Three is the magic number for compost bins. This facilitates a three year rotation. One filling up with new cuttings, clippings etc. One full and in the process of composting. One well rotted with lovely loamy compost.

 As it happens the music school has two, both enormous. One is almost full of composting matter and the other almost empty of actual compost. Never mind, two is better than one or none. And the fungi, bacteria and invertebrates are hard at work...