Greenhouses have a number of benefits for garden growers. They allow you to start the season early, provide some protection against freak weather, block out bugs and other pests, and let you grow plants which would otherwise not thrive in your climate. Although a professional greenhouse can be quite expensive, you can build a miniature version out of nothing but a frame, a flat box to hold soil, and some plastic sheeting. Depending on what you happen to have already lying around your house, your greenhouse may cost only a few dollars.
Find or make a base for your mini greenhouse. If you wish to grow your plants directly in the ground with a greenhouse over the top, clear out a rectangular space in your garden. Otherwise, nail 2 by 4s around the top of a pallet to form a container or find an old sandbox or swimming pool to hold dirt.
Measure the dimensions of your mini greenhouse with a tape measure.
Build a frame to sit on top of the greenhouse. If you have boards sitting around, cut them to the appropriate dimensions to make a box to sit on top of the greenhouse. You can also use PVC, metal shelving or other discarded materials.The box should have the same length and width as your greenhouse and be at least 6 inches taller than the maximum height of anything you plan to grow in the greenhouse.
Nail the frame to the greenhouse base. You may wish to reinforce the connection with epoxy or another adhesive to make sure it stays attached firmly.
Attach plastic sheeting to the roof and every side of the greenhouse but one using staples, glue or some other method
Glue another piece of plastic sheeting to the top of the fourth side so that it hangs down like a flap. Tape it closed with a small piece of tape at each hanging corner when you want the greenhouse closed. Remove the tape when you need to access the greenhouse or to ventilate it.