How to Build an Inground Hothouse

Measure the window frame or recycled shower door that will become the hothouse cover. Use tempered glass if possible to prevent injury to yourself, children or pets.

Place your hothouse in an unshaded location, facing south. Dig a 3-foot deep hole as long and wide as the window frame.

Insert a 4-by-4-inch post into each corner. Place the 4-foot posts on the south side and the 6-foot posts on the north side of the hole. Pour 6 inches of pea gravel into the hole. Adjust the posts to vertical, using a spirit level.

Cut six 2-by-6 boards to the width and six 2-by-6 boards to the length of the window frame.

Pre-drill two holes per post, through each 2-by-6 board and into the posts. Screw the boards to the posts with 3-inch deck screws. The side boards should be angled to align with the tops of the posts.

Attach hinges to the window frame. Then, screw the window's hinges to the top of the board on the north side of the hothouse. Add a latch to the window to prevent wind, animals and curious children from opening the hothouse.

Backfill around the exterior of the hothouse with the excavated dirt; this will cut down on drafts as your plants sprout and grow in the hothouse.

Pour 18 inches of fresh manure, such as horse, chicken, rabbit or steer manure, into the hothouse. Add 6 inches of straw and mix well, using a shovel or pitchfork.

Layer 6 inches of shredded newspaper, then 6 inches of potting soil over the fresh manure. Place a thermometer on top of the soil and close the lid.

Monitor the temperature closely. When the temperature peaks, then drops back to 75 degrees Fahrenheit, it is time to plant your seeds. Mist with water daily to keep the soil moist. Open the lid on warm days to avoid burning your plants in the hot sun.