A greenhouse is a good way to extend your growing season. Northern gardeners can harvest vegetables into the fall, and get started planting seedlings in the spring with a greenhouse, while farmers in the South can try their hand at year-round gardening by planting cool season crops such as celery, lettuce and broccoli in a greenhouse to grow over the winter months.
An inexpensive greenhouse that can be easily put together is a hoop house. A hoop house can be assembled for less than $300 as of 2010, while a similar greenhouse kit may cost as much as $5,000.
Cut one 2-by-4 board into six pieces measuring 4 feet in length.
Attach one of the shorter 4-foot pieces to each end of a 24-foot board with wood screws to make abutting corners. Attach a second 24-foot piece to the other ends of the 4-foot pieces to make a 4-inch-tall raised bed.
Construct a second raised bed by joining two more 4-foot boards to two more 24-foot boards. To do this, abut the corners and screw wood screws through one board and into the other with a drill and Phillips head drill bit.
Place each of the raised beds so that there is a path between them. The outer sides of your raised beds will form the bottom of the greenhouse outer walls. Reinforce the sides of the raised beds by driving rebar 2/3 of the way into the ground. Space the rebar so that there are 6 pieces of rebar on each side of the raised bed. Each rebar piece should line up with the rebar on the other side of the raised bed and with the rebar on the other side of the greenhouse.
Unroll a mat of chicken wire so that it covers the floor of the raised bed. Secure the chicken wire in place by stapling the edges to the inside of the raised bed frame. This will keep wildlife such as gophers or moles from digging into your raised beds to eat your plants. Fill the raised bed with potting soil.
Slide a piece of conduit pipe over a rebar stake on the outside of the raised bed. Flex the pipe into an arch and slip the other end of the pipe over the stake on the other side of the raised bed. Repeat with each of the five remaining conduit pipe pieces.
Wire each of the pipe pieces to its neighbor across the top of the arch to create a ridge for stability. This will keep the greenhouse from collapsing in snow or heavy rain.
Spread out the polyethylene cover and slip it over the top of the greenhouse. Staple the sides to the raised beds at the bottom. Overlap the ends and weigh them down by stapling the remaining 4-by-6 pieces to the ends. Enter the greenhouse by slipping under the ends. On warm days, vent the greenhouse by lifting the ends up to allow air flow through the tunnel.