Winter squash is one of the more rewarding crops you can grow in Missoula, but it is also one where our short season fights back. Unlike its summer cousins, winter squash needs a long stretch of warm weather to fully ripen on the vine and develop the hard rind that lets it store for months. The big storage varieties you see in catalogs often need more time than we have, which is why variety choice and a head start matter so much here.
The good news is that plenty of winter squash does finish in our season if you pick the right types and give them a little help getting going. Done well, you end up with squash that keeps in a cool corner of the house well into winter.
Choose Short-Season Varieties
This is a key decision for a winter squash crop in Montana. MSU Extension lists winter squash at about 85 to 100 days from direct seeding, or 60 to 80 days from transplanting, and some of the big storage types in catalogs take longer. Missoula’s median frost-free season is about 130 days (about May 16 to September 26 at the airport, per NOAA’s 1991 to 2020 normals), but those are not all warm growing days. Cool nights in late spring and early fall slow squash down, and in about 1 year in 10 the first fall frost arrives by mid September. Choosing faster-maturing varieties gives you a margin.
Acorn squash is a good short-season choice. It matures relatively quickly, in about 75 to 90 days depending on the variety, and the plants are productive. Delicata is another popular one, a sweet, thin-skinned squash that finishes fairly fast (compact Bush Delicata is listed at about 80 days) but keeps for a shorter time than the hard-rinded types. Buttercup and kabocha types are prized for their rich, dry flesh, and the smaller, earlier selections give you better odds here. For butternut lovers, look for short-season butternuts such as Butterbush, a compact type listed at about 87 days, since standard butternut can be a stretch in a cool year. Spaghetti squash also finishes in a reasonable window and stores well.
Give Them a Head Start
Even with a fast variety, the extra time you can buy at the start of the season helps. Winter squash is a warm-season crop, so wait until the danger of frost has passed and the soil is warm before planting. MSU Extension lists 65 to 85°F as the soil temperature range for squash germination, which matters most if you sow seed directly. That usually means late May or early June here.
To gain a couple of weeks, start seeds indoors about three to four weeks before you plan to set them out (MSU Extension’s range for winter squash), then transplant carefully once the soil is warm. Squash does not love having its roots disturbed, so use larger pots or plantable peat or paper pots and move them gently without breaking up the root ball. That head start can be the difference between a squash that ripens fully and one caught half-finished by the first frost.
Give Them Room, Sun, and Steady Water
Winter squash vines sprawl. A single plant can run ten feet or more, so plan for that or choose bush and compact varieties if space is tight. Give them your sunniest spot, since they need all the heat and light they can get to ripen.
Rich soil with plenty of compost feeds these hungry plants, and steady, deep watering keeps them producing. A layer of straw mulch under the developing fruit keeps it off bare soil, holds moisture, and keeps the squash cleaner. Water at the base rather than over the leaves to reduce the chance of powdery mildew, which can show up late in the season on squash family plants.
Harvesting and Curing
Winter squash is ready when the rind is hard enough that you cannot dent it with a fingernail and the part touching the ground has turned from pale to a deeper color. The stem should be starting to dry and crack. Try to harvest before a hard frost, since frost-damaged squash will not store well. Leave a couple of inches of stem attached, because squash without a stem tends to rot at the top.
Many winter squash types can be cured before storage. Extension guidance is to hold them at about 80 to 85°F for around 10 days to toughen the rind, then move them to a cool, dry place, about 50 to 55°F. Sources differ on how much curing helps, and butternut and Hubbard gain little from it. Do not cure acorn squash at all, since the warm treatment hurts its quality, and plan to eat acorns within a couple of months. Stored well, varieties like buttercup and butternut can keep for months, giving you garden squash long after the season ends.
For more on storage, see Curing and Storing Winter Squash, Potatoes and Onions, and for planting dates across the garden, the Missoula Planting Calendar.
Sources
- Montana State University Extension, Can I Grow That Here? Vegetable Seed and Transplant Schedules
- NOAA NCEI, U.S. Climate Normals 1991 to 2020 (Missoula International Airport)
- Iowa State University Extension, What Is the Proper Way to Harvest and Store Winter Squash?
- Alabama Cooperative Extension System, Harvesting, Curing, and Post Harvest Care of Pumpkins and Winter Squash