USDA zone 4 includes much of Wisconsin, Minnesota, the Dakotas, Colorado, Montana and other areas that have long, cold winters and short, cool summers. The climate here is inhospitable to many plants, but gardeners still have plenty of opportunity to grow a garden that produces enough vegetables to eat fresh plus some to preserve. If you familiarize yourself with the limitations and find ways to work around them, you too can grow a robust vegetable garden in zone 4.
Determine the length of your growing season. Although it will vary from region to region, zone 4 generally experiences its last spring frost in mid to late May, and can expect the first frost of fall to come in mid to late September. Your local extension office can give you the specific frost-free dates for your area.
Start warm weather or long season crops indoors early in the spring so that they have time to mature. Plants like tomatoes, eggplant, peppers, squash or melons should also be started indoors four to eight weeks before the last predicted frost. Plant seeds in peat pots or other small containers filled with all-purpose potting mix, place them under a grow lamp or other bright light source and keep the soil evenly moist. Some seeds need warm temperatures to germinate, and you can achieve this with a heated seed-starting mat. The seed envelopes will give you exact instructions for each type of plant. Seed-starting supplies can be found at any garden center.
Plant cool weather crops early in the spring as soon as the ground is warm and workable. Peas, spinach, lettuce, carrots, beets and radishes can all be started outside two to four weeks before the last predicted frost. Some short-lived cool weather crops like lettuce or radishes can be sown again in the early fall for a second harvest.
Harden off the plants you started indoors by placing them outside for an increasing amount of time every day until they are accustomed to life outdoors. You can harden them off and transplant them into the garden after the danger of frost has passed.
Lay down a few inches of mulch, such as dried leaves or shredded straw, around your plants and between the rows of seeds. Mulch helps regulate the soil temperature and can give your plants some protection against cool temperatures in the late spring or early autumn. Mulch also keeps down weeds and adds nutrients to the soil as it decomposes.
Cover your plants with old sheets, tarps or floating row covers at night in the late spring or early fall when a light frost is predicted. The covers will offer your plants some protection and can help prolong the season by a few weeks in the autumn. Remove the cover first thing in the morning so that the plants don't heat up too much and burn when the sun comes out.