Overhead mist revolutionized the propagation industry by providing a reliable means to manage transpirational water loss by leafy stem cuttings. This system slows transpiration of cuttings primarily by decreasing leaf temperatures through evaporative cooling from the leaf surface (Hartmann et al., 2011). However, overhead mist has potential drawbacks, including the use of large volumes of water, potentially unsanitary conditions created by persistent water films on leaves (Preece, 2003), the depression of root-zone temperatures by evaporative cooling (Hartmann et al., 2011), nonuniform misting coverage, leaching of foliar nutrients (Preece, 2003), and the need to extensively acclimate cuttings to a low-humidity, mist-free environment.
A potential alternative to overhead mist is submist aeroponics, which relies on the application of mist from below the cutting, to the base of the stem inserted into an enclosed chamber. Several systems are available on the consumer market for use by home gardeners, but their potential for propagation of woody ornamental plants has not been well researched. Recently, Peterson et al. (2018) found that submist aeroponics was superior to overhead mist for the propagation of ‘Wizard Mix’ coleus (Plectranthus scutellarioides) by stem cuttings. Coleus rooted in submist systems produced more than three times as many primary roots, with maximum root lengths six times greater, and root dry weights eight times those of cuttings propagated in overhead mist systems (Peterson et al., 2018). To build upon on these findings, we sought to test submist systems as alternatives to overhead mist for the propagation of woody ornamental plants by stem cuttings.
Korean lilac and inkberry are two species grown commercially in the nursery industry. According to Dirr and Heuser (2006), korean lilac can be propagated reliably from softwood stem cuttings treated with 8000 mg·L−1 indole-3-butyric acid (IBA). Although they do not specify a substrate for this species, Dirr and Heuser (2006) suggest perlite as a suitable rooting medium for common lilac (Syringa vulgaris). Inkberry can be propagated from semihardwood cuttings during late summer and fall, for which Dirr and Heuser (2006) suggest 1000–8000 mg·L−1 IBA and the use of a 50:50 (by vol) peat:perlite substrate.
Our objective was to test the feasibility of submist aeroponics as an alternative to overhead mist for propagation of woody plants by stem cuttings. We conducted separate experiments with korean lilac and inkberry to determine whether measures of rooting differed between the two systems. For korean lilac, we also investigated whether the plants from each system transplanted successfully into a soilless medium and produced additional root biomass.
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