Increasing chrysanthemum height

Crops shorter than desired can benefit from a plant growth regulator application – learn about key considerations.

Chrysanthemums in flower at desired heights for their container sizes.
Chrysanthemums in flower at desired heights for their container sizes.

Some fall chrysanthemum growers have reported relatively short crops this year (see photo). Whether crops are growing outside or in greenhouses, one of the most effective ways of increasing plant height is to apply a plant growth regulator that includes gibberellic acid (GA). The two most common GA products used on floriculture crops are Fascination by Valent Professional Products (download Fascination label and MSDS) and Fresco by Fine Americas (download Fresco label and MSDS). Both of these products contain 1.8 percent GA plus another plant hormone, benzyl adenine (BA). However, other products that contain GA can also be effective.

Fascination and Fresco are typically applied as foliar sprays, but a few years ago some growers and industry experts reported desirable responses with drench applications. In at least some instances, growers who reported positive drench results delivered their applications using a boom, which meant that the drench was a combination of a spray and drench. However, more recently, some growers have delivered substrate drenches without contact with the foliage and reported a promotion of extension growth. Therefore, both foliar and drench applications can produce desired results, although drench applications would cost roughly 10 times that of a spray since more volume of solution is required.

Michigan State University Extension offers the following keys considerations to successfully use Fascination or Fresco on chrysanthemum:

  • For sprays, ensure thorough canopy coverage; consider using a higher volume than usual, for example 3 quarts per 100 square feet. Add a surfactant to ensure good contact with stems.
  • Apply as early as possible; earlier applications have more potential to increase stem elongation than applications late in the crop cycle.
  • For sprays, consider starting at 2 to 4 ppm, depending on desired responses and stage of development (late stages may require the higher rate). In addition, make foliar applications during periods of slow drying conditions, such as early in the morning or on a calm, cloudy day.
  • For drenches, start at 5 to 10 ppm using a standard drench volume; for example, 4 ounces per 6-inch pot.

Fascination and Fresco are normally effective for seven to 10 days, after which there is little or no stimulation of stem elongation. If a second application is needed, wait at least seven to 10 days since it takes time for the effects of the first application to show results. Finally, ensure plants are not stressed or too dry with a foliar application. Read the product labels for additional information including user safety recommendations. In addition, conduct your own trials on a small scale to determine appropriate rates and application methods for your growing conditions and desired responses.

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

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