Plastic plant coverings help intensify the sun's rays and heat the air beneath the cover through radiation. This result has been associated with growing plants for so long that it is even known as the greenhouse effect. A hobby greenhouse with a plastic skin is one way in which gardeners with short summers extend their growing season. In the warmer climates of the South, placing vegetables under plastic structures such as a greenhouse is a good way to grow vegetables all winter.
Mix one part peat moss, one part compost, one part sand and ½ part composted manure into a soil-free growing medium. Sterilize the soil-free mixture by placing it into a baking bag and a roasting pan. Place it in an oven set to 250 degrees Fahrenheit. Use a meat thermometer to gauge the internal temperature. Bake until the mixture’s internal temperature reaches 180 and all disease microbes have been killed. Take the bag outdoors to open it. Baked potting mix is smelly. Allow the soil to cool and fill your raised beds or containers with it.
Plant seeds for winter gardens in late summer or early fall. Most seeds packets have the days until a plant reaches maturity printed on the back of the packaging. Count backward from the day you would like to harvest to determine the best day for planting seed. Plant seeds in furrows or drill holes to the depth recommended on the back of the seed packages. If this information is not listed on the packaging, plant each seed twice as deep as the seed’s width at its widest point.
Space plants farther apart in winter than you would in summer. Plants are more susceptible to damage from rot or slugs in winter.
Place a thermometer in the greenhouse. Check the greenhouse temperature up to four times daily. Open a door to vent the greenhouse any time the temperature becomes too hot for plants. Plants such as lettuce will go to seed if the temperatures become too warm. Mulch around your plants at night with straw or cover them with garden cloches, which are plastic, bell-shaped containers. This will protect them from cooler weather. Move a space heater into your greenhouse at night and use it to raise the ambient temperature in the greenhouse.
Harvest crops when they become ripe.