The proper sealing and insulating of your greenhouse protects the plants inside from a variety of potential hazards. During the winter months, a good seal keeps the cold air from leaking in and causing a possible freeze. Throughout the rest of the year, the seal on your greenhouse can prevent large pests from getting in and prevent the warm air circulating through the greenhouse from escaping.
Check the caulking around the foundation of any type of greenhouse. The gaps where the frame of the greenhouse and the foundation meet should be caulked upon installation. If you have a glass greenhouse, fill in any gaps or holes in the frame with caulking to seal the greenhouse.
Hold the bottom of the plastic down in curtain-style greenhouses with a heavy block of wood or piece of metal on each side. Purchase a piece of metal the same length as the side so that the metal reaches across the entire bottom, or cut a block of wood the same length as the side so that it fits across the bottom. Fold the bottom of the curtain inward so that the bottom lies on the ground, and place the metal or wood across the bottom to seal it against the ground.
Install Velcro strips on the frame of curtain-style plastic greenhouses. Run the Velcro strips down the entire length of each vertical corner post in the greenhouse frame. Leave the two halves of the Velcro strips attached to each other when sticking the strips to the frame.
Peel off the backing on the exposed side of the Velcro strips, one at a time, and press the plastic curtains against the adhesive backing. Put pressure on the plastic until it sticks to the Velcro strip from the top to the bottom. To open the plastic curtains, peel the Velcro apart.