Effect of Irrigation, Fertilizer Rate and Placement, and Two Substrates on Growth of Rose and Hydrangea

Abstract

Current best management practices for containerized nursery crops maximize plant growth while minimizing nutrient leaching. This study tested how plant growth was affected by reducing the standard fertilizer rate when grown in two soilless substrates with different physical properties under two irrigation levels. Controlled-release fertilizer (CRF) treatments included 1.0x (45g) applied as topdress (TD), 1.0x (45 g) incorporated throughout (IT), or 0.75x (34 g) incorporated into only the top half (TH) of the container. Rosa ‘BAIneon' Screaming Neon Red™ rose and Hydrangea macrophylla ‘PIIHM-II' Endless Summer® Bloomstruck® hydrangea were potted using Aeration+Potting Mix (AS40) or All-purpose Potting Mix (PM2) substrates. Plants received higher [12.7 mm (0.5 in)] or lower [8.3 mm ( 0.33 in)] irrigation per day for 18 weeks. Final dry weight (DW) was most affected by fertilizer, to a lesser extent substrate, and not at all by irrigation. Regardless of taxa, the largest DWs were produced when plants were grown in PM2 and received nutrients via IT or TD compared to TH. Electrical conductivity was greatest in PM2 substrate with a 1.0x fertilizer rate, regardless if applied IT or TD. Taxa were unsaleable in the TH treatment, thus negating the environmental benefits achieved by reductions in leaching from lower fertilization rates. Species used in this study: ‘Screaming Neon Red™' rose (Rosa ‘BAIneon'); ‘Endless Summer® Bloomstruck®' hydrangea [Hydrangea macrophylla (Thunb.) Ser.]‘PIIHM-II').