Rhubarb is not strictly a vegetable - it’s a hardy perennial that’s ornamental enough to be used in the border, with huge, deep green leaves and pink, red or greenish leaf stalks. It’s the stalks that rhubarb is grown for, much loved in crumbles, with custard or in preserves. However, it’s had a renaissance, with top chefs pairing it with mackerel or roasting it to bring out its sweet and tart flavours