PGRs for the potted

Greenhouse growers striving to meet the demands of increasingly savvy and discerning consumers know they need to pull out all the stops to meet that demand. This has never been more apparent than with the production of potted bulbs for the holidays and other occasions, when consumers are looking for eye-appealing products with long shelf lives. Growers of potted bulbs can meet consumer expectations, in part, by doing everything right from planting to finish in the greenhouse, including increased spacing and specific cultural growing conditions. Still, most greenhouse growers, pressed for space and time, need to rely on plant growth regulators (PGRs) to control flower stem elongation during and after greenhouse production.

Greenhouse growers have a wide choice of PGRs to choose from. The difficulty comes not only in matching the product to the genus of plants, but specific cultivars, according to David Barcell, senior technical manager for OHP, which provides pesticide and PGR products for greenhouse and nursery production. Here are some PGR advancements that will help growers meet their growing objectives.
 

Daffodils and hyacinths

Growers experience fewer problems with stem elongation during production of potted plants such as tulips and hyacinths than a grower of bedding plants might experience with petunias. However, it’s a little more difficult to control growth once the plants leave the cushy confines of the greenhouse.

“The issue is height control, which in many cases is more needed for post-harvest growth control,” says William Miller, professor in the Horticulture Department at Cornell University. “Once they go into a retail situation in the stores they may stretch. We try to keep post-harvest stretch to a minimum with certain plant growth regulators” he explains.

Miller and his team at Cornell have come up with a number of solutions for different potted plants with more likely on the horizon.

Potted daffodils (Narcissus) and hyacinths (Hyacinthus), sold in garden centers and retail outlets to consumers who just can’t wait for spring, are examples of two crops that can suffer from stem elongation after harvest.

One of the latest things they’ve been working on at Cornell with these plants is using Florel and Collate as a soil drench instead of a foliar spray to control stem growth. Miller says it’s not labeled for such use yet but expects it will be.

“It’s very, very interesting,” says Miller of the research. “There will be possibilities to use it with spray booms.” He said they haven’t experimented with it on tulips “yet,” but expects they will as they learn more about it during this year’s growing season.
 

Controlling stem height in amaryllis

Amaryllis (Hippeastrum) is known for its tall, stately stems and brassy flowers that bring a welcome respite from the drabness of winter and is also marketed for major holidays, including Mother’s Day, Thanksgiving, and Christmas. The long stems on amaryllis are a little difficult to grow with uniformity, regardless of how well they’ve been tended to in the greenhouse. PGRs are needed to help ensure a uniform growth rate which ultimately makes the plants more marketable. Researchers at Cornell, in collaboration with Kansas State University, have been looking at using PGRs with amaryllis, something that hasn’t been explored much heretofore.

In short, pre-plant bulb soaks at 100 ppm for at least 60 minutes were effective in reducing flower stem height in amaryllis. Higher concentrations didn’t result in greater flower stem height control. The PGRs used were cultivar specific, with Piccolo and Topflor “slightly” more effective than Sumagic at controlling flower stem height in ‘Black Pearl,’ amaryllis, while no differences were found with the cultivar ‘Pamela.’ They also found that soaks longer than 60 minutes caused a three- to nine-day delay in flowering for several treatments they performed. Researchers believed the difference could affect marketing of amaryllis, which has a short shelf life and a specific harvest target date. In conclusion, PGRs were found by the researchers to be “variable” between and even within cultivars of amaryllis.
 

Researching Calla lilies

Calla lilies (Zantedeschia) are popular among consumers and are used as wedding bouquets. Interest continues to increase for both pot and cut flower production of callas ( C. Miller and W. Miller). As with other potted plants normal growing conditions or “best practices” are only part of the picture in growing marketable calla lilies.

Researchers at Cornell University have honed in on two products that work well in controlling stem length with different specific cultivars of callas when used in moderation. In studies they found flurprimida (Toplor, Sepro) and paclobutrazol (Bonzi, Syngenta) to control plant height when used as a drench, which appears to be the best way to apply this PGR. (For more information on rates for specific calla lily cultivars can be obtained at www.flowerbulbs.cornel.edu.
 

