USDA Hardiness Zone 5 has cold winters with temperatures reaching between -10 to -20 Fahrenheit on a regular basis. The growing season measured from the average date of the last frost in spring to the average date of the first frost in fall is shorter than in zone 6 and higher but longer than in zones 1 through 4. Vegetables grow and, for the most part, have to ripen to maturity within the frost-free time period. Some vegetables such as cabbages, carrots, other root vegetables and Brussels sprouts will tolerate light frosts.
Start Seeds Inside
Begin cool season veggies such as kale, spinach, chard and lettuces inside to get a jump start on spring. The plants will be ready to pop in the garden as soon as the chance of frost is over. Start the cool season vegetables six weeks before the average last date of frost. Harden them off by leaving them outside for increasingly longer periods of time before planting in the ground.
Start warm season vegetables inside as soon as the cold season ones are ready to plant in the garden. Warm season veggies need nights above 60 degrees and days above 70 degrees to do well.
Use fresh potting soil when starting seeds to avoid dampening off, a fungus in the soil that kills seedlings. The seedlings will flop over and die after they're an inch or so high. Don't over-water the seedlings to avoid dampening off.
Cold frames are boxes with sides about 12 to 18 inches high with tops of glass. The glass increases the temperature inside the box much in the same way the windows of a car make the car hotter during summer. Cold frames are used to begin the growing season earlier before the last date of frost in the spring and to extend it beyond the first frost in fall.
Seedlings in pots are placed inside the cold frame. Since the cold frame is warmer than the outside, the seedlings grow faster. When the weather is warm enough, transplant the seedlings to the garden. Keep the glass open for a few days before transplanting to get the seedlings used to the cooler temperatures.
Extend the growing season by planting leafy greens in pots inside the cold frame in late August. They'll have a chance to grow to harvest size before it gets too cold.
Keep the frames warmer by placing gallon jugs of water wrapped in black plastic inside the cold frame. The jugs will absorb heat during the day and release it at night.
Short Maturity Warm Season Vegetables
Zone 5 has a shorter growing season. Choose warm season vegetables that have a shorter time to maturity. If the growing season is only 100 days long, it doesn't make sense to plant a variety of corn that takes 90 days to mature. The corn can't be planted when the ground is cold in early spring. It won't germinate. That means it has to be planted later in the spring, which shaves a few weeks off the season. Other warm season vegetables include tomatoes, eggplant, peppers, beans and squash.
Black or Clear Plastic
Accelerate the germination of vegetables that don't take well to transplanting such as corn, peas and beans by laying clear or black plastic over the row after it has been planted. Even clear plastic will keep the ground warmer, which helps seeds germinate faster.