The fact that I'm writing about something I know (in this case allotments) doesn't make the novel autobiographical. I'm also writing about things I don't know - being a single parent, being an only child, living with someone who struggles to throw things away, and so on.
I'm often asked whether A Song for Issy Bradley is based on my own life. I certainly know a lot about Mormonism, but there are lots of things in the novel that I don't know - I don't know what it's like to be a Mormon convert, or how it feels to be a Mormon Bishop, or what it's like to love Liverpool FC etc.
I don't want to go all Donald Rumsfeld and start talking about known knowns, known unknowns and unknown unknowns, but I like to write about a combination known and unknown (to me) things. Here's some pictures of the known things I'm currently writing about.