Let’s be honest, this image of a bonsai tree is misleading. Growth regulators won’t turn your urban forest into a bunch of adorable mini trees and they won’t stop your trees from growing completely. What growth regulators actually do is slow the growth of trees to the point where they need noticeably less trimming while imparting additional benefits that can result in healthier, more attractive trees.
What It Is & How It Works
Growth regulators are EPA-approved chemicals that limit the growth of trees and shrubs. The active ingredient in growth regulators inhibits the hormone that stimulates cell elongation. This means that while the tree continues to produce the same number of leaves, its branches, trunk and roots should grow 40 – 70% less over the following three years. Simultaneously, chlorophyll production is concentrated, root hair density increases and the physical characteristics of the leaves change making the tree greener, and more drought and disease resistant.
Let’s take a closer looks at some of these benefits:
Benefits for the Property
Not everyone understands that trimming actually injures trees. Removing branches creates wounds that can stress trees and allow diseases to enter. Trimming trees less frequently and less aggressively is better for the health of the tree. Obviously, some trimming is necessary in urban environments for clearance, visibility, liability and other reasons. Slower growing trees strike a happy medium between the desire for healthy trees and the needs of an urban environment.
Most trees in urban environments eventually outgrow the space where they were planted. Young trees huddled together attractively or picturesquely lining sidewalks can eventually mature into monsters whose branches hang over roofs dropping leaves and clogging gutters, or whose roots push up concrete and break pipes. Applying a growth regulator reduces these dangers considerably and can extend the service life of trees in planters and parking lots.
During the development of a community or commercial property, young trees are often planted too close to each other to make the property look more established. Additionally, some municipalities have requirements for the number of trees to be planted in new developments. Regardless of the reason, as these trees mature they begin to crowd each other and compete for resources. Eventually, some of them will have to be removed and the stumps ground causing an unwelcome and unbudgeted expense. Slowing the growth of crowded trees extends their usable life and allows the expense of the removals to be spread over a longer time period.
Benefits for the Tree
One side effect of growth regulator is a higher concentration of chlorophyll in the leaves which results in a greener canopy. There are a couple explanations for why this happens but what we know is that because chlorophyll is the molecule trees use to make energy, higher chlorophyll levels mean both healthier and more attractive trees in the landscape.
Another beneficial side effect of growth regulator is that the tree becomes more resistant to fungal and bacterial diseases. The active ingredient in growth regulator affects fungi the same way as a particular class of fungicides which basically means it’s doing double duty. Physiological changes in the surface of the tree’s leaves that make it more difficult for bacteria to penetrate allow an added level of resistance to bacterial diseases.
One side effect we particularly appreciate in the dry climate of Southern California is reduced water stress. The growth regulator causes an increase in the density of fine root hairs which allow the tree to more efficiently take in water and nutrients.
As the growth regulator causes the tree to draw energy away from increasing the size of the canopy, it can focus that energy on creating a strong, stable root system. This is a huge bonus since many of the tree health care issues we treat result from weak or underdeveloped root systems.
The Bottom Line
Growth regulators aren’t right for every tree or every situation but they are excellent as an additional tree care tool in the toolkit of every property manager. Talk to your arborist about how the additional of growth regulators can help you meet your goals for a given property.