Why there’s more to PGRs than meets the eye

Lawn growth regulators reduce the frequency of mowing and create a healthier plant. (Photo: Henfaes/iStock / Getty Images Plus/Getty Images)

As the name implies, plant growth regulators (PGRs) regulate the growth of a plant, allowing landscape professionals to spend less time mowing and trimming.

Mark Lucas, director of landscape solutions at Rainbow Ecoscience, and Lisa Beirn, Ph.D., technical services director from Syngenta, share what you need to know about PGRs.

Application timing

Lisa Beirn

As with most turf and ornamental applications, timing is crucial, Beirn says.

“In general, most PGR applications can begin in the spring to healthy, actively growing turf before the onset of stress,” she says. “Always consult the label to ensure the product is labeled for use on the desired species and that no other restrictions exist.”

Other restrictions could include applications in the summer, Beirn adds. In that case, as turf enters dormancy or experiences heat or drought stress, lower rates or withheld applications are the way to go until growth resumes.

Fall is another potential application time for lawn care operators (LCOs), according to Lucas. A fall application will help limit the growth of turf for LCOs who may manage warm-season lawns overseeded with cool-season turf.

Mark Lucas

“September through November would also be a good time,” he says. “We really advocate for those two application windows. Fall and spring are two great times that should provide three or more months of control.”

Application timing may vary based on your location as well. LCOs in warmer climates, where turf and ornamentals have longer growing periods, may want to consider additional applications to ensure full coverage while turf grows.

“Geography can influence when turf breaks dormancy in the spring,” Beirn says, “so the timing of initial PGR applications may vary across regions. In addition, locations with a prolonged growing season may benefit from additional applications.”

Methods of application

Application timing is important, but so is the mode by which an LCO applies a PGR. Lucas says uniform coverage is a must, which starts with the equipment you use.

“We prefer a motorized unit for application versus a hand-pumped sprayer,” Lucas says. “Whether it be a 50-gallon sprayer or, in some cases, we’re seeing battery-operated backpacks, because these products require proper coverage to get the full effect.”

How it works

PGRs aren’t new; LCOs have used them in turf since the 1950s, Beirn says. Recently developed PGRs are a bit more subtle than their predecessors, however.

“PGRs developed before the 1980s slowed the growth of the turf by inhibiting cell division,” she says. “Today, however, most growth regulators inhibit the plant hormone gibberellin.”

Newer formulated PGRs — also known as type two regulators — while suppressing the gibberellin hormone, trigger other hormones within the plant, including those in the roots. This process can lead to enhanced drought tolerance for turf and shrubs treated with type two PGRs.

“We have some studies showing that plants treated with a PGR and other type two regulators have become more drought tolerant,” Lucas says. “That’s because the PGR is limiting that vegetative growth and making the plant utilize it elsewhere. It’s taking that energy into root production.

More benefits

Beirn says additional benefits can include seedhead reduction and enhanced establishment. Similarly, industry research has also shown that PGRs can aid in drought tolerance for turfgrass and shrubs, Lucas adds.

In addition to practical benefits like limiting growth and better root structure, Lucas says PGRs can provide an aesthetic benefit.

“We’ve seen over time that PGRs are helping with flower performance,” he says. “The plants will actually become greener because of the chlorophyll that’s being produced in the plant because you aren’t pruning off flowers and there are more appearing on the plants.”