The recent hot spell has meant farmers are now having to mature pumpkins in special storehouses, rather than leaving them in the fields.
Derek Benjamin, pumpkin buyer, said farmers had to change methods in order to supply pumpkins for Hallowe’en.
Sainsbury is also introducing mini pumpkins called ‘munchkins’ designed for roasting or for children to sculpt.
Meanwhile, the retailer’s main pumpkin supplier, Barfoot’s of Botley, has taken on a flock of trained geese to combat pumpkin thieves. Jon Barfoot said: “The geese make more noise than dogs.”