Kenaf core fiber (KCF) could become a good growing substrate as the material is renewable, easy to handle, lightweight and low cost. However, KCF has poor chemical and physical properties due to its low cation exchange capacity (CEC) and water retention capacity. The research was conducted to determine the effects of different concentrations of zeolite incorporated to KCF substrate media on growth and development of some selected annual flowers; to examine and improve the physical and chemical properties of the substrate consisting of KCF by applying different rates of slow- release fertilizer; determine the effects of different rates of slow-release fertilizer on growth and flowering of marigold plants grown on KCF containing different concentrations of zeolite; and finally to determine the effects of KCF containing zeolite on growth and flowering of marigold, celosia, and cosmos plants.