The accidental fire at Ruxley Manor was in two two-storey garden centre warehouses.
A 300m cordon was set up because of gas canisters on the site and part of the A20 was closed due to the risk of them exploding.
The crews took four and a half hours to put out the fire at the garden centre, which turned over over £6.9m in the year to December 2007.
A garden centre representative said: "There was a terrific amount of damage. The warehouses and stock and landscaping department have been destroyed. But the whole retail area is open today (Monday) as well as the coffee shop. It's business as usual.