Business Smarts: Plant Growth Regulators and Their Potential - The Edge from the National Association of Landscape Professionals

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Business Smarts: Plant Growth Regulators and Their Potential

You can’t slow down time, but you can slow plants with the help of plant growth regulators. These products can be used in various settings and serve as yet another way for landscape professionals to work smarter, not harder.

“PGRs are a powerful yet underutilized tool in the plant health care toolbox,” says Emmett Muennink, an Arborjet South Central technical manager. “There are PGRs for trees, shrubs and turf. The turf industry, especially golf, utilizes PGRs regularly as part of their turf management program. The landscape industry is beginning to see the benefits of PGR use too. There is a growing number of landscape professionals using PGRs, especially on commercial properties.”  

How PGRs Work

PGRs affect plants’ developmental or metabolic processes and regulate growth by altering certain aspects of plant development. A PGR is an organic compound, natural or synthetic, that can change plant growth. A plant growth regulator that inhibits cell division would prevent seedhead or flower formation, while PGRs that reduce cell elongation prevent the vertical growth of a plant.

“Most of the PGRs used in turf inhibit the production of gibberellic acid (GA), which is a major contributor to cell elongation and vertical growth,” says Jamie Heydinger, lawn care segment lead for Nufarm. “In turfgrass, PGRs can reduce vertical growth, which can extend the time between mowing events and the volume of grass clippings when mowing. Further, plants under growth regulation can use carbohydrates that it would have spent on top growth on other plant processes like tillering and rooting, among other things, that can increase the overall health of the turf stand.”

Matt Giese, a technical services manager for Syngenta, says most PGRs take one to two weeks for the effects to be visible and will last for four to eight weeks, depending on the application rate and turfgrass species present.

Heydinger adds that using PGRs is a process, and factors such as rates used, application frequency, turf type and the weather and environment will all impact the chemistry demonstrating a visible impact on the turf.

“However, results like reduced mowing frequency and/or fewer clippings and subsequent cleanup on a lawn or any other turf stand could be noticed within days of an application,” Heydinger says.

When PGRs Should Be Used

Andy Scott, product manager for PBI-Gordon, says whether PGRs are a good fit for your landscape company depends on your objectives. If labor is an issue and you still need to maintain properties, growth regulators can provide the peace of mind that even when you’re not on the job site, the product will regulate the growth of different types of plants.

“What the landscape professional wants is to deliver the best product they can to the customer, keeping the customer happy and reduce their costs,” Scott says. “If they’re not using PGRs to assist with that, I think they should strongly consider looking into implementing PGRs in their program.”

Giese says that PGRs work best on a healthy stand of dense, vigorously growing turf.

Turfgrass stands that are damaged, recovering, thin or stressed are generally not candidates for use,” Giese says. “When turf is growing vigorously, and excessive growth is not desired, plant growth regulators can reduce vertical growth thus reducing the amount of mowing events while under suppression.”

Heydinger says PGRs can be applied throughout the growing season but are the most beneficial during growth flushes, like spring and fall for cool-season grasses and mid-summer for warm-season grasses.  

“Warm-season grasses such as Bermudagrass and St. Augustinegrass respond well to growth regulators due to their rapid growth,” Heydinger says. “Cool-season grasses can also benefit from PGRs with longer regulation and lower use rates. In both warm-season and cool-season turfgrass, using PGRs result in growth reduction, providing the benefit of reduced mowing and clippings, as well as improving the visual quality of the turf.”

While golf course managers have been using PGRs to regulate turfgrass, don’t let this limit your usage of PGRs. Depending on the product type, these can also be used on shrubs, hedges and trees.  

“I tell landscape management companies to think of this as ‘labor in a jug,’” Muennink says. “Inhibiting the growth of shrubs/hedges, tree-form shrubs can greatly reduce man hours and labor costs to maintain those areas. This is especially true for fast-growing shrubs and environments conducive to rapid growth. Professionals should consider utilizing a PGR on any property where shrubs are creating a maintenance or safety challenge or where maintaining a manicured appearance is especially important.”

Muennink adds that they have seen impressive results on hedge rows composed of holly, silverberry, privet, as well as flowering shrubs like roses and azaleas. Trees can also be treated by soil injection or drenching. He says oaks respond really well to PGR treatments.

Application Frequency

Because PGRs promise to cut down on the amount of necessary labor, there is the natural question of how long these products last and how often they need to be applied to maintain control. The answer is it depends on a number of factors, including the product used, the rate it is applied and the type of plant it is used on.

Scott says some PGRs work faster but do not regulate for as long, while other products take longer to slow the growth but regulate for an extended period of time. You should always follow the PGRs application rate as directed on the label for the specific plant type. Higher temperatures will also impact how frequently applications need to be made.

“PGRs last longer in plants in the shoulder seasons like spring and fall because the temperatures tend to be lower,” Heydinger says. “For example, a PGR may provide a level of growth regulation on a cool-season lawn, like Kentucky bluegrass, for six weeks depending on rates in a cool spring, but those same rates applied in the heat of the summer may provide the same level of growth regulation for three weeks.”

Muennink says when it comes to controlling shrub growth, a longer-lasting product could call for two applications a year. He says certain shrubs will break regulation sooner than others depending on the amount of sunlight they get.

“The frequency is up to the landscape management company; what is the tolerance for growth on the shrubs?” Muennink says. “If the property must maintain a perfectly manicured appearance, it will need more intensive management with PGR. If there is more wiggle room for shrub growth, then maybe two applications are all that’s needed.”

In most cases, PGRs are compatible with other products for tank mixes. Obviously, you don’t want to pair the product with anything that promotes shoot growth. Muennink advises not to tank mix PGRS with anything other than surfactant.

“It’s always smart to perform a jar test where you could test that from a compatibility standpoint, and you can test that prior to mixing,” Scott says.   

Jill Odom

Jill Odom is the senior content manager for NALP.