Determination of Optimum Fertilizer Concentration and Corresponding Substrate Electrical Conductivity for Ten Taxa of Herbaceous Perennials

Abstract

Little taxa-specific information is available regarding the nutrition needs of container-grown herbaceous perennials. The goal was to determine optimum fertilizer concentrations and corresponding substrate testing values for greenhouse production of 10 taxa. Astilbe chinensis (Maxim.) Franch. & Savat.`Purpurkerze', Campanula carpatica Jacq. `Deep Blue Clips', Coreopsis verticillata L.`Golden Gain', Gaura lindheimeri Engelm. & Gray, `Siskiyou Pink', Heucherasanguinea Engelm. `Mt St. Helens', Lamium maculatum L. `White Nancy', Penstemon ×hybridus Hort. `Sour Grapes', Perovskia atriplicifolia Benth. `Longin', Salvia nemerosa L. `Blue Hill', and Veronica × Hort. `Goodness Grows' were grown for 10 weeks with 15N–7P–14K at four rates (50, 150, 250, and 350 mg·L–1 N) of constant liquid feed. Substrate pH and soluble salts levels were measured weekly using the pour-through extraction method. In analysis of all taxa, most effects [quality, shoot dry weight, pH and electrical conductivity (EC)] varied by rate × taxa. Though higher levels of fertilizer produced the largest plants in some cases, satisfactory quality was also attained with a lower rate. Quality and pH were negatively correlated for a few genera but most showed no relationship. Results of this study indicate not all taxa tolerate increased fertilizer levels and that the herbaceous perennials studied could be grouped by nutritional needs. Furthermore, target ranges for EC can be developed based on dry mass and quality ratings.