How to Make a Hot Bed for Winter Lettuce

Place a cold frame facing south in a sunny area of your garden. If south is not an option because of shade, then face the frame west. Dig and remove the soil inside the cold frame to 2 feet deep. Smooth the walls and floor of the soil as flat as possible.

Cut four sheets of polystyrene insulation panels to the appropriate size to line all four of the soil walls below the cold frame. Push the panels in place so they are flush against the soil.

Fill the space between the panels with 18 inches of fresh manure. Pack the manure down with the head of your shovel as you add it so there isn’t much room for settling.

Spread sand over the packed manure to 6 inches deep. Position a soil thermometer in the sand about 3 inches deep, making sure it is not inserted into the manure. Close the frame and allow the sand to be heated as the manure begins to decompose.

Check the temperature of the sand every couple of days. The sand should spike around 100 degrees Fahrenheit and eventually drop to below 90 degrees F within one to two weeks.

Place flats of seed trays or pots inside the frame, resting directly on the sand once the sand is holding below 90 degrees. Fill the trays with potting soil and plant your lettuce seeds. Water the soil regularly as the seeds germinate and grow. Harvest the lettuce as needed.