There’s a right window for buying vegetable starts in Missoula, and it’s narrower than most people expect. Buy too early and you end up with rootbound plants sitting under grow lights for weeks while you wait for the weather to cooperate. Buy too late and you’re picking through what’s left, planting into a season that’s already getting short.
Missoula’s Growing Window Is Real
Missoula sits at about 3,200 feet, and NOAA’s 1991 to 2020 normals for the airport put the median frost-free season at about 130 days. The median last spring frost is mid May (about May 16), 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. Your own yard can run earlier or later depending on how much cold air pools in your area.
That window of roughly mid-May to late September is what you’re working with for warm-season crops. For tomatoes, peppers, cucumbers, and anything else that needs real heat to produce, getting your timing right on both ends matters more here than it would in a longer-season climate.
The Problem With Buying Too Early
It’s tempting to pick up tomato starts the first warm weekend in April, especially when nurseries stock them early. But buying starts weeks before you can plant them creates its own problems. Plants sitting in small cells will eventually become rootbound. They go through cycles of drying out and being watered. They lose the compact, healthy growth habit that makes a start worth buying in the first place.
By the time they go in the ground, they can be a different plant than what you bought. A start bought closer to planting time, hardened off, and planted on schedule usually settles in faster than one that spent three weeks waiting in a small pot.
If you do buy early because you find something you really want, keep the plants somewhere bright, water carefully, and be ready to pot them up into a larger container if they start to get rootbound before the weather cooperates.
Cool-Season Crops Can Go Out Much Earlier
Not everything needs to wait until late May. If you’re growing lettuce, kale, chard, spinach, broccoli, cauliflower, or peas, you can start a lot earlier than most people do in Missoula. These crops tolerate light frost, and many of them prefer cooler temperatures anyway.
MSU Extension’s planting schedule lets hardened broccoli transplants go out as early as about six weeks before the last frost, and cauliflower about three weeks before. In Missoula, mid April to early May is a comfortable window for most yards. Lettuce and spinach can go out even earlier with a little row cover protection on the coldest nights.
For cool-season vegetables, mid to late April is a reasonable window to start buying and planting. The Missoula Farmers Market usually carries some cool-season starts by early May, though vendors and dates change from year to year, so check before you go. If you want to start earlier, these are the crops worth planting first.
Warm-Season Crops: Late May Is the Right Target
Tomatoes, peppers, cucumbers, squash, melons, and basil cannot take frost and grow slowly in cold soil, so they need warmth in the soil, not just the air. MSU Extension advises setting tomatoes out after the danger of frost has passed, and the same goes for the rest of this list. University of Minnesota Extension suggests waiting until night lows stay above about 50°F for peppers. In Missoula these crops usually go in from late May into early June, after a look at the 10-day forecast. Memorial Day is a popular local rule of thumb, not a guarantee.
The air can feel plenty warm in early May while the ground is still too cold. This is especially true in shaded yards or in areas with heavy clay soil, which holds cold longer than sandy or amended beds. A basic soil thermometer costs a few dollars and shows you how quickly your beds are warming.
A good approach for warm-season starts is to buy them in mid to late May, ask whether they have been hardened off, finish hardening them at home if you are not sure, and plant once the forecast looks settled. You are not losing time by waiting for warm weather. You lose time when you plant into cold soil and the starts just sit there doing nothing for two or three weeks.
When It’s Actually Too Late
There is a point where planting warm-season crops stops making sense, and in Missoula that point comes earlier than people expect. The way to figure it out is to do the math. Take the days-to-maturity number from the plant tag, which for transplants usually counts from planting day, and count forward from your planting date. If you plan around the median first fall frost of about September 26 and your tomato needs 70 days, you need to be in the ground by mid-July at the absolute latest. Realistically, late June is a better cutoff, since days-to-maturity numbers assume ideal conditions, not Montana shoulder-season temperatures, and in about 1 year in 10 frost arrives by mid September.
If you’re standing in front of a nursery display in mid-July thinking about tomatoes, the honest answer is that it’s too late for a reliable harvest. You might get something in a warm year, but you’re gambling on a long fall.
Cool-season crops are a different story. You can plant kale, chard, and lettuce through July and into early August for a fall harvest. Broccoli needs more lead time, and MSU Extension’s schedule ends its plantings about 14 weeks before first frost, which is around the third week of June here. Our Missoula planting calendar has fall windows for these crops, and they are worth using.
For what to check once you are at the nursery, see what to look for when buying vegetable starts.
Sources
- NOAA NCEI, U.S. Climate Normals 1991 to 2020 (Missoula International Airport)
- Montana State University Extension, Can I Grow That Here? Vegetable Seed and Transplant Schedules
- Montana State University Extension, Growing Tomatoes in Montana
- University of Minnesota Extension, Growing Peppers