Stem cuttings are traditionally propagated using overhead mist systems. Recent work has explored the use of a different approach: submist propagation (Peterson et al., 2018a, 2018b; Sanchez et al., 2020). Submist propagation systems apply water to the basal portions of cutting stems, rather than overhead. Cuttings are suspended in an enclosure that contains a manifold of mist nozzles. Plants propagated in this system may have superior rooting compared with those propagated in overhead mist (Peterson et al., 2018a, 2018b; Sanchez et al., 2020). After propagation, cuttings are transplanted into soilless media, and their growth is similar to that of plants propagated in overhead mist (Peterson et al., 2018a, 2018b).
Submist propagation systems were introduced in 1964 at the International Plant Propagators’ Society Western Region annual meeting (Nitsch, 1964). They have been used experimentally to propagate semihardwood cuttings of peach [Prunus persica (Coston et al., 1983)]. Submist propagation systems are a relatively new concept in commercial operations. Previous research with these systems has been conducted on small-scale, custom-built submist units that are unsuited to commercial propagation because they hold few cuttings (Peterson et al., 2018a, 2018b; Sanchez et al., 2020). For the industry to adopt submist propagation, larger systems must be designed that can effectively hold the greater number of cuttings propagated at commercial greenhouses or nurseries.
One potential benefit of submist systems for propagation, compared with overhead mist, is that submist systems potentially use less water. This is because the enclosed system recycles water and reduces water losses to evaporation. Although we are unaware of research quantifying the amount of water used during overhead mist propagation, a survey of greenhouse growers indicated that 4.5 to 46.1 L·m–2 of leachate is produced over 4 weeks (Santos et al., 2008). Peterson et al. (2018b) found that submist systems used about the same amount of water for the entire time needed to propagate coleus (Plectranthus scutellarioides) as an overhead mist nozzle used in 30 s. Techniques for reducing water use during propagation without impacting rooting negatively would help growers reduce their overall water usage.
Another potential benefit of using submist for propagation is that it may improve root development on some woody and herbaceous perennials that are challenging to propagate or that form roots slowly. In previous research, manchurian lilac (Syringa pubescens ssp. patula ‘Miss Kim’) had more roots and longer roots when it was propagated in submist (Sanchez et al., 2020). Manchurian lilac plants are often challenging to propagate if cuttings are not taken at the right time (Hartmann et al., 2002). A broader variety of species, including difficult-to-root plants, should be tested in submist propagation systems to determine whether these challenging species form roots more reliably or quickly in submist. For example, sweetfern (Comptonia peregrina) is challenging to propagate from stem cuttings. Although some growers propagate sweetfern from rhizomes, the technique is slow and it limits the number of plants available (Griffith Gardner et al., 2019). Blue star flower (Amsonia tabernaemontana) is propagated from seed or by stem cuttings, which often form roots slowly (Hartmann et al., 2002).
Our three objectives for this study were 1) to determine whether submist propagation systems could be modified for commercial-scale propagation, 2) to compare water usage between submist and traditional overhead mist propagation systems, and 3) to compare rooting of several shrubs and herbaceous perennials propagated in both submist and overhead mist systems. Two of five species in this study (sweetfern and blue star flower) are difficult to propagate using stem cuttings. The other three species, faassen nepeta (Nepeta ×faassenii ‘Six Hills Giant’), sweetgale (Myrica gale), and panicle hydrangea (Hydrangea paniculata ‘Grandiflora’) are easy to propagate.
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