Extending Easter lilies

Growers will see 20-25% longer bloom time with Easter lilies by using a product they’ve tested at Cornell, called Fascination, according to Miller. Growers can also expect less leaf yellowing by using this product, which is a mixture of phenylmethyl and gibberellins GA4 and GA7.

Fascination is also labeled for use on potted hybrid and Asiatic lilies. Height control can also be controlled using Sumagic at less than five parts per million and with Topflor drenches.

Controlling dahlias

Growing dahlia plants for large pot plant use is best accomplished via the propagation of the tuberous roots, as opposed to growing by vegetative means or from seed. Dahlias, which are not winter hardy in the colder northern climates are nevertheless popular with gardeners around the country.

Dahlia tuberous roots are field-grown in Holland and harvested in late fall/early winter for export. Roots are planted in a minimum 6-inch pot, with one root per pot. Growers using PGRs for controlling the growth of potted dahlias should plant the crown of the bulb and its buds slightly above the growing medium, allowing enough space above the soil for an application of a PGR drench (W. Miller and C. Filios).

Growth regulation is a major concern for potted dahlia production (W. Miller and C. Filios). Soil drenches using A-Rest (ancymidol) have been the standard for many years. Drenches are applied 10-14 days after planting. According to researchers at Cornell, A-Rest has been effective, but costly at 17-25 cents per milligram. At that rate, it could cost up to $.50 per pot to grow dahlias, according to the researchers.

Bonzi and Topflor may offer better growth control at a lower cost than A-Rest. For example, studies from North Carolina State looked at the use of Sumagic, Bonzi and Topflor on dahlias. Using the cultivar, ‘Red Pygmy’ (a dwarf cultivar), they found that short plants, that is 6 to 7 inches above the rim of the pot, were produced with 0.5 to 1mg A-Rest. With Bonzi, “visually appealing” plants were produced with 1 to 2 mg drenches, and with Sumagic the team produced good looking plants at only 0.125 to 0.25 mg per plant.

As they say in a stock fund prospectus, past performance doesn’t guarantee future results, so it is best to try out these and other PGRs on a test crop before treating an entire crop. Also, be aware that growing conditions vary according to your particular locale and weather conditions; adjust your PGR regimen accordingly.

“Talk to the guys who have done it before, because everybody’s growing environment is different,” asserts 40-year veteran grower John Tomasovic, Jr., vice president of Tomasovic Greenhouse and Nursery in St. Louis, Mo.
 

Best practices

The use of PGRs for controlling growth during greenhouse production and beyond assumes that growers have tried all other methods of producing a marketable crop. These methods or practices include proper cultivar selection and carefully monitoring temperature, light quality and intensity, watering, spacing, and fertilizing practices.

The decision to use a PGR on a specific cultivar should be made after considerable research. Like using a new cleaning product on expensive furniture, it is advisable to test a small sample crop with the PGR of your choice to see how it is going to work before treating an entire crop. Maintain detailed records of PGR applications and accompanying growing practices.
 

PGRs and the environment

Plant growth regulators are generally safe to use, asserts Miller. Of course, that’s assuming you follow the recommendations in the labeling. Most companies who sell these products, conspicuously post Material Safety Data Sheets (MSDS) on their websites, making it convenient for growers to easily see the active ingredients in each product, what is recommended for personal safety equipment (PPE), and any concerns for the environment. Miller says that PGRs are generally used at “substantially” lower rates than insecticides making them a pretty safe bet for you, your employees, and the environment, assuming all labeling is strictly adhered to.

Neil Moran is a horticulturist and freelance writer based in Sault Ste. Marie, Mich.

• For more on PGRs for potted plants, www.flowerbulbs.cornell.com
• Holland Bulb Forcer’s Guide, by August A. DeHertogh.
• Mobile app for mixing PGRs: PGR Mix Master, developed by the University of New Hampshire, is available for iPhone, Android, and Blackberry users. It calculates PGR mixing rates for sprays and drenches for most of the common chemicals available for ornamentals, according to the maker.
  http://bit.ly/1aEE2pu