Growers Developing Strategies for Better Plant Growth Regulator Use in Greenhouses

SunPatiens SuperNova 50 Liner Four Star Greenhouses
This is a comparison of SunPatiens Compact Blush Pink at Four Star Greenhouse at six weeks. The plant on the left was grown from a Standard 84 liner, while the plant on the right was grown from a Supernova 50 liner.

Proper management of plant growth, whether through chemical, mechanical, or cultural methods, is critical to producing a quality crop. Greenhouse Grower recently asked a couple of leading growers about the strategies they are using to reduce their reliance on plant growth regulators (PGRs), while increasing consistency in production. Here’s what they had to say.

Four Star Develops SuperNova Liner

Dennis Crum, Director of Growing at Four Star Greenhouse in Carleton, MI, says one of the ways the company has adapted its production practices to cut back on the use of plant growth regulators is by adjusting crop times as efficiently as possible to allow for either fewer applications or lower rates.

“We try to match the crop to the proper environment,” Crum says. “We have also increased use of DIF, a technique involving temperature control for the purpose of controlling plant internode length and thus elongation rates in crop production.”

Other steps Crum says his growing team at Four Star has taken include the elimination of some high-maintenance crops, finishing crops in outdoor and open-roof environments, and using more PGR drenches and less sprays.

“We have also begun to do more liner drenches before planting to reduce the need of PGR applications later.”

Perhaps the most effective strategy Four Star has taken to reduce its reliance on PGRs is the development of the SuperNova liner plant for growers to use in 4- to 6-inch pots.

“These plants are aged, bulked, and initiated for faster crop timing and turns,” Crum says. “We also treat them here with PGRs as needed, and this greatly reduces or eliminates the needs of the final grower to treat later with PGRs.”

Growing SuperNova liners for small container production can help growers net faster turns and more consistent flowering, Crum says. SuperNova crops grown at an average daily temperature of 65°F can be ready and in bloom in as early as four to five weeks, compared to a typical eight to 10-week growing cycle from Standard 84 liners.

The bud-initiated liners are treated to flower faster, develop better branching, and flower consistently — with fewer inputs. No pinching is needed and they require less growth regulating than Standard 84 liners.

Superbells Tropical Sunrise (Proven Winners, Pleasant View)
Superbells Tropical Sunrise from Proven Winners in a 72 Enhanced liner at Pleasant View Gardens after a pinch and applications of ethephon (Florel) and daminozide (B Nine) to develop branching and uniformity, and paclobutrazol (Bonzi) to stack the shoots and rightsize the canopy to the finished pot.

Pleasant View Groups Plants Based on PGR Response

“Overall, our PGR use has increased in efficiency over the years as we’ve developed more targeted products, enhanced liners for example, to help our customers turn their space faster, and with less labor,” says Mike Goyette, Operations Manager at Pleasant View Gardens in Loudon, NH. “Our processes have improved by focusing in at the variety level and grouping plants based on their response to certain PGRs. This allows us to be more consistent in developing branches, reducing elongation, and right-sizing plant canopy to pot size while reducing over application instances.”

It’s not just plant growth regulators, Goyette emphasizes. Lighting, temperature, trimming, spacing, and plant nutrition are all key ingredients, as well.

Challenges Remain

Mark Brotherton at SePRO Corporation says that, for the most part, growers have mastered the art of PGRs, although there can be a few struggles at times.

“Probably the most common challenge is flower delay,” Brotherton says. “In certain instances, PGR sprays can impact bud development and flower timing.”

Brotherton says in many cases, drench applications can reduce the amount of delay that may occur, or growers can use PGRs that will have less impact on flowering.

“Another challenge I commonly hear about is even growth regulation in mixed baskets,” Brotherton says. “Often, the different species in a basket will respond differently to PGRs. The best approach is to make a PGR application to the plug/liner before it is transplanted. This way, you can adequately dose each species individually. If necessary, near the end of production, low rates can be sprayed over the top to help maintain proper size.”

One aspect Brotherton says SePRO is exploring further is micro drenching.

“It’s not a new concept, but one I think can really benefit growers,” Brotherton says. “Through frequent applications at very low rates, micro drenches can result in a more toned and uniform plant. It also gives the grower greater flexibility during production when things are constantly changing. Topflor has shown to work very well utilizing this strategy.”GG

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