The primary objectives of this research are to analyze the effects plant growth regulators and pinching practices have on the growth habit of Penstemon x mexicali Pikes Peak Purple and Red Rocks and to produce more marketable containerized Penstemon. A preliminary study analyzed the effects branching agent PGRs had on Pikes Peak Purple. We found that the PGRs benzyladenine and ethephon were successful at producing more branches than the untreated control when the plants were considered finished in the container. Another group of PGRs known as growth retardants were also evaluated on Pikes Peak Purple. Both high and low rates of foliar applications of paclobutrazol or uniconazole resulted in growth control of the crop. Liner drench or soak applications of paclobutrazol were the most effective at reducing growth but resulted in over-regulated and stunted plants. A separate study focused on the combination of branching agents and pinching practices on Pikes Peak Purple. Both pinching and the application of branching agents improved overall plant quality until the stage of flower initiation where further growth regulation was needed. Based on the results of the previous experiments, we conducted a study combining branching agents and growth retardants on Pikes Peak Purple and Red Rocks. We found that the most marketable Pikes Peak Purple plants were produced with one pinch during the liner stage, two applications of benzyladenine, and one drench application of paclobutrazol. The most marketable Red Rocks plants were produced with one pinch during the liner stage, and two applications of ethephon. / Master of Science

The objective of this study is to evaluate the efficacy of PGRs to improve branching during production of herbaceous perennial liners and finished plants. The effects of benzyladenine (BA) on the branching and root and shoot growth of Agastache Clayt. Ex Gronov. 'Purple Haze', Gaura lindheimeri Engelm. & A. Gray 'Siskiyou Pink', Lavandula × intermedia Emeric ex Loisel. 'Provence', Leucanthemum × superbum (Bergmans ex J.W. Ingram) Bergmans ex Kent. 'Snowcap', and Salvia × sylvestris L. (pro sp.) 'May Night' was tested. Root dry weight was found to be highly correlated to root volume and root surface area. In liners, all taxa except Salvia had increased branching while all except Gaura had reduced rooting. Increased branching was not evident in most taxa as finished plants. The effects of BA on Aster 'Professor Anton Kippenberg' (Symphyotrichum novi-belgii L.'Professor Anton Kippenburg'), Campanula punctata Lam. 'Cherry Bells,' Cosmos atrosanguineus (Hook) Voss., Verbena bonariensis L. 'Lollipop,' Rosmarinus officinalis L.'Hill Hardy' and Veronica spicata L. 'Goodness Grows.' was tested. BA increased branching of three taxa as liners while roots were not affected. The addition of IBA did not improve root growth in BA-treated plants. Dikegulac sodium and ethephon were evaluated as branching enhancers in the same six perennials. Dikegulac increased branching of all except Campanula while ethephon increased branching in Veronica and Verbena. The effects of application time of BA on the branching of Agastache Clayton ex Gronov. 'Tutti Frutti' and Verbena bonariensis 'Lollipop' was evaluated with application of BA at 0, 7, 14, 17, 20 and 21 days after sticking (DAS); however growth was reduced in plants treated before rooting had occurred. Agastache finished plants treated at 14 DAS had increased branching whereas branching was not affected in Verbena liners or finished plants. The effects of single or multiple applications of BA and dikegulac sodium on Sedum spectabile Boreau 'Autumn Joy,' Gaillardia aristata Pursh 'Gallo Red,' Phlox paniculata L. 'Bright Eyes,' Nepeta racemosa Lam. 'Walker's Low,' Delosperma NE Br. 'Table Mountain,' and Achillea L. 'Moonshine' were evaluated. Two applications of PGR was most effective at increasing branching in finished plants. High rates of dikegulac sodium reduced growth in most plants studied while BA increased branches without negatively affecting plant growth. / Master of Science