Expected Morphological Effects of the Plant Growth Regulator Trimtect® on Landscape Shrubs Takes Time and Varies by Species

Abstract

Gibberellic acid is a naturally occurring plant hormone that regulates growth such as stem elongation and germination. Paclobutrazol is a synthetic growth regulator that inhibits the formation of gibberellic acid resulting in altered growth. Trimtect, a formulation incorporating paclobutrazol, is used commercially and sprayed on the foliage of on landscape plants to sustain desired growth forms and reduce maintenance. Studies have shown that paclobutrazol applications lead to reduced internode length, leaf area, and overall plant height in several woody species. Chlorophyll, a leaf pigment, has also been seen to increase in response to paclobutrazol application in many species. Rainbow Treecare Scientific Advancements (Minneapolis, MN), the manufacturers of Trimtect, partnered with our Plant Form and Function class to research Trimtect’s effects on the morphology of three common landscaping shrub species (Hydrangea macrophylla, Buxus sinica, and Rhus aromatica). It was our objective to determine the morphology altering properties of Trimtect to provide empirical evidence for Rainbow Treecare Scientific Advancements to develop new formulations and improve guidelines for commercial use.