Until 10 July, the Devon garden will show off scented blooms, floral workshops and unusual cultivars for sale.
RHS Garden Rosemoor has one of the UK's largest collections of roses, with two dedicated rose gardens bringing together 200 different varieties, from climbers to container varieties.
Highlights from the festival include a botanical art exhibition, guided tours, expert advice from RHS horticulturists and David Austin Roses, a floral market, children's activities and a rose trail.
Events include a Rose Weekend on 18 and 19 June featuring a floral-themed craft and food market with over 40 stalls in the Terrace Marquee.
The Rosemoor Garden Kitchen will be offering a series of rose-inspired and rose-infused foods, from meringues and rhubarb cakes through to Turkish delight coffee.
A late opening on 7 July will allow visitors to enjoy the gardens at dusk as the roses release their evening scent. Visitors can vote for their favourite scented rose at daily smell-athon sessions, with the winner announced at the end of the festival.
The RHS is also publishing The Rose: The history of the world's favourite flower in 40 roses (Carlton Books, £35) along with an exhibition of original 18th- to 20th-century watercolours of roses from the RHS archives in the Lecture Hall.