The European plum tree (Prunus domestica) has been selected for this project. It is best grown in zones 5 to 9. It can become about 15 feet tall and should start to produce fruit three to five years after it is first planted. European plums are sweet and flavorful. The fruits can be eaten fresh, canned, or dried to produce prunes. Pruning the tree properly is essential for quality fruit production.
Why European Plum Trees Are a Great Choice
There is more than one type of plum tree, and the degree of maintenance involved is one consideration when choosing between the different types. European plum trees require less pruning than the more vigorous Japanese plum trees (P. salicina) and are thus a better choice for those who place a high priority on lower landscape maintenance.
There are two other reasons for Northern gardeners to select a European plum tree (rather than a Japanese plum tree) besides lower maintenance. The European plum tree blooms later, so there is less chance of frost damage, and is more often self-fertile (but always ask at the nursery before buying), eliminating the need to grow another tree as a pollinator.
Even European plum trees need some pruning to achieve the best harvest possible. The good news is that such pruning is fairly easy, takes little time annually, and is quite affordable after the initial outlay involved in buying a few, inexpensive tools.
Why You Should Prune Plum Trees
There are many reasons to prune plum trees, and the relevance of these reasons will depend on factors such as the age of your tree and the time of the year. Pruning in early spring stimulates new growth. Prune in summer to restrict the size of the plant and open up its interior (canopy). Opening up the canopy of the tree (and restricting its size) through pruning, will, in turn, help in a number of ways:
- It promotes good air circulation, which reduces the chances of disease.
- The removal of dead, damaged, or diseased limbs also minimizes disease, as does the removal of crossing limbs that rub against each other (potentially opening up wounds that invite disease).
- The fruit gets more sunlight, helping it grow larger and improving its flavor.
- The increased sunlight also helps the newest branches to prosper.
- The plums will be easier for you to reach at harvest time because you will be working with a tree that is shorter and has fewer cross branches to impede your reach.
Opening up the canopy is hugely important for older trees but obviously is not applicable to young trees (which have no canopy to speak of yet). But, in addition to the stimulation of new growth, young trees derive a critical benefit from pruning: shaping. It is when a plum tree is young that you have to pay the most attention to pruning it in such a way as to create a framework of branches conducive to the tree's long-term health, to the production of well-formed fruit, and to ease of harvesting that fruit.
When to Prune Plum Trees
When you prune a plum tree depends, in part, on the stage of development of the tree. For young trees that you are in the process of shaping, do just one pruning in early spring. For mature trees, to which you have already given the proper shape, prune once in mid-summer (prune lightly, except for those rare occasions on which you need to remove one of the tree's major branches because it has been damaged by an ice storm in winter).
There are specific reasons for the timing of pruning young trees in early spring: It stimulates the formation of new branches at the outset of the growing season, giving them the best chance to grow substantially that year. The wounds made will have less time to heal before the tree starts to grow vigorously in spring, during which period the tree's healing powers are at their highest and small wounds heal relatively quickly.
The earliest pruning done on a plum tree is typically already done at the nursery (to make sure, ask them) before you buy it there in spring; when you get home, all you have to do is plant it. It is a radical pruning in which the trunk (leader) is headed back to about 30 inches tall.
The concern here over healing especially regards to a fungal disease to which plums are susceptible, known as "silver leaf" (Chondrostereum purpureum). Silver leaf exploits pruning wounds to gain entry to a tree's branches. It results in silvering of the infected branch's leaves. It can eventually kill the branch.
Equipment / Tools
- Bypass pruners
- Pruning saw
- Set of work gloves
- Can or bottle of disinfectant
- Paper towels
Create First Scaffold Whorl on the Plum Tree
The next spring, you have three different pruning jobs to perform: Remove all but the best branches, shorten these "best" branches, and head back to the leader again.
Look over the plum tree and determine what its four best branches are at a level of about 18 to 24 inches up from the ground. These are the ones you will keep, pruning off the rest almost all the way back to the trunk, leaving just the branch collar. The "best" branches point upwards from the trunk at roughly a 45-degree angle, are well-formed and disease-free, and spaced at about an equal distance from each other on the horizontal plane (for example, think of a North-facing, an East-facing, a South-facing, and a West-facing limb).
Even on the vertical plane, these branches should not be too close together; ensure 6 to 12 inches of space between them on this plane.
Together, they are said to comprise a "scaffold whorl," because they are primary (scaffold) limbs and form a circular arrangement of like parts.
Reduce the length of each of the four scaffold branches by about half (but make sure each is left with at least a couple of buds). Cut right above the outermost bud that will remain. Reduce the height of the leader by a foot or two, making your cut just above a bud. From this uppermost bud, the new leader will emerge.
Create Second Scaffold Whorl on the Plum Tree
The pruning operation the next spring will be similar. The idea will be to create a second scaffold whorl, located about a foot above the uppermost branch of the first scaffold whorl.
Again, reduce the height of the leader by a foot or two, making your cut just above a bud. Also, repeat the process of selecting the "best" limbs to serve as scaffold branches, using the same criteria as for the first set. The difference this time is that you also have to ensure that this second set is situated such that none of the four branches is growing directly over a scaffold branch in the first set.
Prune back the limbs in the first scaffold whorl by half again, as well as the limbs in the second scaffold whorl. Because the latter are younger, this halving will still leave them shorter than the limbs in the first scaffold whorl. The result is a Christmas tree shape.
Perform Maintenance Pruning on Older Plum Trees
From that point on, pruning is more subjective. Once the plum tree reaches the height you want it to stay at, head the leader back (so that it can't exceed that height) and do not allow a new leader to form.
Prune in summer as needed to keep the canopy from getting overcrowded. Make your cuts back to outward facing leaf buds, because you want new growth to radiate out from the center of the canopy to prevent overcrowding. Leaf buds can be distinguished from flower buds as follows: The latter are the bigger and plumper of the two.
Keep an eye out for spurs. Spurs are groupings of (mainly) flower buds on short, knobby branches sticking out of older limbs. Spurs more than one year old are the source of all your fruit, so make sure you do not mistakenly prune them off.