Regulation of Growth and Branching of Containerized Penstemon x mexicali Cultivars

Abstract

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.