By Joyce Latimer, Virginia Tech
Growers are always looking for better ways to overwinter perennials, ways to get higher survival rates and better quality from overwintered plants. We all know that many factors affect those results – stage of growth or development, water status, fertility status, disease pressure and incidence and just plain weather! What about PGRs?
In this blog, I want to share the results of a couple of studies we have conducted with PGRs on overwintering perennials. Note: these studies have not been repeated multiple times. Winter weather conditions were not extreme in either year.
Growth Retardants – Concise or Piccolo 10 X.
Herbaceous perennials, Gaillardia ‘Gallo Peach,’ Heuchera ‘Brownie’ and ‘Pistache,’ and Echinacea ‘Hot Papaya’ and ‘Milkshake,’ were planted in early August. Two weeks later the first of two foliar sprays of Concise at 15 ppm or Piccolo 10 XC at 80 ppm was applied. The second application was made 2 weeks after the first. Growth was assessed at 5 weeks after the first growth retardant application and compared to untreated controls. The growth regulators reduced growth moderately in all crops with the height of treated Echinacea plants measured at 25% to 35% less than that of control plants (Photo 1). Plants were overwintered in an unheated cold frame. In addition, plants were covered with two layers of row cover (Remay) when temperatures were projected to be below 20⁰F at night. Overwintering survival was assessed the following spring.
Winter survival rates were nearly 100% in all of these crops. However, there were some carryover effects of the growth retardants. Percent of plants flowering tended to be less than that of untreated plants for Gaillardia plants treated with Piccolo 10 XC while flowering of Gaillardia plants treated with Concise tended to be greater than with controls. Quality ratings of all plants were very high. Heuchera ‘Pistache’ plants treated with Concise or Piccolo the previous fall had less plant diameter after overwintering than untreated plants even though height was unaffected. In contrast, plant diameter of H. ‘Brownies’ was greatest in plants treated with Concise the previous fall. After overwintering, Echinacea ‘Hot Papaya’ plants previously treated with Piccolo 10 XC were shorter, had less shoot dry weight and a slightly lower quality rating than the untreated or Concise-treated plants (Photo 2). Echinacea ‘Milkshake’ plants previously treated with either growth retardant were not shorter than untreated control plants but had less shoot dry weight. Flowering and plant quality were very high.
Branching Agent – Configure
In the study described above, we also included a treatment of 600 ppm Configure applied twice as described above. Configure had no effect on survival, branching or growth of any of those crops after overwintering with one exception. Echinacea ‘Milkshake’ plants previously treated with Configure at 600 ppm tended to have a greater number of basal breaks than untreated control plants [control 8.1 vs. Configure 12.6] after overwintering.
Prior to the study above, we evaluated the effect of Configure applied once about two weeks after fall planting on survival and branching of three cultivars of Echinacea, Double Decker, White Swan and Magnus, using the same overwintering protection described above. Configure had no consistent effect on winter survival of Echinacea (Table 1). Although there was no improvement in survival of ‘Double Decker,’ there was a slight improvement, relative to control plants, in ‘White Swan’ and ‘Magnus.’ Survival rates were based on 20 to 40 plants per cultivar. As expected, Configure increased branching of all cultivars in the fall after application. However, in all cultivars the following spring, branching was also greater with plants previously treated with Configure (Table 1).
Plant growth regulators are showing no harm to herbaceous perennial plants being overwintered in containers. Higher rates of PGRs may result in carryover growth regulation the following spring which may be beneficial if the rates are fine-tuned. PGRs also offer no consistent improvements in plant survival or growth – with the possible exception of improved branching of Configured-treated Echinacea.