A wide variety of ornamental crops are treated with plant growth retardants, which are chemicals that inhibit extension growth. There is a wide range of growth-retarding products that are registered for use, with efficacy depending on a number of factors including the product, crop, concentration and volume of application, and environmental conditions. Unfortunately, over-applications of plant growth retardants happen, usually because the concentrations were too high.

Following an over-application, plant growth usually slows or stops for an extended period of time and flowering is often delayed. Probably the best way to treat a crop that has been over-regulated with a growth retardant is to apply a product that contains gibberellic acid, such as Fascination (Valent Professional Products) or Fresco (Fine Americas). Both products also contain an equal amount of the benzyl adenine.

The label for Fresco was recently updated to include guidelines on how to promote growth on ornamentals, including bedding plants, perennials and bulb crops. The recommendation, available online, is applicable only to growers in Michigan. According to the label, growers should start with a spray application of 1 ppm. This may be effective on some crops, but others may need a higher concentration (3 to 5 ppm) to obtain the desired response. Importantly, growers are cautioned to wait at least five days, and preferably at least a week, before a second application.

For more information on growth regulators, including Fresco and Fascination, visit this MSU Floriculture website.

Dr. Runkle’s work is funded in part by MSU’s AgBioResearch.