A hotbed is a glass- covered container which is heated by the lower digged in decomposing manure. Here you can sow vegetables already early. Dig a hole 40 to 80 cm deep. If you have a lot of manure, you can make it deeper and therefore hotter. Fill the pit with (horse) manure, covered with 20 to 25 cm of soil. hotbedOrient the tray to the spring sun. If it gets too hot you put the windows (fixed) open. Make sure they cannot be blown away.
With horse manure can be reached after a few weeks a soil temperature to about 30°C (and more), which then slowly decreases over eight weeks to about 20°C. With only straw is the initial temperature 15°C, and then increased to about 18°C. in eight weeks.

Use manure rather not directly in the garden. The roots of plants can burn. And you give microorganisms an opportunity to come back to you in a cycle. Let it digest first.