Growing Season and Frost Dates
The growing season is the amount of time between frosts in a given area. The growing season in Wyoming changes greatly depending on which area you live in. In the Upper Green River Valley, Star Valley and Jackson Hole, for example, there is "practically no growing season" for tender crops that become damaged by light frost, says the Western Regional Climate Center. The main agricultural areas across the state have a growing season of approximately 125 days. The last frost is May through late July across the state; first frost dates average August through early October.
Choosing the correct vegetables is as important as timing. Many warm-season vegetables that require long growing seasons aren't appropriate for Wyoming. These include tomatoes (Solanum lycopersicum), peppers (Capsicum spp.), pumpkins (Cucurbita maxima), sweet corn (Zea mays var. saccharata) and melons (Cucumis melo). However, many of these species have cultivars which mature much faster, notes the University of Wyoming Cooperative Extension; look for varieties which can grow and mature during your region's growing season.
Starting your seeds indoors is an ideal way to get a head start, extending your growing season by weeks in some cases. If you want to plant warm-season vegetables that take more time to mature than your growing season allows, indoor starting can yield transplant-sized plants that are already growing by the time most of the country is ready to plant seed. In general, start your seeds indoors four to six weeks prior to the last frost date. Place the seed tray in a warm, sunny window or other location and water regularly. Be careful during transplanting; breaking or damaging the roots can kill many tender vegetables. Some warm-season crops have shorter growing periods and can handle the short seasons throughout much of the state. Many herbs grow quickly, as does summer squash (Cucurbita pepo).
Cool-season crops are hardy against frost and, in some cases, snow cover. These crops are ideal for Wyoming's short growing seasons. Examples of cool-season vegetables include the Brassicas: broccoli, cauliflower, kale, cabbage, and many greens are all varieties of the species Brassica oleracea. Onions (Allium cepa), garlic (Allium sativum), carrots (Daucus carota) and radishes (Raphanus sativus) are also cool-season crops. Plant these selections two to eight weeks prior to the first frost date for your region, depending on the length of time they take to mature.