Cabbage is a cool-season crop that may be grown in summer in the northern United States or in spring and fall in the South. If you have a greenhouse, it is possible to extend your growing season in the North or grow cabbage all season in the South. A greenhouse can help you create an artificially warm environment for raising cabbage. Cabbage performs best if given daytime temperatures between 21.1 and 26.7 degrees Celsius.
Place a thermometer within a greenhouse. Cabbage will survive given minimum temperatures down to -12.2 degrees Celsius, according to Oregon State University. You won't need a heater inside the greenhouse. Monitor the greenhouse temperatures daily. Open the greenhouse doors to lower the internal temperature if it climbs above 26.7 degrees C. Cabbage will bolt (grow a stalk and flowers) if the temperatures become too warm.
Mix a soil composed of one part peat moss, one part compost and one part aggregate such as perlite. Cabbage does best in loamy, well-drained soil.
Drill drainage holes into the base of a 15-gallon storage tub. Cover the drainage holes with a pottery shard. Fill the storage tub with your soil mix.
Create drill holes in the planting tub with a trowel. Space the drill holes twice as far apart as plants placed in garden soil to protect against slugs and rot. The drill holes should be 1/4 inch deep. Place a seed in the drill hole and cover with soil. Water the soil so that it is as damp as a wrung-out sponge.
Group your containers together for improved protection against cold. Cover all of the containers during extreme cold weather with straw to help insulate the cabbage against cold damage.
Harvest cabbage when the heads reach full size but before they can split open.
Check the greenhouse up to four times daily to ensure that the soil is moist and the temperature is correct. Also check daily to ensure that your greenhouse has not been invaded by vermin that will eat your plants. Burrowing animals such as gophers may be attracted to the greenhouse by the warm soil.