Three main types of plum trees (Prunus spp.) are grown in home gardens: the American plum (Prunus americana), European plum (Prunus domestica) and Japanese plum (Prunus salicina), which is the type most commonly grown for its fruits. Most plum trees sold in plant nurseries are hybrid cultivars, the seeds of which do not produce trees identical to the parent trees. Fortunately, plums are among the easiest stone fruit trees to propagate from cuttings, which produce identical copies of the parent trees.
The American plum tree is hardy in U.S. Department of Agriculture plant hardiness zones 3b through 8, and European and Japanese plum trees are hardy in USDA zones 4 through 9. Some of their cultivars, though, are hardy in different USDA zones. For example, the Japanese plum hybrids 'Methley' (Prunus salicina 'Methley') and 'Santa Rosa' (Prunus salicina 'Santa Rosa') are hardy in USDA zones 5 through 9 while the European cultivar 'Empress' (Prunus domestica 'Empress') is hardy in USDA zones 5 through 8.
A plum tree grows best from a hardwood cutting taken in late autumn or winter from 2-year-old growth. A 10- to 12-inch-long cutting works best, and it should have a diameter of 1/4 inch, which is roughly the thickness of a pencil. When choosing a plum branch, or stem, for a cutting, look for:
- Leaf nodes. Choose a cutting with evenly spaced, plump leaf nodes, which are small bumps from which leaves will grow.
- Its position on the tree. Take a cutting from a stem that grows in full sunlight.
Sanitation is a serious concern when growing a plum tree from a cutting. Using dirty tools increases the likelihood of the cutting's failure from bacterial and fungal infections. Before collecting a cutting, soak a knife's non-serrated blade for five minutes in full-strength household disinfectant cleaner or in a solution that is 3 parts water and 1 part bleach. Then rinse the blade with clean water, and dry it well before using it.
Hold the plum tree stem you selected for a cutting, and cut through it at a 45-degree angle directly beneath a leaf node that is 10 to 12 inches from the stem's tip. Use a disinfected knife with a non-serrated blade for that task. Remove the cutting's two sets of leaf nodes nearest the cut or severed end, exposing those leaf nodes with the knife. The exposed nodes will produce roots, which will help the plum cutting survive.
Mix 1 portion of rooting hormone liquid concentrate with 9 parts water in a clean, plastic, 12-ounce soda bottle. The mixture creates a 1,000 parts-per-million rooting-hormone solution.
Dip the severed end of the plum cutting into the rooting hormone solution you made, and hold it there for five seconds before removing it. Plan to pot the cutting immediately, and discard the excess rooting hormone solution you created.
Fill a 1-gallon container, which has multiple drainage holes in its bottom, with a mixture that is one-half coarse sand and one-half moistened milled peat. Stick the leafless part of the cutting into the pot's mixture, and press the mixture snugly against the stem.
Place the container in an outdoor, bright, sunny location with protection from wind. If your climate is cold, then place the pot in a cold frame. If you are in a warm area, set it against a south-facing wall.
Water the cutting's potting mixture if the mixture is almost dry beneath its surface. Add water until it trickles from the container's drainage holes. Don't overwater the mixture.
Check the plum cutting for root growth in four to six weeks. Don't be concerned if it takes two or more months for roots to form. Tug the cutting gently while feeling for its resistance to move, which indicates rooting. If the cutting hasn't rooted after three months, discard it and start with a new cutting.
Aftercare and Transplant
Although plum cuttings root fairly quickly and consistently, they can still fail if transplanted too soon. Let your plum cutting grow in its original container for about 1 month, or until it puts out new growth. Then transplant it to a 1-inch-diameter larger container filled with potting soil, ensuring the new container has drainage holes in its bottom.
Grow the cutting, or sapling, in bright, sheltered conditions and water it on a regular basis until it is well-established. In spring or autumn of its second year, depending on your climate, transplant it into a sunny planting bed with fertile, fast-draining soil. Transplant it in spring if your climate is cool and in autumn if you live in a mild area where frost is rare.
Space standard-size plum trees 20 to 25 feet apart and compact or dwarf varieties 15 to 20 feet apart.