Tesco has enlisted Fenland Organics of Cambs to offer a 10-item box for £11. Most of the produce comes from four East Anglian growers. It will be launched next month in South London.
Sainsbury's latest attack on this market will offer eight items for under £15 and goes on trial at the end of this month in the East Midlands and East Anglia.
A spokeswoman said: "This is a natural extension of our organic business as well as an entry point for anyone buying but looking for something new." Philip White of box provider Riverford Organics said that shoppers were motivated by concern for the environment and would not go for the retailers' schemes.
He said: "The multiples want a piece of the action, and are not doing this to have a positive impact on pesticides and chemicals sprayed on the landscape."