

Transplant: This is the month for tomatoes, peppers, squash, cucumbers and corn, but wait until the soil has warmed and nights are settled. A rule of thumb is that these crops want soil meaningfully warmer than the hardy tier, and a cold snap behind a June transplant sets them back further than waiting another week would have. Harden everything off first. Plant your tomatoes deeper than they sat in the pot; they'll root along the buried stem.

Prune: Prune any spring bloomers that have finished, and pinch tomato suckers if you're growing indeterminate varieties on a trellis.

Not yet: Don't gamble on the calendar alone. On the eastern and central plains, where hail frequency is also highest, a June cold snap behind a warm spell is entirely normal, and a tomato set out early because the chart said the risk had passed can sit in cold ground for two weeks without adding a single inch, sulking, while the weeds around it put on weight. And if you're in Bozeman or Missoula, understand that June and July are peak season with 4–8 week lead times; the planting advice and the scheduling advice are the same advice.

July: the fall garden starts now

Sow: This is the month most Montana gardeners miss. Mid-to-late July is when you sow the fall harvest, meaning kale, lettuce, spinach, carrots, beets, radish and broccolini, because the crops mature into cooling weather instead of into August heat.

Transplant: Nothing new and tender; keep the succession going.

Prune: Deadhead flowers to keep them producing, and don't hard-prune anything now, since you're stressing the plant at the hottest, driest point of its year.

Not yet: Don't plant woody stock, and don't fertilize in a way that pushes soft, late growth.

August: stop pruning wood

Sow: Finish your fall-garden succession in the first half of the month, since spinach sown now can overwinter in a mild valley. Late August opens the grass-seeding window, which gets its own section below.

Transplant: Nothing new and tender.

Prune: Stop. No pruning of woody plants from here on. Pruning stimulates new growth, and new growth in August and September doesn't have time to harden off before the first freeze. So it dies, and it drags the plant's winter hardiness down with it. This is the mechanism behind a lot of the damage described in why evergreens turn brown in winter.

Not yet: Don't plant trees or shrubs late, and remember that wildfire smoke can also halt outdoor work entirely in August, so build slack into any project you schedule this month.

September: trees and garlic prep

Sow: Little to sow now, so hold garlic until the very end of the month or October.

Transplant: September is the best month of the year for tree transplants in Montana. Soil is still warm, air is cooling, and roots keep growing long after the top growth stops, which is exactly the condition a transplant needs. Hardy nursery stock planted now establishes far better than anything planted in spring. Choose species that will actually survive here in the first place with the best trees for Montana guide. Note the distinction that trips people up. This is a hardy nursery stock window, not a license to plant late-season tender material. The "don't plant late" rule is about plants that can't harden off in time, and a hardy tree going in during September is doing the opposite.

Prune: Remove dead, diseased or broken wood only, with no structural pruning, no thinning, no "shaping."

Not yet: Don't fertilize woody plants, and don't plant anything that hasn't hardened off.

October: garlic, native seed, and water

Sow: Garlic goes in the ground in fall, and the rule of thumb is to plant roughly four to six weeks before the ground freezes, which in most Montana valleys is late September through mid-October, earlier as you go up in elevation. The goal is roots without tops: the clove roots in, but the shoot doesn't emerge before winter, so mulch it heavily after the ground freezes. October is also the right window for late-fall seeding of native forbs and grasses, since many of them need cold stratification to germinate, and MSU Extension's native-plants guidance names late-fall seeding as optimal. If that's your plan, the native plants of Montana guide covers sourcing and establishment, and warns you never to wild-dig.

Transplant: Finish any tree and shrub planting by mid-October if you can.

Prune: Nothing.

Not yet: Don't skip irrigation winterization. It's mandatory and scheduled in early October; missing the window costs $500–$2,000 in repairs once a line splits. Don't over-fertilize turf going into dormancy, which is a direct feed into spring snow mold. And don't let the yard go into winter dry, because deep fall watering until the ground freezes is the highest-value hour you'll spend on the landscape all year.

The rule that tells you what you can't grow

The whole thing fits in one sentence: if a plant's days-to-maturity exceeds your frost-free days, and the plant has no frost tolerance, you cannot grow it outdoors without protection.

