One of the hardest parts of gardening in Missoula is knowing when to do what. Our short season leaves little room for error, and seed packets written for the whole country rarely account for how late our spring arrives. A month-by-month schedule built around our actual frost dates takes the guesswork out of it. Here is roughly how the seed-starting year looks for a Missoula garden.
Everything here is anchored to our frost dates. Missoula’s median last spring frost is mid May (about May 16 at the airport, per NOAA’s 1991 to 2020 normals), but in about 1 year in 10 it comes after June 1. The median first fall frost is late September (about September 26), and in about 1 year in 10 it arrives by mid September. Low spots where cold air settles can run later in spring and earlier in fall. Watch the weather each year and adjust, but this gives you a dependable framework, and the Missoula Planting Calendar puts the crop-by-crop dates in one table.
February and March: Start the Slow Crops Indoors
The seed-starting year really begins indoors in late winter. Broccoli and cabbage need about six to eight weeks indoors, so seeds started in late February or early March are ready to set out in April. Peppers are the first of the summer crops, since they are slow to germinate and grow, so start them indoors in late March or early April, about eight weeks before they go out. MSU Extension lists six to eight weeks to transplant size, and slow hot peppers under strong lights can use closer to ten. Onions and leeks from seed also like an early start around this time.
Late March into early April is when tomatoes go in. Tomatoes need about six to eight weeks indoors before transplanting, so starting them in late March to mid-April lines them up to go out after the last frost. Resist the urge to start tomatoes in February. Started too early, they outgrow their pots and turn leggy long before it is safe to plant them out.
April: Cool-Season Crops Go Outside
April is when the outdoor garden wakes up, even though the last frost is still weeks away. Cool-season crops tolerate cold soil and light frost, so you can direct sow them well ahead of it. As soon as the soil can be worked, sow peas, spinach, radishes, lettuce, and other hardy greens directly in the ground. Carrots and beets can go in during April too.
This is also the time to set out hardy transplants, either started indoors or bought as starts. Broccoli and cabbage, after their six to eight weeks indoors, can go out in mid to late April. Cauliflower needs only four to five weeks indoors, so start it in late March and set it out from about late April. Kale is easy to direct sow now or plant from starts. These plants handle the cool weather and get a jump on the season. Keep a row cover handy to throw over tender young plants if a hard freeze threatens.
May: The Big Transition
May is the busiest month and the one that requires the most patience. Early in the month you can keep direct sowing cool-season crops and succession planting more lettuce and greens. But the warm-season crops still have to wait. The exception is indoor starts. Cucumbers and summer squash need only about four weeks indoors, and winter squash three to four, so late April or early May is the time to sow them in peat or paper pots if you want transplants rather than direct sowing.
Once the danger of frost has passed and the soil has warmed, usually from late May into early June after a look at the 10-day forecast, it is finally time for the warm-season crops. Direct sow beans, squash, cucumbers, and corn into warm soil, and transplant out your tomatoes and peppers after hardening them off. Many gardeners wait until the very end of May or the first days of June for peppers and the most cold-sensitive crops, since cold soil sets them back. There is no prize for planting these early.
June Through August: Plant for Fall
Once everything is in by mid-June, the focus shifts to maintenance and, importantly, planning for fall. The fall garden is one of the most overlooked opportunities in our climate. Keep succession sowing quick crops every couple of weeks so you always have something coming, but watch the cutoffs. Bush beans need warm weather to finish, and MSU Extension puts the last snap bean planting about 12 weeks before the first fall frost, which is about early July in Missoula. Lettuce can keep going through summer if you switch to heat-tolerant varieties, while radishes do best in cool weather, so save them for spring and the fall round below.
For fall harvests, count back from the first fall frost. MSU Extension’s schedule puts fall spinach and kale about six to eight weeks before the first frost, which is early to mid August in Missoula, and lettuce up to about six weeks before, or about mid August. Beets need eight to ten weeks, so sow them in mid to late July, and radishes go in about seven weeks before frost, in early August. Growth slows as the days shorten in September, so fall crops take longer than the packet suggests, and the early end of each window is the safer bet. These crops mature in the cooling weather and often taste better than spring plantings. With a row cover or cold frame, hardy greens like spinach and kale can keep producing past the first fall frost.
September and Beyond
As fall arrives, the season winds down but is not over. Harvest warm-season crops ahead of the first frost, which comes in late September in a typical year but by mid September in about 1 year in 10, and keep picking cold-hardy crops, which often improve after a light frost. Garlic goes in about four to six weeks before the ground freezes, typically mid October according to MSU Extension, to overwinter for next year’s harvest (see when to plant garlic in Missoula). And as beds empty, a layer of compost and mulch sets the soil up for spring.
Kept on a schedule like this, a Missoula garden produces from the first spring greens through the last fall harvest. For more on growing each crop here, see the Missoula Vegetable Growing Guide.
Sources
- Montana State University Extension, Can I Grow That Here? Vegetable Seed and Transplant Schedules
- Montana State University Extension, Successful Home Vegetable Gardening
- Montana State University Extension, Growing Tomatoes in Montana
- Montana State University Extension, Growing Garlic in Montana
- NOAA NCEI, U.S. Climate Normals 1991 to 2020 (Missoula International Airport)