Overhead mist revolutionized the propagation industry by providing reliable means to manage transpirational water losses 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, OM has potential drawbacks, including the use of large volumes of water, potentially unsanitary conditions created by persistent water films on leaves (Preece, 2003), the potential for anaerobic conditions in the rooting zone, the depression of root-zone temperatures by evaporative cooling (Hartmann et al., 2011), nonuniform misting coverage, leaching of foliar nutrients (Preece, 2003), difficulty controlling cutting nutrition during propagation (Hartmann et al., 2011; Zhang and Graves, 1995), and the need to extensively acclimate cuttings to a low-humidity, mist-free environment.
Several authors have considered alternatives to OM for propagation of plants by stem cuttings, which we refer to here as SI, SM, and SF (Zhang and Graves, 1995). Graves and Zhang (1996) evaluated the suitability of SI for the propagation of several woody and herbaceous plant species, and found that such a system can be an effective alternative to OM. Moreover, Zhang and Graves (1995) found rooting could be improved in SI when a fertilizer solution was used instead of water. Another alternative system that merits investigation relies on the application of mist from below the cutting, to the base of the stem inserted into an enclosed chamber. Several such aeroponic systems are available on the market for use by home gardeners, but do not seem to be marketed for commercial propagation. Several authors have evaluated SM aeroponic systems for propagation of plants by stem cuttings, with promising results (Mehandru et al., 2014). Another aeroponic product on the market (Cyclone Ultrasonic Fogger; FutureGarden, Lindenhurst, NY) can be used to supply a fog of nebulized water or fertilizer solution to the bases of cuttings inserted into a rooting chamber. To our knowledge, the potential efficacy of this system for propagation has not been formally evaluated in the academic literature.
We speculated that each of these systems might offer several of the following advantages to OM for the propagation of plants by leafy stem cuttings. These include limited water usage, increased sanitation and reduced foliar disease pressures, superior oxygenation to the rooting zone, maintenance of high root-zone temperatures in the absence of evaporative cooling, uniform application of water to each cutting, no leaching of nutrients, efficient delivery of water-soluble fertilizer during propagation, and a reduction in acclimation requirements typical of cuttings accustomed to receiving foliar mist. Moreover, in two of the systems (SM and SF), root development could be assessed in situ without disturbing fragile, developing roots. Our aim here was to conduct a proof-of-concept evaluation to explore the general merits of each system.
The primary objective of this study was to compare rooting and posttransplant performance of coleus propagated in four propagation systems: traditional OM, SM aeroponic, SF aeroponic, and a modified SI system. The second objective was to determine whether the addition of water-soluble fertilizer was beneficial in any of these systems.
Crawford, B.D., Dole, J.M. & Bergman, B.A. 2016 Influences of season and cutting week within a propagation cycle on rooting of ‘Stained Glass’ coleus shoot tip cuttings are not overcome by rooting compound treatment HortTechnology 26 620 627
Currey, C. & Lopez, R. 2014 Controlled-release fertilizer during cutting propagation affects growth and tissue nutrient concentrations of rooted cuttings of annual bedding plants HortScience 49 152 159
Graves, W.R. & Zhang, H. 1996 Relative water content and rooting of subirrigated stem cuttings in four environments without mist HortScience 31 866 868
Hartmann, H.T., Kester, D.E., Davies, F.T. & Geneve, R.L. 2011 Hartmann and Kester’s plant propagation: Principles and practices. 8th ed. Prentice Hall, Upper Saddle River, NJ
Hoagland, D.R. & Arnon, D.I. 1950 The water-culture method for growing plants without soil. California Agr. Expt. Sta. Circ. 327 (revised)
Maroya, N., Balogun, M., Asiedu, R., Aighewi, B., Lava Kuma, P. & Augusto, J. 2014 Yam propagation using ‘aeroponics’ technology Annu. Res. Rev. Biol. 4 3894 3903
Mehandru, P., Shekhawat, N.S., Rai, M.K., Kataria, V. & Gehlot, H.S. 2014 Evaluation of aeroponics for clonal propagation of Caralluma edulis, Leptadenia reticulata, and Tylophora indica – Three threatened medicinal Asclepiads Physiol. Mol. Biol. Plants 20 365 373
Santos, K.M., Fisher, P.R. & Argo, W.R. 2009 Stem versus foliar uptake during propagation of Petunia ×hybrida vegetative cuttings HortScience 44 1974 1977
U.S. Department of Agriculture 2016 2014 census of horticultural specialties. 27 May 2016. <https://www.agcensus.usda.gov/Publications/2012/Online_Resources/Census_of_Horticulture_Specialties/>
Zhang, H. & Graves, W.R. 1995 Subirrigation to root stem cuttings: Comparison to intermittent mist and influence of fertilization HortTechnology 5 265 268