Horticulturists who design informal landscapes may broaden their plant palettes by selecting species indigenous to local floras. Many native, colony-forming shrubs might be useful for horticultural landscapes but are absent from the nursery industry. Three examples from northern climates of North America are sweetgale (Myrica gale), rhodora (Rhododendron canadense), and catberry (Ilex mucronata). Sweetgale is a short-statured and densely branched shrub with finely textured, fragrant foliage. Rhodora produces attractive pink to purple spring flowers followed by steely blue-green foliage held on a mound of stiff branches through summer before developing autumnal coloration in tones of rose, orange, and burgundy. Catberry develops attractive and densely branched canopies and produces distinctive matte red fruits on elongated pedicels in late summer.
Many native shrubs have proven amenable to asexual propagation (Cartabiano and Lubell, 2013) and could therefore be more widely produced in the industry, whereas others like eastern leatherwood (Dirca palustris) are recalcitrant and unlikely to reach even those consumers keenly interested in native plants (Norris, 2011). Recently, the prospects for greater commercialization of a popular native plant of the northeastern United States, sweetfern (Comptonia peregrina), have been increased by improved methods to propagate it commercially (Gardner et al., 2019; Lubell and Brand, 2011). Phenology is an important factor for some species, such as species of serviceberry (Amelanchier sp.), which may be propagated from softwood cuttings but are famously recalcitrant once terminal buds have set (Still and Zanon, 1991). Species also may respond differently to environmental factors like the concentration of applied auxin (Cartabiano and Lubell, 2013) or the physical composition of the rooting medium (Hayes and Peterson, 2019; Lubell and Brand, 2011).
The first steps to wider adoption of new plants for horticulture are to develop effective protocols for their propagation and identify niches they can fill in horticultural landscapes. To evaluate methods for the efficient propagation of sweetgale, rhodora, and catberry, we conducted experiments over 2 years on the effects of cutting collection date, substrate composition, wounding, and the concentration of applied potassium salt of K-IBA on rooting percentage and metrics of root system quality.
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