The Benefits of Plant Growth Regulators

Article written by: Alison Herrell, M.S. | Arborologist & PNW Territory Manager with Rainbow Ecoscience

Plantgrowth regulator. That may sound scary or confusing. Why would we want to intentionally stop a tree or shrub from growing? How does that even work? Believe it or not, there are many reasons it may be beneficial to slow the growth of a plant, which include economic, environmental, and plant health factors.

Before we delve into the specifics of plant growth regulators (PGRs), it’s important to know that we already encounter this technology often. PGRs first became popular in floriculture to get uniform plants that would be merchantable in garden centers. Have you ever noticed your house plants start becoming leggy and yellow after they’ve been in the house for a few weeks? That is because the growth regulator applied before you bought them is wearing off.

Early versions of PGRs, Type I growth regulators, were closely related to herbicides and blocked cell division to reduce stem elongation. While Type I growth regulators work well at reducing growth, there can be some unintended consequences of using them including leaf yellowing, distortion, and slight defoliation.

Modern PGRs, Type II growth regulators, work within the plant to regulate the hormone (gibberellin) responsible for cell elongation. This means the plant still produces the same number of cells, leaves, and buds, but those stems are extending 30%-70% less than normal. This reduction in growth can lengthen time between pruning cycles for trees and shrubs growing near infrastructure. For example, the oak tree planted 10-feet from your building or the hedge that gets trimmed multiple times a year.

While PGRs reduce the amount of above ground growth by 30%-70%, they also promote responses that can improve plant health. One positive side effect of growth control is the stimulation of another plant hormone, abscisic acid (ABA). ABA prevents cell dehydration and regulates leaf water loss by allowing stomata in the leaves to respond faster in drought conditions. We also see energy resources being diverted to the promotion of fine root growth when PGRs are applied. This allows a tree to mine more resources from the soil and increases drought tolerance. PGRs also increase the amount of chlorophyll the plants produce, which gives leaves a greener color and allows plant to photosynthesize better. Disease resistance to certain fungal leaf and canker diseases has also been recorded. So, not only can you employ PGRs as a growth management tool, but they can also be employed as a plant health care tool.

The use of plant growth managers can often be overlooked, but when used correctly, can be a substantial tool to help reduce time spent on pruning while also benefiting plant health. Next time you’re walking through your sites think of those hedges, ground covers, trees, and vines that seem to need constant attention. Now imagine, instead of the plants dictating your pruning schedule, you dictate the plants growing schedule.

Less pruning means less wounding for the plant (bonus for the plant), less time your crews need to spend managing your plants (bonus for labor), and less ‘green waste’ to dispose of (bonus for the environment). In 2016, Rainbow Ecoscience performed a series of trials to determine labor savings when incorporating a foliar spray-applied Type II plant growth regulator. The sites selected contained highly manicured shrub hedges from 50-180 feet long and 4-8 feet tall. Over a 12-week period we found pruning time was reduced by an average of 62% when compared to untreated shrub hedges. In another trial, green waste was reduced by 50% over a 12-week period. Managers and crew leaders involved in the trials were unanimous in their positive response to the reduced need to prune. Landscape crews were able to focus on more detail work like weeding and caught up on mowing and edging. They also had less complaints in areas where the PGR was applied.

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Horizon Distributors Acquires

Prowater Irrigation & Landscape Supply

PHOENIX, AZ (March 17, 2023) Horizon Distributors, Inc., a fullservice wholesale distributor of irrigation and landscape maintenance products, announced today that it has acquired the assets of ProWater Irrigation & Landscape Supply, Inc., a Prescott, Arizona-based distributor of irrigation and landscape supply products, effective March 17, 2023. ProWater Irrigation Supply operates two sales and distribution centers serving the Prescott, Arizona and central Arizona market.

“ProWater Irrigation has served the central Arizona market for over twenty years. Adding the ProWater Irrigation team and sales locations to Horizon’s existing Arizona sales center network enhances our presence in the fast-growing Arizona market and provides a strong conduit enhancing Horizon’s service to customers throughout Arizona. Steve and Janice Brooks, ProWater Irrigation owners, will continue working with us to ensure a smooth transition for ProWater’s loyal customers,” said Phil Stephens, Horizon Vice President.

Steve and Janice Brooks added, “Joining the Horizon organization will enhance ProWater Irrigation’s customers’ growth opportunities with expanded product offerings, services and resources. We appreciate the support from the many customers, vendors and dedicated employees that we have had the privilege of working with over the past years. We will work closely with the Horizon team to ensure a strong combined business going forward.”

OnSite OilChange Plus

A big thank you to Rudy Hernandez and OnSite OilChange Plus for sponsoring the February mixer at Lucille’s Smokehouse BBQ.

Onsite OilChange Plus comes on site to your home or business and carefully performs the service there while you work or relax. No mess, no hassle and much less interruption to your day. Cars, Trucks, RVs and Fleets!

In addition to raffling off some great prizes donated by Lucielle’s BBQ and OnSite OilChange Plus, proceeds from the 50/50 raffle in the amount of $250.00 was donated to Operation Freedom Paws.