Effects of varying shade and fertilizer on the growth ofZamia floridana A. DC

Abstract

It has repeatedly been noted that ready availability of well-grown cycad specimens would substantially reduce collection of plants from their natural habitats. Although some cycads are extensively produced in several countries, there is uncertainty as to their optimal growing conditions and fertilizer requirements. UsingZamia floridana (sensu lato) as a model, one-year-old seedlings were grown in 30% and 50% light-exclusion shadehouses for one growing season. They were fertilized with roughly equivalent nutrient proportions of 20-20-20 (N-P-K) Peters solution at 300 ppm applied biweekly, nine-month 18-6-12 controlled-release Osmocote granules, and 16-8-12 Controlled Release Sierra Tablets plus minors at two and three tablets per container, and in combinations. There was interaction between shade and fertilizer types in all parameters measured. Overall, plants grown in 30% shade had a larger caudex, more leaves, and higher leaf and stem-plus-root fresh and dry weights. Peters fertilizer at 300 ppm was least effective in all growth parameters, as compared with other fertilizer treatments. Alone, however, it was more effective in caudex enlargement in 50% shade. No differences were observed between any treatments involving granules, irrespective of supplemental Peters. There was no significant difference between three tablets plus Peters and two tablets only, in 30% and 50% shade. Two tablets plus Peters and three tablets only, however, had a significant effect on caudex enlargement in 30% shade. In 50% shade, three tablets plus Peters or granules alone were more effective. These results and personal experience show that nearly all cycads grow best in ± 30% shade and benefit from fertilizers that contain micronutrients and a higher ammoniacal nitrogen source.