Size Matters: Small Is Better !
Trees above demonstrates an overgrown root ball with circling roots, not good!
It is well known among landscape professionals that people want larger plants when they get their landscape done. This is also well known by arborists. The client wants their new tree/plant/landscape to “look great” as soon as it is planted. This is understandable but it is not “best practice”. Let’s consider why, focusing on trees.
First of all, and perhaps most importantly, trees in the West are usually grown and sold in containers. Tree roots do fine in a container for a very brief time, until they reach the sides and/or bottom of whatever container they are in. At that point, when they reach the edges of the container, roots tend to turn. If the root is growing towards the side of the container it will circle around the inside of the pot. If the root is growing down it will turn sideways at the bottom of the container and begin to circle. Roots that have reached the edges of their container are no longer growing in a “natural” manner.
Next, consider the nursery practices where most trees are grown. In general, when a tree reaches a certain size, the nursery will transplant it into the next larger container size, so that they can get a better return on their investment. Usually, the tree is moved to the next container size when it has “outgrown” the smaller container. In these cases, the roots are already beginning to circle inside the container. This condition may be corrected, sort of, by slicing though the circling roots at transplanting, or it may not be corrected at all. If a tree starts out in a 1-gallon container, it will have circling roots 2” from the center of the root ball. When you put this tree in a 5-gallon container and let it grow “to size”, we then have an additional mass of circling roots 4” from the center of the container. Next, let’s assume that the tree is moved up to a 15-gallon container and grown to size for sale (trees are seldom sold in sizes smaller than this). When you buy that tree in the 15-gallon container, it will probably have circling roots visible at the outside of the rootball when you remove the container for planting. You can try to correct this situation and you may be successful with those external roots, but you have not addressed the inner circling roots from the previous smaller containers. This issue continues up into 24” boxes and larger as well.
The third issue is that a tree does much better in the ground than in a typical nursery environment. The longer a tree is in the nursery, the more “nursery practices” are performed on the tree. These practices include seemingly benign things like watering, fertilizing, and pesticide applications. Each of these practices are designed to keep the tree alive and free of pests in the unnatural nursery environment. They are necessary, some might say, to create a sale-able product, but they are not natural. Other practices are much more damaging, including typical nursery pruning (terrible) and nursery staking (also terrible). These last practices are necessary to keep the product within the boundaries of the nursery. Trees need to stand up straight and keep a sale-able (if not beneficial) shape. This is about marketability, not good tree health or structure. In short, the longer a tree spends in the nursery, the more nursery practices it is subjected to, and the more impact on its future growth and viability.
Finally, research has shown that smaller plants quickly catch up with larger plants when planted out. For example, a 15-gallon tree is pretty much identical in size to a 24” boxed tree after one year in the ground, and a 1-gallon catches up to a 5-gallon tree in a year, to a 15-gallon tree in 2 years, etc. Planting smaller trees may not provide the same “instant impact” that a larger tree does, but the smaller one will probably do better in the long run. The smaller tree will have less likelihood of circling roots, and grow more quickly over time. For this reason, we recommend planting smaller trees. As an example, the best way to grow an oak is from an acorn. The next best way is from a small deep-pot (~12” deep and 2” wide). [Note that Ojai Trees buys 15-gallon trees because they are the smallest size readily available in many species].
Jan is a Registered Consulting Arborist and a Board Certified Master Arborist on the Ojai Trees Board of Directors.