For most homeowners, the phrase “plant growth regulator” sounds like something out of a chemistry lab rather than a tool for healthy, lower maintenance landscapes. However, more and more plant growth regulators are used, not only to suppress growth to maintain plant size, but to also improve plant health and combat diseases and drought stress.
Plant Growth Regulators (PGRs) are naturally occurring or synthetic compounds that, even in small amounts, dramatically influence plant growth and development. Commercially applied PGRs are a group of chemicals which mimic or block natural hormones within the plant. These hormones are important for the growth of a plant and by regulating them many different benefits can be seen including:
Reduced Maintenance Costs
Plant Growth Regulators, as the name implies, help to regulate the growth of a plant. This is beneficial in reducing new growth on the plant which is helpful when there is a tree with limited space where regular pruning is needed to maintain size. PGRs help to reduce the need for regular pruning thus reducing the annual maintenance costs. These same benefits are applicable to shrubbery, as well.
Enhanced Stress Tolerance
Landscape plants face constant stresses from drought, heat, poor soil conditions, disease and insect pests, and construction damage. Plants treated with PGRs show an increase in ability to combat these stresses. PGRs reduce the size of cells in the leaf and stem but not the number of cells. This creates a more compact leaf with stronger, thicker cell walls better equipped to resist disease. In addition, this more compact leaf is also greener and may produce greater carbohydrates providing greater resources for the plant.
Enhanced Fine Root Growth
PGRs promote fine root growth which increases the ability of the plant to absorb water from the soil. This increases the drought resistance of the plant and improves the health and vigor of the plant.
Enhanced Flowering
Plant growth regulators have shown an ability to enhance flowering in many plants including flowering woody perennials.
Preserved Mature Trees
As trees age, PGRs assist in maintaining health by reducing yearly growth, enhancing stored energy, producing healthier more productive leaves, and reducing age related decline.
How are PGRs applied?
PGRs can be applied either as foliar sprays or soil drenches, each with its own benefits depending on the plant and desired outcome.
Foliar Sprays are applied directly to the leaves and are most effective when done during the plant’s active growth phase. Generally, this is in early spring or just after pruning. This ensures the best results, typically lasting for one season.
Soil Drenches are applied to the soil around the plant’s roots, allowing the PGR to be absorbed and distributed through the plant. This method provides longer-lasting effects, typically 2-3 years, reducing the need for frequent reapplication. Soil drenches can be done year-round, offering flexibility for long-term growth management.
Both methods are effective but choosing the right one depends on the plant size, growth needs, and how long you want the treatment to last.
Plant growth regulators aren’t a one-size-fits-all solution, and they’re not necessary for every plant. However, for high-maintenance trees, drought-prone plants, or when trying to reduce pruning, PGRs can be a cost-effective way to improve the health and appearance of your landscape.