I saw a keyhole garden using woven willow to plant turnips, salad, marigolds, peas and beans.
Composting seems to be the key to a keyhole system.
Traditionally used in Africa as a method of planting without having to step on to the bed, it was also a way of conserving moisture and nutrients within the immediate soil located around the heap.
The compost heap is placed in the centre of the key and can also be used as a climbing frame for plants like beans. Any dry green waste and food waste are placed in to the container and as it is broken down, compost is formed and nutrients and moisture seeps in to the surrounding soil.
Very clever… i am going to try!