Sour Cherries (Prunus cerasus) are grown for the tart cherry flavor they impart to pies, jams, and juices. They are more cold hardy than sweet cherries, growing in U.S. Department of Agriculture plant hardiness zones 4 through 9. The trees are generally disease resistant and grow well in the humid conditions of the eastern United States, as well as the major cherry-producing regions of the West. Several techniques can be used to propagate sour cherries.
Sour cherries can easily be grown from seed, though you have no guarantee that the resulting tree will have the same quality fruit as the parent. Seedlings found under mature cherry trees can be transplanted as an easy way to propagate the tree. Otherwise, seeds can be harvested fresh and refrigerated in moist paper towels for several months before planting. This process, called "stratification," mimics the effects of winter temperatures on the seed, unlocking chemical enzymes that prevent germination. Stratified seed sprouts easily in warm weather.
Some growers propagate sour cherries with stem cuttings. They are easy to propagate this way, but the trees may have lower disease resistance and weaker root systems than seedlings or grafted trees. Cuttings can be taken in fall from the top 6 inches of vigorous, healthy branches. Stick the cuttings in a lightweight sterilized potting soil with the growing tips pointing up. Keep moist throughout the winter, and roots and leaves should appear in spring.
When propagating sour cherry trees by grafting, use cuttings from a healthy, productive tree for the top portion of the graft. This is called the "scion" wood and should be collected in late summer. Rooted cuttings or seedlings can be used for the bottom portion, or "rootstock." Several grafting techniques work for sour cherries, but generally the scion and rootstock must be cut so they are the same diameter at the point where they are to be grafted. One common approach is to make a wedge-shaped cut in the top of the rootstock and cut the inverse shape on the bottom of the scion. The two pieces are then securely bound together with grafting tape to ensure good contact and to keep moisture out.
A number of rootstocks have been bred for sour cherries that help the tree adapt to certain growing conditions, increase disease resistance or have a dwarfing affect on the overall size of the mature tree. "Mahaleb" and "Mazzard" are the two most commonly used rootstocks for sour cherry. Of the two, "Mahaleb" is smaller, and more tolerant of cold and drought. "Mazzard" is more tolerant of wet soils and tends to be longer lived. "Gisela" rootstocks are more recently introduced and have a significant dwarfing effect on sour cherries. This rootstock causes early and prolific fruiting.