2018 ASHS Annual Conference

One of many strategies available to limit the potential for future plant invasions is to introduce and promote the use of regionally native taxa for horticulture. As various honeysuckles (Lonicera spp.) of Eurasian origin have proven to be invasive outside their native ranges, we evaluated methods to propagate a potential North American alternative, mountain fly honeysuckle (Lonicera caerulea var. villosa). This species of northern climates has low population densities through much of its native range, and seems ineffective at displacing other species. Nonetheless, our observations of this plant in horticultural landscapes suggest that it could be used in landscapes more varied than its native distribution implies. To conduct propagation trials, we collected softwood terminal stem cuttings from plants indigenous to Maine in June 2017, treated each with one of several concentrations of potassium salt of indole-3-butyric acid (K-IBA), and stuck them into media with different proportions of perlite and milled peat moss. We conducted two separate experiments to independently evaluate the suitability of overhead mist or subirrigation during rooting. The percentage of cuttings that rooted was high and not significantly affected by treatments. Root dry weight, as well as root volume and number of root tips measured by scanning fresh roots and analyzing the images using WinRHIZO software, increased with concentration of applied K-IBA and proportion of perlite in the substrate. Within each system, K-IBA application rates from 8,000 to 12,000 mg·L^-1 and a porous mineral substrate produced well rooted cuttings with the high success rate necessary for commercial propagation. Our results illustrate that a simple subirrigation approach to cutting water management can produce quality rooted cuttings of mountain fly honeysuckle when overhead mist is not available. Moreover, a residential landscape trial that we initiated in August 2016 confirms that this North American member of the circumboreal species complex can establish and grow in a mesic and predominantly mineral soil, despite its tendency to persist in peat wetlands throughout much of its range. Rooted cuttings planted in a landscape soil in Maine established readily and produced annual shoot elongation on par with the more robust natural populations observed, and far exceeding the several centimeters of growth we often observe among mountain fly honeysuckles indigenous to bogs and fens in New England.