Plant Growth Regulators to Control Growth of Containerized Abelia

Colorful woody plants normally grown as landscape plants have potential for use in containers.  One such plant is Abelia ×grandiflora, a popular flowering shrub that is drought and heat tolerant, and pest resistant.  In order to produce a marketable well-filled container, plants need to exhibit balanced growth with multiple branches and symmetry, and colorful foliage or heavy early flowering.  Despite their inherent potential, most abelia benefit from pruning to develop a compact, well-branched form.  Manual labor for pruning increases production costs.  Plant growth regulators are an effective way to achieve growth control, reduce production costs and produce a marketable plant. Abelia genotypes with colorful foliage or early blooming were selected from a plant breeding program at the University of Georgia to evaluate the efficacy of growth regulators to develop desirable form in containers.  In 2007, three genotypes were given foliar sprays of the gibberelin inhibitor paclobutrazol (Bonzi, 0.4%) at 0, 30, 40 and 50 mg/L.  Foliage of another three genotypes was sprayed with a branching agent dikegulac-sodium (Atrimmec, 18.4%) at 0, 30, 40 or 50 mg/L.  Growth and flowering data were collected after three weeks, and plants of all six genotypes were then drenched with 0, 30, 40, or 50 mg/L of paclobutrazol.  Data was again collected three weeks later.  Results showed that with two treatments of paclobutrazol, height and width of all genotypes was reduced.  Genotypes treated with Atrimmec exhibited increased branching.  In 2008, foliage of five genotypes was sprayed with cyclanilide at 0, 25, 50, 75, or 100 mg/L.  After about five weeks, growth data was collected.  Although some genotypic differences were observed, in general, cyclanilide-treated plants had reduced height, growth index, and internode length and increased shoot number.  Effect on earliness of blooming was mixed.  These results demonstrate that plant growth regulators are effective in controlling growth of abelia in containers and are helpful to produce attractive plants for spring sales.