Georgia has a temperate, coastal climate. Most of the state falls between USDA hardiness zones 7 and 8, with a small portion of the northern part of the state within zone 6. Because of this, the state has a mild, temperate climate. Gardeners who want to extend their growing season year-round can grow cold-hardy vegetables, such as lettuce and celery, in greenhouses, cold frames or polytunnels.
Select a site for your greenhouse that is in full sun. The greenhouse will heat up by day, and at night it will hold in heat and keep freezing temperatures away from your plants.
Lay out the footprint of your polytunnel greenhouse by hammering stakes into the ground at the corners of the greenhouse. Stretch string between them to act as a guide.
Drive six pieces of 24-inch rebar two-thirds of the way into the ground using a mallet all along one side of your greenhouse. Space the rebar pieces evenly along the wall. The rebar will anchor the frame of your greenhouse in place. Drive the other six pieces of rebar into the ground along the other side of the greenhouse, being careful to place them in alignment with the first six pieces.
Place PVC pipe over the rebar on one side. Gently flex the pipe into an arch and cover the rebar on the other side of the greenhouse with the pipe. Stretch a piece of wire across the top of the pipe at the top of the arch and again on each side. This will improve the stability of the greenhouse.
Construct a raised bed on either side of your greenhouse to grow your vegetables in by joining the 24-foot 2-by-4s to the 4-foot 2-by-4s at the corners with wood screws, to form two large rectangular boxes. Place each raised bed flush with the rebar on one side of the greenhouse.
Fill each raised bed with potting soil. The majority of Georgia soil is a red clay that is the result of Georgia's humid climate and the weathering effects on rocks. Plants typically grow poorly in heavy clay soil. In addition, the soil in raised beds will heat in a greenhouse more quickly.
Cover the frame of the greenhouse with polyethylene plastic. Pull the plastic taut over the greenhouse. Roll the bottom edge and staple it to the outside of the raised beds. Leave the ends loose and weigh them down with rocks. On warm days, pull the plastic on the ends up to vent the greenhouse. Pull the ends back at night to keep the greenhouse warm. Place a thermometer in the greenhouse
Select cold-hardy vegetables to grow in your greenhouse in winter. Good examples of cold-hardy vegetables that thrive in a greenhouse in Georgia winters include broccoli, cabbage, kale, lettuce and celery.
Check the greenhouse twice daily. Vent the greenhouse anytime temperatures raise higher than your winter vegetables can stand. Test the soil by inserting your finger up to the second joint. Water when the soil becomes dry. Soil should remain as damp as a wrung-out sponge.