Days-to-maturity typically counts from transplant, not from seed, and that distinction trips people. Run the test against a Montana-length season and three popular crops fail it:

• Eggplant (100–120 days)
• Melons (80–100 days)
• Pumpkin (100–120 days)

All three are very tender, damaged below 40°F, so their clock doesn't start until nights are reliably warm, which in most Montana valleys is mid-June. Count forward from mid-June and the arithmetic runs out before the first fall frost. Against a Bozeman-length season, these are high-tunnel crops, not garden crops. That's not defeatism; it's the difference between spending a summer losing and spending a summer harvesting.

What to grow instead

MSU Extension publishes a tested list of tomato cultivars for short seasons: Bloody Butcher, Early Girl, Early Pick, Fourth of July, Gem State, Northern Exposure, Oregon Spring, Prairie Fire, Siberian, Stupice and Sub Arctic Plenty. For small-fruited types, faster to ripen and more forgiving of a cool August: Gold Nugget, Juliet, Sungold, Super Sweet 100 and Yellow Pear.

For containers and greenhouses, MSU Extension MontGuide MT199308AG names: bean Contender, Provider, Tendercrop · carrot Short 'n' Sweet, Gold Nugget · cucumber Burpless Early Pik · lettuce Arctic King, North Pole · pea Little Marvel, Laxton's Progress · pepper Gypsy Hybrid, Canape · radish Cherry Belle, French Breakfast · squash Butterbush · watermelon Sugar Baby.

Those cultivar names are not marketing copy; they're the result of a land-grant institution testing what actually ripens here.

Season extension: buying back four weeks

If you want eggplant, melons or a real tomato harvest on the Hi-Line, you extend the season rather than fight it.

Low tunnels are the standard tool. Build them over ½-inch conduit hoops with spun-poly covers rated to 4°F of protection. That single layer of fabric moves your effective season by weeks on both ends and costs a fraction of a permanent structure, so harden transplants into them over 7–14 days.

Row cover selection matters more than people expect, and so does mulch color. In Bozeman trials, red plastic mulch sped tomato warming and ripening, and black plastic mulch did not significantly raise soil temperature. That result is counterintuitive enough that it's worth repeating: the black plastic everyone reaches for first isn't doing the job people think it's doing. If you're buying mulch to warm soil, buy red.

Season-extension materials are cheap. Labor isn't. If you'd rather have the tunnels built than build them, the Montana landscaping cost guide gives you real numbers with the state's labor premium explained.

When to plant grass seed in Montana

This is one of the most-searched planting questions in the state, and the answer is genuinely different from the vegetable calendar.

The best window is late summer into early fall, roughly mid-August through mid-September in valley locations, earlier at elevation. Cool-season grasses establish best then because the soil is still warm, the air is cooling, and weed competition is winding down. Seeded turf gets months of root growth before winter instead of three weeks.

Spring seeding works, but it's the harder path. You're racing summer heat and peak weed pressure with a seedling root system, so if you must seed in spring, do it as early as the ground can be worked and plan to irrigate through July.

Two rules that decide whether it takes. First, keep the seedbed consistently moist, not soaked, until germination and through the first mowings. Second, don't over-fertilize in fall; pushing lush growth into winter is a direct invitation to gray snow mold, which MSU Extension notes shows up on Montana lawns most springs. Prevention is cultural, not chemical. MSU states plainly that fungicides are "not usually recommended for home lawn use." Mow until dormancy, don't pile snow on turf, and fix drainage. If your lawn comes out of winter yellow for other reasons, that's a different diagnosis.

Dormant seeding, sowing so the seed sits until spring, is a legitimate option on the eastern plains where reliable snow cover protects the seedbed, though it's a gamble in a valley with open, windy winters.

When to plant potatoes in Montana

Potatoes are the exception to almost everything above, and that's why they're worth their own answer. They are a hardy crop, so they tolerate a hard freeze, and they go in the ground before your last frost, not after it.

