Controlled-release fertilizer type and rate affect landscape establishment of seven herbaceous perennials

Abstract

Use of controlled-release fertilizers (CRF) has been recommended to the landscape service industry as a best management practice for establishing landscape plants. However, application practices vary considerably among professionals and recommendations are lacking for the appropriate type (tablet vs. granular), application rate, and timing of CRF to establish herbaceous perennials. In this study, cigar plant (Cuphea ignea), daylily (Hemerocallis 'Stella de Oro'), gaura (Gaura lindheimeri 'Siskiyou Pink'), lantana (Lantana camara 'New Gold'), mexican heather (Cuphea hyssopifolia), purple coneflower (Echinacea purpurea), and rudbeckia (Rudbeckia fulgida 'Goldsturm') were fertilized with granular CRF (GF) 15N-3.9P-10K (8 to 9 month) at 0, 1, 2, or 4 lb/1000 ft2 nitrogen (N) at transplant (no fertilization, GF1, GF2, and GF4, respectively), a split application of GF with 1 lb/1000 ft2 N applied at transplant and 1 lb/1000 ft2 N applied 5-months later (GF2-split), or tablet CRF 16N-3.5P-10K (8 to 9 months) at two tablets per plant (7.5 g) at transplant (TF2). Plant size and visual quality (VQ) at 5 months after transplant (MAT) were improved by fertilization for all perennials except 'Stella de Oro' daylily. Compared to GF2, GF4 improved the growth of perennials of larger size and greater biomass production (i.e., cigar plant), but did not further improve their VQ. All perennials grown with TF2 had similar size and quality as those grown with GF2 at 5 MAT. At 15 MAT, no difference was found among fertilizer treatments for surviving perennials except cigar plant. Split application (GF2-split) did not improve overwinter survival or second-year plant growth and quality for most species when compared with GF2. On the basis of these results, we recommend applying two tablets (7.5 g) of 16N-3.5P-10K per plant at transplant to establish the perennials tested in this study.