A greenhouse is one way in which gardeners nurture and grow tender plants in climates for which they are not suited. Thanks to lightweight plastic and inexpensive construction materials, it is possible for hobby gardeners to build small inexpensive greenhouse so that they can start tender seedlings early or extend their growing season past the first annual frost date in the fall. An inexpensive greenhouse can be assembled or taken down in one day.
Measure the dimensions of your greenhouse and hammer a wooden stake into each corner of the greenhouse with a rubber mallet. Stretch string between each stake and tie it at the ends to mark the boundaries of the building. One good size for a hobby greenhouse is 12 foot wide by 24 foot long.
Hammer seven rebar stakes that are ¾ inch diameter and 3 feet long so that they are halfway into the ground at 4 foot intervals along one wall of the greenhouse. Hammer a second set of stakes into the ground across from the first set and along the other wall of the greenhouse.
Hammer the remaining two sets of stakes into the ground in a line with the first two sets and spaced at 4 foot intervals. This second set of stakes will reinforce the walls of the raised beds.
Place a 2X4 board flush against each row of stakes running the length of the greenhouse.
Cut the remaining 2X4 board in half. Place each end flush with the rebar stakes at either end of the greenhouse structure. The end boards will abut the ends of the lengthwise boards. Hammer the boards together to form two raised beds with a pathway between them.
Slip the end of a ¾ inch, 24 foot long PVC pipe over the top of each piece of rebar running down one side of the greenhouse structure. Flex each pipe downward into a U shape and slip the other end over the rebar against the other wall.
Twist a heavy-gauge piece of wire around the top of a PVC pipe arch on one end at the greenhouse. Unwind the wire down the top length of the greenhouse. Wrap the wire around each arch as you reach it. The wire will provide stability to the greenhouse.
Unroll a piece of polyethylene greenhouse plastic over the top of the greenhouse. Unfold the sides of the plastic and allow them to drape down the sides of the greenhouse. Staple the greenhouse plastic to the wooden base of the greenhouse on both sides. Leave the end of the greenhouse plastic loose to vent the heat from the greenhouse.
Fill each raised bed with a potting soil mix. Never use dirt. Dirt contains microbes that can harm plants in a raised bed environment.