The window is late April to mid-May in most Montana valleys. The trigger isn't a date on the calendar, it's the ground, so plant when the soil is workable, meaning thawed and no longer clumping, at a soil temperature around 45°F. In a typical valley-bottom year that lands late April into the first half of May. Two adjustments, and they run in opposite directions:

• Earlier on the eastern plains. The lower, drier country east of the divide, around Sidney, Glendive and Miles City, warms sooner and can be planted up to a couple of weeks ahead of the western valleys.
• Later at elevation. In Butte, Red Lodge and the higher mountain valleys, workable ground may not arrive until late May or early June, so use your own elevation rather than a statewide date.

Seed potatoes, meaning certified seed rather than grocery-store spuds, which carry disease and may be treated with sprout inhibitors, are chitted, or pre-sprouted, indoors in a cool, bright spot for two to four weeks before planting. Set them out cut-side down, eyes up, about four inches deep and twelve inches apart, and hill soil around the stems as they grow. Potatoes also tolerate a light frost on the foliage once up, though a hard freeze will blacken the tops; they usually regrow from below.

Because they go in early and come out early, potatoes are the crop that lets you follow with a second planting, and the mid-to-late July fall-garden window in the calendar above is exactly what a harvested potato bed is for.

Where new plants go, and what will eat them

One last thing before you plant anything: figure out what's already browsing your yard.

Deer browse reaches about 6 feet, and MSU Extension's deer-damage guidance is unambiguous that no plant is safe from a hungry deer. "Deer-resistant" does not mean "deer-proof." New transplants are the most vulnerable thing on the property, and a seedling nibbled to the ground in June costs you the whole season. Choosing species with better resistance is the first line of defense. The deer-resistant plants guide ranks them, and it explains how to tell deer browse from rabbit damage: deer lack upper incisors, so their browse is torn and jagged, while a rabbit leaves a clean 45° cut.

If you're planting in the Flathead, in the Gallatin, or anywhere else with real hunting and wildlife pressure, plan the nursery order around it rather than replanting twice.

Frequently asked questions

When can I plant tomatoes in Montana?

Not before your last frost, which for most Montana valleys falls in the second half of May, and remember that published dates sit at the 50% probability level, so half of all years frost later. Harden the transplants off over 7–14 days first, then set them out around the turn of June and choose a short-season cultivar from MSU Extension's list. In Butte or Red Lodge, add two to three weeks.

Can I plant grass seed in the spring in Montana?

You can, but it's the harder of the two windows. Late August through mid-September is the better bet because the soil is warm and weed pressure is falling. If spring is your only option, seed as early as the ground can be worked and be ready to irrigate through the hot stretch.

When do you plant garlic in Montana?

In fall, roughly four to six weeks before the ground freezes, which lands in late September through mid-October in most valleys and earlier at elevation. Plant it so roots establish but no shoot emerges, then mulch heavily once the ground freezes.

What can I plant before the last frost?

The hardy tier: asparagus, kale, lettuce, pea, potato, rhubarb and spinach. Half-hardy crops, meaning beet, broccoli, cabbage, carrot, cauliflower, chard, onion and radish, can go out under protection a couple of weeks ahead of the frost date. Nothing else.

Does elevation really change my planting dates?

It changes them more than anything else, including latitude. Red Lodge at 5,562 feet and Butte at 5,539 have the shortest seasons in the state; Polson at 2,930 and Havre at 2,493 have some of the longest. Gaining 1,000 feet can cost you two or three weeks on both ends of the season.

The season is short. It isn't random.

The reason Montana gardening feels punishing is that most of the advice in circulation was written somewhere else, for a 180-day season with a gentle frost and an October that behaves. You don't have that, and pretending otherwise is how people lose a year in their first May.

But you do have something better than a long season: a mapped, predictable one, with zones that are documented, frost windows that are published, cultivars that were bred and tested for exactly this length of summer, and a land-grant university that has been publishing Montana-specific guidance since the 1890s.

Respect the two numbers. Read the tier before you set anything out. Plant trees in September and garlic in October. And when a crop fails its days-to-maturity test, believe the arithmetic instead of the seed packet's photograph.

Not sure what will grow where you are? Find your Montana growing region. The region pages carry the local frost windows, the soil conditions, and the plants that actually make it there.