Annono cherimola, or cherimoya, is sometimes called custard apple. Native to Ecuador and Peru, this tropical fruit flourishes in mountainous South America with U.S. Department of Agriculture plant hardiness zone 12 climate conditions. Hardy in Puerto Rico and Hawaii, it can be grown from seed. For healthier growth and longer life, saplings are grafted to more mature cherimola rootstock. Horticulturalists use several grafting strategies to increase availability of this uniquely flavored fruit.
Reasons for Grafting
In many countries, cherimoyas are grown from seed. Grafted plants have several advantages over those grown from seed. Grafting either a bud or sapling of a young tree to rootstock of a more mature tree can improve its vitality and hasten its growth to bearing age. In addition, grafting may improve the supply of choice varieties. Robert E. Paull and Odilo Duarte, authors of "Tropical Fruits," rank propagation systems, with seeding producing variable results and cutting-and-rooting a failure; air-layering yields only 5 percent success, and grafting or budding results in 70 percent success. Two grafting methods are widely used.
Budding, or Bud-Grafting
For this method, a bud is removed from a sapling showing signs of vitality: running sap and bud/leaf production. The bud, its adjoining twig and a small piece of wood from the spot at which bud and twig join the trunk, are the only parts of the seedling used for the budding procedure. A T-shaped incision is made in the trunk bark of a tree a year or two older. The bud segment is inserted into the T-shaped flap and bound securely in place. The host tree is tended carefully and the binding kept in place until the bud site shows new leaves, which usually takes several weeks. The host tree is then cut back to a 5 or 6-inch stub, with the grafted bud forming the basis for the new trunk of the tree. This method has been and is still used for the propagation of mangoes and is used commonly with citrus trees.
This method, used routinely with citrus trees, employs the whole trunk of a young sapling along with the roots and partial trunk of an older tree. While bud-grafting is done during the tree's active growth period, usually April through November, cleft-grafting relies on dormancy. Rootstock saplings should be 2 years old, as should grafting candidates. The trunk of a rootstock tree is cut down to a stump of a few inches. A downward cut is made in the middle of the stump; the sapling trunk is inserted into the cleft and bound in place. A successful graft will become obvious when the tree resumes growth.
While grafting can revive an old tree as well as create a new one, cherimoya grafting requires some care in selecting graft partners. While several fruits are closely related in the Annona family, closely enough that some confusion exists about whether a cherimoya is or is not called a custard apple, rooting stock and grafting stock must be identical or very similar, to avoid genetic incompatibilities that spoil the graft. Unlike apple trees, where both crabapple and apple stocks can be grafted easily, Annona members do not work together well. Grafting may make a cherimoya stronger, but it does not shorten the wait until the tree is old enough to bear fruit, at an age of between 3 1/2 and 5 years.
- Stockbyte/Stockbyte/Getty Images