They are Blackmore & Langdon, Botanic Nursery, Fibrex Nurseries, Hardy's Cottage Garden Plants, Southfield Nurseries, Squire's Garden Centres and Warmenhoven.
Blackmore & Langdon will be displaying delphiniums and begonias. Company director Simon Langdon said: "The RHS Hampton Court Palace Flower Show is a magical experience and the show's success is not just down to the idyllic setting.
"The incredible dedication of all the exhibitors and the trade stands makes the show truly spectacular".
Botanic Nurseries, celebrating its 30th anniversary, will be exhibiting hollyhocks and hydrangeas and hopes to create the largest display of single hollyhocks seen at a flower show.
Fibrex Nurseries is featuring the only display of pelargoniums at this year's show, while Hardy's Cottage Garden Plants will be displaying summer-flowering herbaceous perennials.
Southfield Nurseries will exhibit cacti in flower, while the Squire's show garden is called "Squire's Garden Centre: The Urban Oasis". Sarah and Colin Squires said: "Hampton Court has changed into a complete show with pure horticulture and has opened it up to a wider audience."
Warmenhoven will be exhibiting 20-30 varieties of alliums and amaryllis that have been grown in Holland and transported to Hampton Court Palace. The grower has 13 gold medals from its 25 years of exhibiting.