For a garden slap bang in the centre of town, the Phoenix Community Garden is surprisingly tranquil, even on a baking hot day. (We're also told it's the only place in central London you can find frogs, though we didn't see any ribbeters on our visit.) Walk behind the Phoenix Theatre on Charing Cross Road and you'll soon see the railings. Take some time out on a bench, sprawled on the grass or just watching the fish.
The Phoenix Community Garden costs £30k a year to run and gets no funding from the council. You can become a friend of the garden for £12 a year, or one-off donations are always welcomed.
Other little gardens: Elmstead Woods station.