Keyhole raised beds. This sustainable raised bed technique reduces the need for fertilizers and watering plants because of the central compost structure which leaches its nutrients. Keyhole raised beds or heart-shaped raised beds are a sustainable gardening technique for growing vegetables. The cut-out section in the raised bed is a walkway, enabling you to access the compost heap in the centre of the bed. The compost heap needs to be made of permeable material. I used chicken wire. The compost