Plant growth regulators can perform a number of tasks in your perennials production program. In a market where calls for compact plants are increasing, however, height control can be achieved with the right formulation.

If you grow perennials in containers, you’re aware of the market demands for uniform growth. In production settings, as well as in retail locations, herbaceous perennials grown in pots tend to stretch and become leggy or simply overgrow their pots before their scheduled market date. These plants are less marketable and harder to maintain. Many growers resort to pruning, which is not only costly in terms of labor, but also delays plant production for two to four weeks.

Enter plant growth regulators.

Choosing the correct PGR

For best results, PGRs should be handled as production tools – like water and fertilizer. They should not be used as crutches for poor management of other cultural practices. PGRs should be an integrated part of your crop production cycle.

The selection of PGRs and their application rates will be affected by how your crop is grown. Especially with very vigorous plants, as many of the herbaceous perennials are, higher fertility and irrigation levels will increase the amounts of growth regulator required to prevent excessive growth. Shading, lower light levels or tight plant spacing – especially under higher growing temperatures – will also increase plant stretch and reduce lateral branching.

For the highest quality plants, the use of PGRs must be integrated into your production plan. PGRs are most effective when applied at the appropriate times to regulate plant growth or development. In other words, growth retardants cannot shrink an overgrown plant. They must be applied before the plant is overgrown to avoid plant stretch. When planning PGRs in your production schedule, consider what you want to accomplish with the treatment.

  • Do you want to regulate shoot growth of the plant, resulting in a sturdier, more compact plant with improved color? If so, you probably want a growth retardant.
  • Do you want to increase plant branching for enhanced cutting production, or for a bushier potted plant or hanging basket? If so, you probably want to use a branching agent or “chemical pincher.”
  • Do you want to enhance flower initiation or synchronize flowering? If so, you probably want to use chlormequat chloride or gibberellic acid.
  • Do you want to remove flowers from stock plants to increase the number of vegetative cuttings? If so, you probably want to use an ethylene generating compound.

Answering these questions will indicate what type of PGR you need to use to accomplish your goal and the most appropriate timing of the application. Then you will need to select a specific PGR in that class and determine the appropriate dosage and application method to attain the desired response.

Often your goal is to reduce the height of perennial stock to facilitate shipping and distribution. With that in mind, we offer the following information in an easy-to-use table format (Click to download PDF). (Mention of specific product names does not imply an endorsement.)

Joyce G. Latimer, Ph.D., is a professor in the Department of Horticulture at Virginia Tech, Blacksburg, Va., and extension specialist for greenhouse crops for Virginia. She can be reached at Holly Scoggins, Ph.D., is an associate professor in the Department of Horticulture, and is director of the Hahn Horticulture Garden on the Virginia Tech campus. She can be reached at