Habitats and habitation. The point is well made that gardens should have an 'untidy' corner for the benefit of wildlife. The massed gardens of town and city offer possibilities for biodiversity greater perhaps than many areas of our farmed countryside. 

 One such corner is shown above in the garden of the house I grew up in. In fact the whole garden is an untidy corner. Every Christmas I have a post-autumn tidy up by which I mean an 'untidying'. I rake leaves into heaps and make piles of cuttings. I do indeed prune and weed but the 'green waste' is not wasted by removing it from the place where it grew.

 There are formal gardens (often very attractive) and gardens that are completely neglected. I suspect that neither is best for biodiversity on a small scale. A combination of tending a garden and neglecting it may well be the most biodiverse if we break that word down into its component concepts: life and variability.

 The idea of 'wild gardening' has become popular although a contradiction in terms. An area that is gardened is not wild but it's possible to let the wild in. And there is what Wendell Berry has called "the teeming wilderness in the topsoil, in which worms, bacteria, and other wild creatures are carrying on the fundamental work of decomposition, hummus making, water storage, and drainage".