Owner Chris Smith said Pennard Plants will build an allotment garden at the RHS show. Pennard will host an allotment shop as well as building the main show feature and organising demonstrations of apple varieties, juicing and tastings.
Raymond Evison Clematis will also be exhibiting. The RHS is delaying the announcement of the other nursery exhibitors until later this week.
Seasonal competitions will be returning to the Autumn Harvest Show including the botanical photography competition, which will feature a variety of subject matters from botanical graffiti to tree peonies of China and Japan. The show will also host several other competitions including the ornamental plant, fruit and vegetable, bonsai kai and British National Carnation Society.
In addition, the RHS is holding several Taste of Autumn events at Harlow Carr, Hyde Hall, Rosemoor and Harlow Carr.
Meanwhile, Pennard says Agapanthus is the hot flower of the moment and the firm is now growing it as a main crop in the summer.
Smith said: "People are finding that they can grow them fairly easily. A lot were lost last winter because they had no protection in gardens. But we have some good new varieties. People want them in their gardens so they can get away from only seeing them on holiday in Madeira. It's a holiday thing. People bring them back and then they want all the different varieties. It has been a good summer for us with Agapanthus. Last year everyone wanted white. Everyone wants dark blue ones this year."
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