Raised garden beds with lids are called cold frames. They operate on the same principles as solar greenhouses but are much smaller. Most cold frames have hinged lidsnonetheless, it’s possible and helpful to build a removable lid for your backyard bed. A mobile greenhouse top might be removed and stored elsewhere when not being used.
Build the top of this cold frame from doors that are old. Lay the shower door over the raised bed while starting seeds or growing other low crops, like lettuce.
Place dried leaves or other mulch material on top of the shower door near sundown to maintain the heat at immediately, and remove mulch in the morning.
Monitor the temperature in the cold frame with a greenhouse thermometer. Remove shower door during the hottest part of the day, or when the temperature rises too large for your chosen crops. Most garden vegetables germinate at 70 to 75 degrees Fahrenheit. Replace the shower door after in the day.
Pick aged windows with wooden frames for mobile lids that have to be raised over taller crops, like broccoli or flower bushes.
Create an “A framework” with two windows to match over the raised bed. The windows will likely stand on opposite sides of the raised bed, and lean in till they touch each other. This forms a triangle on top of the raised bed.
Assess the distance between both windows about halfway down the flux on one of their sides. Cut a 1-by-4-inch board to 1/4 inch longer than this length. Gently hammer the board into the wooden frames of the windows. Use two nails on each side. Trim the top corners of this 1-by-4-inch board with a small handsaw to make a smooth border, if you prefer. Repeat on another open side of this A-frame structure.
Cover the sides with white plastic sheeting to finish the greenhouse top. Cut the plastic to size and nail or staple to the A-frame. Plastic sheeting is available in garden and home supply centers.