Date of Potting and Fertilization Affects Plant Growth, Mineral Nutrient Content, and Substrate Electrical Conductivity

Abstract

The landscape industry uses containerized plant material throughout the year. Thus, traditional spring potting at many nurseries has changed to potting throughout the year. The objective of this study was to determine the effect of potting date and rate of fertilization on plant growth and mineral nutrient content, substrate electrical conductivity (EC) and pH, and winter injury. To complete this objective, rooted stem cuttings of Ilex crenata Thunb. ‘Compacta’ and Viburnum awabuki K. Koch. ‘Chindo’ were potted in Raleigh, NC, July 17, 1998; September 7, 1998; October 29, 1998; March 25, 1999; and May 13, 1999. Two controlled-release fertilizers [Wilbro/Polyon 15N–1.8P–7.5K (15N–4P 2 O 5 –9K 2 O) and Scotts 23N–1.8P–6.6K (23N–4P 2 O 5 –8K 2 O)] were applied at four rates: a split application with 0.5X incorporated at potting and surface application of the remaining 0.5X six months after potting date [X = manufacturers' recommended rate per 3.8 liter (4 qt) container], and 1X, 1.5X, and 2X incorporated at potting. Plant growth and mineral nutrient content were determined one year after initial potting date. Substrate EC and pH were measured monthly. ‘Compacta’ holly and ‘Chindo’ viburnum potted in September or October were larger than plants potted in March regardless of fertilizer and rates of fertilization. In general, holly and viburnum were smaller when fertilized with 0.5/0.5X compared to 1X regardless of fertilizer and date of potting. Within each rate of fertilization, viburnum potted in September had significantly greater N and P content compared to viburnum potted in March or May. Nitrogen and P content were highly correlated to plant dry weight ( r > 0.79, P = 0.0001). Mineral nutrient content of holly responded similarly. No plants were injured by winter temperatures regardless of potting date or rate of fertilization throughout the study period. Plants potted in July, September, or October had the highest substrate EC values in March, whereas plants potted in March or May had highest EC values in August regardless of species, fertilizer or rate of fertilization. Substrate pH was unaffected by date of potting, but pH decreased with increasing rates of fertilization.