Posted: 16/07/2016 at 23:13
Trees that are used for rootstocks are there to restrict the growth of the tree to a size suitable for the garden.Without a variety grafted on top, they will produce an apple, but not likely to be very edible. The top graft is selected for the fruit quality.
Cherries are often grafted on to Colt rootstock, which gives a tree about 10 ft tall. There is a wild cherry growing next door, 15 years old, 40 ft high. The cherries are so high, the wood pigeons and blackbirds have them all.
This might explain it better..