Gardening can be viewed as a largely pointless hobby, but the evangelical zeal and camaraderie it generates is unique. Charlotte Mendelson is perhaps unusually passionate about it. For despite her superficially normal existence, despite the fact that she has only six square metres of grotty urban soil and a few pots, she has a secret life. She is an extreme gardener, an obsessive, an addict. And like all addicts, she wants to spread the joy.