Dual Plum - Fruit Prunus domestica 'Bleue de Belgique' + 'Reine Claude d'Oullins' Dual plum (Prunus domestica) has two succulent varieties on one tree. The juicy Bleue de Belgique with purple skin and tender, yellow flesh and the Reine Claude d'Oullins, whose yellow flesh has a sweet, pronounced aroma. They have been grafted onto one rootstock and pollinate each other. These plums are ripe in the months of July until August. Height supplied 80-100 cm.