Container-Grown Holly Response to Phosphorus

Controlled-release fertilizers (CRFs) often contain higher than 1.3 % P. Phosphorus applied in excess of plant demand is leached and likely transported in runoff from the nursery site.  One approach to achieving a reduction in P loss from the nursery is to reduce the amount of P applied. In our experiments, multiple-branched liners of Ilex cornuta ‘Burfordii Nana’, Ilex crenata ‘Helleri’, and Ilex vomitora ‘Nana’ were potted August 2006 with 10 L of a common nursery substrate. The substrate was amended with 4.2 and 0.9 kg/cubic meter of dolomitic limestone and Micromax^® micronutrients, respectively, and amended with 46 g of a CRF that differed in P content [18N-0P-10K, 18N-0.4P-10K, 18N-1.3P-10K, or 18N-2.6P-10K (Harrell’s Inc., Lakeland, Florida)]. Twenty plants were grown with each CRF under natural light and each container was irrigated with approximately 400 ml as needed. After 18 months, shoot and root dry weights of Ilex cornuta ‘Burfordii Nana’ were greatest for plants that received 18N-0.4P-10K and 18N-2.6P-10K, and Ilex crenata ‘Helleri’ responded similarly after 16 months. Shoot and root dry weights were not different after 17 months for Ilex vomitora ‘Nana’ that received P in the CRFs. Substrate pour-through P ranged from a high of 10 mg/L at week 8 for the substrate amended with 18N-1.3P-10K to 0 mg/L at week 24 for substrate amended with 18N-0.4P-10K. These results indicated that CRF with 0.4 % P was adequate for production of the holly species tested and its use in lieu of a CRF with a higher P content would be considered a best management practice.