Cleve West and Neil Lucas said they would bring their combined gold medal expertise to private and public garden commissions.
"The new service is launching to coincide with the start of the Chelsea show - the natural habitat for Cleve and Neil over the past few years," said a representative for the venture.
Surrey designer West has won five RHS gold medals for gardens at the Chelsea and Hampton Court shows, and last year won a people's choice award.
Ornamental grass specialist Lucas holds seven consecutive Chelsea gold medals for plants grown at his Dorset nursery Knoll Gardens. "This is the first time they have worked together on a project of this nature. It's an unofficial collaboration and there's no official name for the enterprise," the representative added.
"Cleve's designs are always spectacular," said Lucas. "He has a seemingly innate ability to give people exactly what they want."
West said: "The quality of Neil's plants is first-rate and his knowledge is second-to-none. Working with him will allow me to bring his plantsmanship to any project."
The team will work on any size of project. "It's about learning what each client really wants from their garden and then bringing an edge to the design, while still respecting the integrity of the existing landscape," West added.