Tomatoes are the crop a lot of Missoula gardeners most want to get right. They want to grow them, they’ve had mixed results, and they want to know why. The honest answer is that growing tomatoes in Missoula is doable, but it requires a different approach than what works in warmer climates. Get the variety right, get the timing right, and most years you’ll have more tomatoes than you know what to do with. Get either one wrong and you’ll be staring at green fruit when the first frost hits in September.
Why Tomatoes Are Challenging in Missoula
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. That gives a typical frost-free season of about 130 days, and less in a cold year or a low, frosty yard. For a full breakdown of frost dates and seed-starting timelines, see the Missoula Frost Dates and Planting Calendar. It sounds like enough, and it is, but tomatoes don’t just need frost-free days. They need warm days and warm nights. Our summers get hot in the afternoons, but Missoula nights cool down fast, and tomatoes need consistent warmth to set fruit and ripen well.
Standard tomato varieties sold at big box stores often need 80 days or more from transplant to produce ripe fruit. Plant one of those in late May and do the math. You’re right at the edge, and any cool stretch in August or a frost that arrives a few days early means you’re harvesting green tomatoes. MSU Extension recommends choosing varieties that ripen in 60 to 70 days for Montana gardens. Tomato days to maturity are counted from transplanting, not seeding, and they vary a little from one seed company to the next, so use them to compare varieties rather than as a calendar.
Choose Varieties That Fit a Short Season
This is where a lot of tomato plans go wrong. It is easy to pick a variety based on what looks good at the nursery or what you grew up eating, rather than what’s suited to a short Montana season. Variety is one of the biggest factors in how tomatoes do in Missoula, along with planting time, warmth, water, and soil.
Stupice is on MSU Extension’s list of recommended tomatoes for Montana. It’s an early, indeterminate heirloom from the former Czechoslovakia, and Territorial Seed lists it at about 60 to 65 days from transplant and describes it as cold tolerant. The fruit is small, about 2 inches across, and flavorful. Glacier is another early choice, a compact determinate plant listed at about 55 days. Early Girl, also on MSU’s list, is widely sold as a start. For cherry tomatoes, MSU’s list includes Juliet and Sungold, an early to mid-season cherry known for its sweet flavor.
F1 hybrids are not automatically the better choice, or automatically earlier. MSU Extension notes that F1 tomatoes are traditionally bred for traits like disease resistance, acidity, sugar content, and earliness, and its recommended list includes hybrids like Early Girl and Juliet alongside heirlooms like Stupice. Look at each variety’s own traits. The key in every case is days to maturity. If the tag says more than 70 days, think carefully before planting it in a Missoula garden.
Starting Seeds and Timing Transplants
Montana’s season is too short to direct-seed tomatoes into the garden. You need transplants, either purchased or started indoors. If you’re starting your own, MSU Extension’s tomato guide says to allow 6 to 8 weeks to grow a good transplant. Count back from the date you plan to set plants out. For a late May planting, that means sowing from about the end of March to mid April. MSU Extension is clear on one point that’s worth repeating: avoid starting too early. A tomato started in early February looks impressive in April, but it’s often root-bound and stressed by the time it can go outside. A healthy six- to eight-week-old transplant usually settles in faster than a stressed twelve-week-old one.
MSU Extension says to set tomatoes out after the danger of frost has passed. In Missoula, unprotected plants usually go in from late May into early June, after a look at the 10-day forecast. Memorial Day weekend is a popular local rule of thumb, not a guarantee. If you want to push the season a little earlier, water walls such as Wall-o-Water can help. They’re plastic tepees filled with water that absorb heat during the day and release it at night. Retailers advertise protection down to about 16 degrees Fahrenheit, but real protection depends on the night and the setup. University of Minnesota Extension says water walls can let you plant about three weeks earlier than normal, though the payoff in yield varies from year to year.
When you transplant, bury the stem deeper than it was in the pot. Tomatoes develop roots along their buried stem, so a deep planting gives the plant a stronger root system. Water well at transplanting and hold off on fertilizer until the plant is established and showing new growth.
Heat, Water, and Keeping Plants on Track
Missoula gets only about 14 inches of precipitation a year (NOAA’s 1991 to 2020 normal for the airport), and summers are usually dry, so tomatoes need regular watering. They’re one of the thirstier crops in the vegetable garden and need consistent moisture to produce well and avoid problems like blossom end rot, which is often triggered by irregular watering rather than a lack of calcium in the soil. Drip irrigation is an efficient setup. It delivers water directly to the root zone, minimizes evaporative loss, and keeps foliage dry, which reduces disease pressure.
MSU Extension’s rule of thumb for vegetables is about 1 to 2 inches of water per week from rain or irrigation, adjusted for soil and weather. In Missoula’s July heat, tomatoes may need the high end of that or more. The goal is consistent soil moisture, not wet soil. Let the top inch or so dry between waterings, then water deeply enough to reach the root zone. Shallow watering encourages shallow roots, which makes plants more vulnerable to heat stress and drought.
Mulching around tomato plants helps a lot in our climate. It keeps soil moisture more consistent, moderates soil temperature, and reduces the splashback that spreads soil-borne diseases onto lower leaves. Straw, wood chips, or even cardboard under a thin layer of compost all work. Organic mulch keeps soil cool, though, so MSU Extension suggests saving it for summer, once the soil has warmed, usually late May to June here.
When Fall Comes Early
Even with good timing and the right varieties, Missoula will occasionally throw a frost at you before you’ve finished harvesting. When a hard frost is in the forecast and you still have tomatoes on the vine, pick anything that has started to show color and bring it inside to ripen. MSU Extension says fruit picked at this stage ripens best at about 65 degrees. Below about 50 degrees, color and flavor do not develop well, so keep ripening fruit out of the refrigerator. Ripe tomatoes keep their flavor best on the counter too, though a few days in the fridge is fine. One study found flavor compounds dropped noticeably after about a week at 41 degrees. Cut tomatoes belong in the fridge.
MSU Extension suggests that once a tomato cluster has set and there’s not enough time remaining before frost to ripen fully, you can cut off additional flowers to direct the plant’s energy toward the fruit already on the vine. It’s a useful trick late in the season when you’re trying to get every last tomato to ripen before the cold arrives.
Row covers over your plants can sometimes buy you an extra week or two in September, which matters when you’re watching tomatoes just starting to turn color as the nights get colder. A lightweight frost cloth over the plants on cold nights can carry them through a light frost, though MSU Extension notes there is no garden protection from a heavy frost below about 27 degrees.
For more short-season choices, see the best tomato varieties for Montana’s short growing season.
Looking to grow more than tomatoes this season? Check out our guides on growing herbs in Missoula and growing peppers in Montana’s short season.
Sources
- Montana State University Extension, Growing Tomatoes in Montana
- Montana State University Extension, Successful Home Vegetable Gardening
- University of Minnesota Extension, Extending the Growing Season
- Zhang et al. (2016), Chilling-induced tomato flavor loss is associated with altered volatile synthesis and transient changes in DNA methylation, PNAS