The idea for the greenhouse dates back to Roman times, when cucumbers were grown for the emperor in warm houses made of 'transparent stone,' or mica. The French later tried something similar using glass houses heated with manure. Today, in the extreme northern climates where the growing season is short, and in southern climates where gardeners would like to get a jump on the growing season, a small, portable greenhouse is the answer. A greenhouse uses solar heat and energy to create a warmer climate within the greenhouse than exists outside the greenhouse. This can extend the growing season by sheltering tender plants and seedlings.
Place the perpendicular end of a 4-way joint into each end of one 4-foot PVC section so that the joints are facing the same way. Place an end of each 3-way pipe fitting into each end of the remaining two 4-foot PVC sections. Trace a line around the pipe at the end of the fitting. Remove the fittings, and rough up these ends with sandpaper. Rough up the inside of each fitting with sandpaper as well. Apply glue to the ends of the 4-foot length of PVC and insert them back into the joints. Allow the glue to dry.
Bend each section of 4-foot pipe into a gentle U shape. Insert a section of 2-foot pipe into the pipe fittings to hold the U closed so that it resembles a D shape. Trace the ends of these 2-foot pipes, sand them and glue them as you did in step 1. Wait for the glue to dry before proceeding to the next step.
Join each of the three D shapes together into a long rectangle by inserting the remaining 2-foot pipe shapes into the open ends of the joints. Trace, sand and glue these sections.
Cover the greenhouse frame with clear plastic and snap it onto the PVC pipe using snap clamps. Place a snap clamp at the top of each greenhouse arch, and one on each side. Fold the ends closed using duct tape. You can peel back the duct tape and open the ends if you want to vent your greenhouse.