A reader recently asked about suckers that seem prolific on their Spring Snow crabapple. Ornamental fruit trees are prevalent in the Treasure Valley and many people deal with the frustration of continual clipping of the growth that comes out of the base of their trees. This article will explore what that growth is, what causes it, and what you can do about it. As you come to understand what the tree is trying to do, perhaps you will find renewed appreciation for the wonderful diversity of the plant kingdom.
What is a "sucker"?
A "sucker" is a term used to describe growth that forms out of the trunk, limbs, or roots of plants. In this discussion we will focus specifically on the growth that forms at the base of the trunk in the zone of transition from the trunk to the roots. This growth is formally called an "epicormic sprout".
Why do trees grow suckers?
Epicormic sprouts (suckers) are sprouts that occur from either wounds that trigger specialized tissue near the wound to produce a shoot or from specialized tissues that trigger in response to stress or possibly growth-regulating substances. It is not fully understand what triggers sprout growth, but it is likely there are a combination of factors that may trigger different kinds of growth responses. Suckers also are vegetative growth that helps the tree produce more photosynthates (plant "food"). Some species, like aspen, use suckering as a propagation strategy. Each sucker is genetically identical to the parent. This is a form of asexual reproduction and is beneficial for a species that is perfectly adapted to the environment it is in. Fruit trees and many berries and brambles use this same strategy to create new plants. Obviously, if the environment were to change just enough, this strategy would not prove to be the best means for propagation. Fortunately, plants also reproduce sexually, insuring their survival potential.
Do all trees produce suckers?
Every species of tree produces its own rate of response to outside factors that affect it. Some species respond little and others a lot. Fruit trees are notorious sucker producers. That applies to ornamental fruit trees as well as fruit bearing trees. Trees that are fast growing and short lived also tend to use suckering as a reproductive strategy (usually in conjunction with sexual propagation which is by seed production). Locally, our native black cottonwoods use both strategies to persist along the Boise River.
What you can do about suckers?
There are different strategies used to slow down the rate of suckering. Most people just cut them off as they grow, and that is really all you can do. You may also apply a growth regulating hormone to the site of the freshly cut sprouts and that will significantly slow down formation of new sprouts at the cut site. Heavy to moderate pruning will significantly stimulate new vegetative growth. When you prune, you are doing two things: wounding and stressing the tree and also removing photosynthesizing components. The tree responds two-fold as it attempts to replace the lost leaf surface that is responsible for generating sustenance for the tree. Wounding stimulates the tree to push new epicormic shoots. The very act of a mechanical wound triggers specialized tissues to react by pushing out a new shoot. Understanding this function and tree response can help you to carefully manage pruning on species that are more prone to producing an abundance of suckers. Likewise, a proficient knowledge of proper pruning can help you make the most of the work that you do. Pruning is one of the more important acts performed on a tree. It will be discussed more in depth in a future article. Suffice it to say, improper pruning can damage your trees, which is not something you want to do to your property value enhancements!
What happens if suckers are not removed?
Most trees purchased from nurseries are actually made up of two parts. The top portion of the tree, the part you bought because you like the looks of it, is one particular variety of a species. That top portion has been grafted onto a root stock. Many fruit trees are prone to certain kinds of insect pests and diseases. There are a large variety of rootstocks that are resistant to the many problems that plague fruit trees. Some rootstocks serve to reduce the potential size of a tree, which is where we get dwarf and semi-dwarf trees. When you see suckers at the base of your tree, you see growth coming out of the root stock, not the top of the tree. If you were to let the suckers grow unchecked, you would have a very odd looking combination tree. The top portion would not look like the growth from the base. It is best to remove the suckers as they are just forming, and by simply pulling them off while they are still small, you can slow down the newer growth. They rub off easily when they are just forming.