Nutrition Management of Perennial Stock Plants to Optimize Cutting Quantity and Quality

Some popular garden perennials yield low numbers of viable cuttings per stock plant and/or produce cuttings that are slow to develop significant root mass, preventing propagators from meeting demand for rooted liners. Our objective was to determine the impacts of stock plant nutrition on number of potential cuttings, rooting percentage, and the subsequent root development of cuttings of some popular but difficult to propagate perennials. Gaura lindheimeri ‘Siskiyou Pink’, Dianthus ‘Pixie Star’, Perovskia atriplicifolia ‘Filigran’, and Salvia x sylvestris ‘May Night’, were evaluated using five treatments of 0, 50, 100,150, 200, and 250 mg·L‾¹ N. Greenhouse-grown stock plants were fertilized with a custom-formulated complete liquid feed for ten weeks at which time potential cuttings were counted, and the sample cuttings were taken for rooting.  Petiole sap nitrate was measured with a specific ion meter (Cardy) to correlate real-time nitrogen status to cutting yield and subsequent root growth. These measurements in turn were correlated with those obtained via capillary electrophoresis. For the taxa studied, overall performance of stock plants and cuttings including rooting percentage and root surface area and volume was optimized with the 100 and 150 mg∙L-1 N treatments.  Little benefit was obtained from the higher rates, but the 50 mg∙L-1 N treatment produced the lowest number of potential cuttings across all taxa.