With autumn colour all around, David visits the dazzling collection of rare and exotic trees in the arboretum at Castlewellan Forest Park. Head gardener Alwyn Sinnamon picks out some of his highlights, including a slow-growing tree that could become a family heirloom. Nearby, Marc Johansen is considering the future of the tree collection, propagating new plants from seeds and cuttings, while Aidan Murphy is putting autumn prunings to good use by creating a dead hedge. Despite the sunny summer, Mollie Cunningham's pears haven't ripened on the tree, but she knows how to turn them into a tasty treat in just minutes. David visits her at Ballytrim for sweet and savoury ideas to ensure the fruit doesn't go to waste. Also on the programme, Ann FitzSimons joins David in the studio to answer listeners' questions, including one from two Year 7 pupils puzzled by their strangely shaped carrots. Contact the programme on gardenerscorner@bbc.co.uk