Asexual Propagation of Forestiera pubescens (Nutt.) Using Stem Cuttings

Desert olive (Forestiera pubescens), a large shrub or small tree native to the southwestern United States, exhibits ornamental value and has potential for broader application in managed landscapes. F. pubescens exhibits drought and flood tolerance making it well suited for use in urban settings and in green infrastructure, which experience variable, and often extreme, conditions. This taxon has demonstrated cold hardiness in US Department of Agriculture (USDA) zone 4b and may be useful as an option for the diversification of landscapes in the Upper Midwest. However, asexual propagation protocols for producing this taxon are nonexistent. If this species is to be adopted by the nursery trade and produced at a large scale, then propagation protocols need to be developed. The objective of this study was to investigate methods for asexual propagation of F. pubescens and explore the factors that influence rooting for different types of stem cuttings. We examined the rooting of F. pubescens when propagated using softwood, semihardwood, or dormant hardwood stem cuttings. Semihardwood cuttings were treated with varying concentrations of indole-3-butyric acid (IBA) or left nontreated to evaluate the effects of IBA on rooting. Rooting percentage, root length, and number of roots were evaluated. After 35 days under intermittent mist, 21%, 62%, 74%, and 87% rooting occurred with the nontreated controls [95% ethyl alcohol (ETOH)], 1000, 2000, and 3000 ppm IBA, respectively. Dormant hardwood cuttings were not a viable technique for propagating this taxon. Semihardwood cuttings placed in a 100% perlite substrate resulted in 97% rooting, whereas the use of a 50/50 peat/perlite substrate yielded 40% rooting. Results confirm that F. pubescens can be successfully propagated using stem cuttings. Cultivar specificity was determined to play a central role in the rooting response of this species. The application of IBA was not necessary for rooting to take place; however, the number of roots and root length were improved by treatment with IBA. Our findings support the use of semihardwood or softwood stem cuttings in 100% perlite substrate with an application of 3000 ppm IBA to achieve optimal rooting of F. pubescens.