New plant growth regulator research website

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Controlling stem extension of greenhouse crops can be a challenge on naturally tall crops. To manage plant height, growers often apply various plant growth retarding chemicals as well as utilize nonchemical strategies such as infrequent irrigation or a temperature drop in the early morning. Over the past 15-plus years, researchers in the floriculture group at Michigan State University have performed dozens of experiments with chemical plant growth regulators (PGRs) to evaluate their effectiveness at suppressing stem extension on greenhouse crops. The results for many species have been published in trade magazines and refereed journals and presented at various conferences.

A new MSU floriculture web page,, has been developed to provide a summary of research results from many of these PGR trials. The information presented is limited to research performed at MSU and includes PGR responses for both herbaceous perennials and annual bedding plants. Visitors to the web page can select a species from a drop-down menu and then one or more photographs are displayed that demonstrate the PGR responses. 

The web page does not provide recommended products or application rates; rather, it is intended to serve as a guideline to help growers determine whether a PGR is effective on a particular species. A summary table is also provided that lists the commercially available PGRs commonly used on greenhouse crops and their active ingredients. In most cases, we would expect similar responses among products containing the same active ingredient.

We hope that this web page will be a valuable resource for greenhouse growers when making PGR application decisions. As with all growth regulators, we recommend that growers perform their own trials on a small scale to determine appropriate rates given the species and cultivar, desired response, and environmental conditions. As additional research is performed at MSU on PGRs, this web page will be updated to provide growers with the most recent research-based information. We welcome your feedback on this new grower tool. For more information, please visit the MSU PGR research web site at:

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