Effects of Substrate Drenches Containing Ethephon on Containerized Annual Bedding Plants are Affected by Concentration and Application Timing

Ethephon is a plant growth regulator that has several effects on flowering ornamental plants, including delayed flowering, enhanced lateral branching, and suppression of stem elongation. Traditionally, ethephon has been applied to plants using foliar sprays. However, recent research has shown that applying ethephon with substrate drenches can elicit the same suite of responses observed when applied in foliar sprays. However, there are no data on how concentration and application timing affect the efficacy of substrate drenches containing ethephon. Our objectives were to quantify the effects of ethephon concentration, timing of substrate drench application, and their interaction on the growth, size, and flowering of annual bedding plants. Angelonia (Angelonia angustifolia Benth.), geranium (Pelargonium ×hortorum L.H. Bailey), and vinca [Catharanthus roseus (L.) G. Don.] seedlings were planted in 4-inch diameter round containers filled with a commercial, soilless growing substrate comprised of sphagnum peat moss and perlite. Zero, 5, 10, 15, or 20 days after planting seedlings, 70-mL aliquots containing 0, 50, 100, or 200 ppm ethephon were applied to the surface of the substrate. The date the first flower opened, height of the plant from the surface of the growing substrate to the top of the plant canopy and the widths at the widest point of the plant and perpendicular from that widest point were recorded for each individual plant and time to flower was calculated. Species varied in their growth and flowering responses to ethephon concentration, drench application timing, and their interaction. When 100 or 200 ppm ethephon drenches were applied 0 d after planting, plants remained in visible bud, while applications at 20 d after planting had minimal effect on flowering for angelonia and geranium. Width of geranium was only affected by ethephon concentration, not application timing. Alternatively, ethephon and application timing interacted to affect the width of angelonia and vinca; plant widths were suppressed with ethephon concentration 0 d after planting yet minimal effect was observed when applications were made 20 d after planting. Shoot and root dry mass and height of all three species were affected similarly, with early ethephon applications made immediately after planting have a greater impact than later applications. Ethephon drenches are effective in controlling the height and width of containerized floriculture crops. However, based on our the results of our research, the application timing of substrate drenches should be determined based on the desired effects and the concentration of the solution.