I always do my thinking when I am driving. I have been thinking about the key hole garden a lot and it seems to me that it can be more than just a garden in the summer but a compost a cold frame and a raised bed which it is! the screen compost is the start or some form of a compost holder. Lets say a 2 foot round screen sticking up about 3 feet high! Now you build your keyhole garden around it to about 18 inches to 2 feet. The screened compost holder will be about a foot above the raised bed. I would make the raised bed about 5 foot in a circle with a pie slice out of it to allow to enter to put in the compost!
The soil fill for the bed would be about 6 inches below the top of the round enclosure ! Early in the spring a plastic cover would be put over the whole bed including the compost making it look like funnel turned upside down with the compost screen also covered. This would be your cold frame that would get a little heat from the compost also! Bricks would hold the plastic over the key hole cold frame.
The cover could be opened in seconds to add to the compost! I am going to make one in about 2 weeks and may use land scape timbers or brick Think about it it would solve 4 different ways to garden in one and also look great! In may or june use it for a raised bed with the compost feeding the raised bed and also adding water to the screen that feeds the bed from the bottom and sides! Comments & Suggestions?? I have about 6 cold frames and will convert two of them. Great exciting project!