According both to one of his recent Tweets (picture
here), and the official shortlist here:
The shortlisted plants are:
Anemone 'Wild Swan' - Hardy's Cottage Garden Plants
Begonia Apricot Fragrant Falls - Class Gardens
Brachyscome 'Magenta Delight' - Royal Botanic Gardens Melbourne
Heucherella 'Brass Lantern' - Plantagogo.com
Heucherella 'Solar Power' - Plantagogo.com
Hydrangea macrophylla Avantgarde ('Hedi') - Class Gardens
Lewisia 'Little Mango' - D'Arcy & Everest
Lilium 'Firebolt' - HW Hyde
Lilium 'Julie Fowlis' - HW Hyde
Lilium 'Lankon' - HW Hyde
Lobelia erinus Waterfall Blue Ice (Waterfall Series) - Class Gardens
Nepenthes 'Princess' - Borneo Exotics
Petunia Black Velvet ('Balpevac') - Class Gardens
Rhododendron 'Rabatz' - Millais Nurseries
Sarracenia 'Johnny Marr' - Hampshire Carnivorous Plants
Saxifraga 'Anneka Hope' - Kevock Garden Plants...