Very few tree fruits have a sweet and sour flavor balance like a tree ripened plum, The smooth skin that surrounds the juicy sweet pulp is crispy and develops a sour taste like a lemon peel when soft and ripe to the touch. Plums when ripened on the tree can develop into color shades of red, purple, blue, yellow and even a ripened plump green, Improved plum tree hybrids are usually grafted onto the rootstock of the wild American plum that dwarfs the tree and gives the tree resistance to nematodes. Call Ty Ty Nursery for pollination information on plum trees.