Mike Gilbert of Gilbert Evans, which arranged the deal, said the new building would be a Blue Diamond-standard garden centre.
"Given where it is with its catchment area it should be one of the highest turnover centres per square metre in the country," he said.
"Redfields current turnover is £4m, but the planning consent gained by Malcolm Scott could take this higher when the new centre re-opens fully in two or three years."
Blue Diamond currently has 12 garden centres. Gilbert added: "The leasehold is interesting. Banks are still lending but Blue Diamond taking a lease gives just as good a return as if it had sold the freehold. A lot of people are now looking at the leasehold side."
Blue Diamond's leaseholds include Trentham and Spalding Garden Centres. The Goater family, which owns Redfields, will concentrate on its landscaping business when building is complete.
Gilbert explained: "A lot of owners are looking at retirement in 10-15 years and spending £5m on a new garden centre is a lot of money at that time of your life. A neat way round it is to retain the freehold.
"These days there are not that many straightforward sales. To get the best price you need to look outside the box."