How to Build Your Own Four Season Greenhouse

Extending the growing season is a concern of many backyard gardeners. As anyone who has ever looked to purchase a greenhouse will know, however, they can be prohibitively expensive. Luckily, building your own four-season greenhouse can be a far less costly endeavor, using simple materials and your own labor. Using inexpensive rebar and plastic, you can build your greenhouse in less than a day.

Building Your Greenhouse


Pick your greenhouse site. Situate it close enough to your house that you can run a space heater out to it during the coldest days. Choose a spot with good soil drainage and make sure it will have enough winter sun. Using a chalk bottle and a measuring tape, mark a 6-by-10-foot rectangle on the ground.


Make 6 small chalks dots, every 2 feet, on the outside edge of each 10-foot length of the rectangle. Two of the dots on each side will be at the corners of the rectangle.


Place three 10-foot lengths of half-inch rebar on the ground, one on each side of the rectangle and the third in the middle, all parallel to the 10-foot-long sides of the rectangle.


Drive a 20-foot length of rebar 6 inches into the ground at the edge of the rectangle, one end in each of two parallel chalk dots, hooping the rebar over the 6-foot length of soil in between. Use 16-gauge copper wire to tie each leg of the 20-foot length to the 10-foot lengths on either side of the rectangle.


Repeat with five more lengths of 20-foot rebar, anchoring each to the outside 10-foot lengths for stability as you go along. Lastly, attach the third piece of 10-foot rebar to the top of the row of arches using copper wire.


Drape two pieces of 8-by-4-foot polyethylene over the arch at each end, making sure the inside edges remain vertical and align down the center with a 6-inch overlap, 3 inches past the middle point for each piece. Fold edges over the top of the arch and use small pieces of wire to poke through the plastic at 6-inch intervals, tying it off to secure the plastic to the rebar. Trim the extra plastic on the inside of the greenhouse, but leave the flaps slightly long so you can stake them in rough weather.


Spread a 22-by-10-foot length of polyethylene over the top of the greenhouse, tucking the extra plastic in under the 10-foot lengths of rebar on either side. Inside the greenhouse, pull the plastic through all the way and stake it down using plastic stakes, two between each 20-foot arch. Trim excess plastic on the inside if you wish.

Using Your Greenhouse Year-Round


In very cold weather, ensure that delicate seedlings or fruiting plants, such as late winter squash or chard that are growing after the frosts have begun, get enough heat. Run an extension cord from your house to the greenhouse with a space heater or heating fan attached to it. Place the heater at ground level and ensure an even heat flow by moving it around the greenhouse once or twice a day.


In warmer weather, open the plastic flaps on either side of the greenhouse to allow for airflow. Make sure to open both ends, as opening only one will not allow for a good cross breeze.


In truly hot weather, open up both sides of the greenhouse and run an extension cord with a fan attached out to it to improve airflow, setting the fan just inside one of the doors. If animals eating your plants are not a concern, you may leave the doors open at night to cool the inside of the greenhouse. If you notice sun beginning to scorch your plants, drape shade cloth over them.