Greenhouses help surround plants with heat and retain moisture, creating a humid environment for starting seeds and growing tender plants. Plastic is a good medium for retaining heat and moisture, whether it is plastic wrap or a plastic bottle. Several greenhouse crafts are simple to make by recycling common household materials.
Milk Carton Greenhouse
Build a small greenhouse with a milk carton and a few other household supplies to hold one or two plants. Cut the milk carton in half lengthwise to make the base structure for the greenhouse. Lay the carton on its side with the cut side facing up. Stand and tape drinking straws into the inside of each of the four corners of the milk carton. The straws provide vertical wall support for the greenhouse. Build the top of the frame with more straws placed horizontally. Tape the top frame straws to the vertical straws at the corners. Cover the greenhouse frame with plastic wrap, tape the plastic wrap to the milk carton around three sides; leave the front side open as a flap so you can add and remove the plants.
Soda Bottle Greenhouse
Another way to craft a greenhouse is to slice a three liter plastic soda bottle in half lengthwise. Lay one half of the soda bottle horizontally so that the cut side is facing up. Sand the rough edges of the cut plastic smooth to avoid potential accidents. Fill the cut section of the bottle with potting soil or other planting medium. Plant seeds or seedlings in the planting medium. Rest the other half of the soda bottle on top of the planted section to create the top of the greenhouse. After watering the plants, place the greenhouse in a sunny location. The top of the plastic soda bottle will help hold in the moisture.
Another way to make a greenhouse from a soda bottle is to cut away the bottom 4 inches of a two or three liter plastic bottle. Decorate the bottle with acrylic paints, or leave it as is. Fit the cut opening of the soda bottle over a small plant that is already growing in a pot. The plastic helps retain heat and moisture to help the plant grow.
Connect 1-inch PVC pipes together to craft a greenhouse cover that you can fit over several seed trays or potted plants. Cut four PVC pipes equal to the desired height of the greenhouse. These pipes are the four corners of the greenhouse. Cut four PVC pipes equal to the desired length of the greenhouse, two for the top of the frame and two for the bottom of the frame. Cut four more PVC pipes equal to the desired depth of the greenhouse. Connect the greenhouse frame together by gluing a PVC three-way connector to either end of each of the four corner pipes. Join the four corners together by gluing the pipes cut for width and length into the open slots on the three-way connectors. Cover the frame with plastic wrap to finish the greenhouse.