The 4ha Trago Mills garden centre site includes a new glassed garden centre, will create 35 new jobs and hopes to turn over £10m — £5.5m more than the old centre at the retail and leisure destination.
The 3,300sq m covered area will replace an old garden centre that had "run its time", said store manager Peter Davies. He added that the new centre would be "one of the largest in the South West".
A new garden will have a mock beach and wave machine, as well as themed gardens, boardwalks, a ravine, colonnades and up to 15 other water features.
The drive-through area will allow landscapers to buy bulk goods such as compost and paving, which can be loaded straight on to their vehicles by a Bobcat and driven away.
The glassed garden centre will sell thousands of lines including 17,500 species of trees and shrubs.
Owner Bruce Robertson said: "If you can have a drive-through restaurant, why not a drive-through garden centre?"
The project has been in the pipeline for eight years.
Original plans were approved by Teignbridge planners, but it was controversially called in by the Government in 2006 and a public inquiry was held despite the lack of major objectors.
In November 2006 it was given the go-ahead by the then local government minister Ruth Kelly.
TV gardener Diarmuid Gavin cut the ribbon.