Comparison of Mist, Fog, and Electrostatic Fog for Vegetative Propagation of Difficult-to-Root Plants®
Richard Y. Evans, Wesley P. Hackett and Fernanda Larraín
There is an expanding market for nursery-produced native California plants, but their production is limited because many are difficult to propagate from cuttings. We are studying two barriers to successful propagation: low competence of stem cuttings from source plants and deterioration of cuttings due to environmental conditions during rooting. The primary objectives of the project are to test methods for improving the competence of difficult-to-root species by the manipulation of stock plants, and to test novel fog chambers to enhance the rooting environment. We used three types of bottom-heated propagation benches: standard mist benches and fan-and-pad-cooled fog chambers with either standard or electrostatic fog nozzles. Leafy cuttings of Carpenteria californica, Dendromecon rigida, Garrya elliptica ‘Evie’ and G. elliptica ‘James Roof’, Rhamnus californica ‘Eve Case’, Ribes speciosum, and Romneya coulteri were taken from containergrown stock plants maintained in either a greenhouse or a lath house or from plants in the University of California Davis Arboretum. We found no consistent effect of either propagation bench type or concentration of IBA on rooting percentage. Higher rooting percentages were obtained from greenhouse-grown plants and plants growing outdoors yielded the lowest rooting percentages. The highest rooting percentages for most species (from 48% for G. elliptica ‘Evie’ to 80% for C. californica) were obtained from cuttings taken in January from plants grown under HID lamps in a greenhouse. However, it is not clear whether the lower rooting percentages in other seasons were due to cutting source material or inadequate environmental control in the propagation chambers. Rooting percentages for Rhamnus cuttings were consistently high, averaging 81% across all experimental conditions. Average rooting percentages in fog chambers over time for the other species were 44% for Carpenteria, 5% for Dendromecon, 38% for G. elliptica ‘Evie’, 32% for G. elliptica ‘James Roof’, and 23% for Romneya. Propagation of Ribes in the fog chambers was unsuccessful.
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