Almost 100 nurseries are listed to show at the event, which attracted 141,000 visitors in 2015.
The event will also feature butterflies, Capability-Brown-themed gardens and children's events. The rose marquee will feature a Beatrix Potter garden.
New garden categories will include city gardens and Capability Brown-themed designs. Designers have yet to be announced. Summer and conceptual gardens will also return.
James Wong and Alys Fowler will give talks and demonstrations.
There will be the first children's Saturday, on 9 July, featuring child-friendly events, including the RHS rocket space project.
Show manager Dave Green said: "Every year we try and pack in even more exciting and interactive content to excite and inspire. Visitors will have the chance to experience the amazing gardens by walking through them and getting up close with the incredible designs."