Poly (butylene succinate) (PBS) and PBS-based polymer are important and promising replacements for petroleum-based and nondegradable polymer due to their biodegradability and good mechanical properties. In particular, agricultural products (such as mulch film and controlled release fertilizer) are attractive applications because plastics could be left in the field to decompose along with other organics. Poly (hexamethylene succinate) (PHS) is a novel bio-based and biodegradable polyester with similar chemical structure and good compatibility with PBS. This work details the production of PBS, PHS and P(BS-co-HS) random copolymer using two-stage melt polymerization via esterification and polycondensation. The thermal properties, mechanical properties, degradability and diffusivity of PBS were proved to be tunable via copolymerization with PHS. These copolyesters with tunable degradability and diffusion provide a flexible platform for design of a controlled-release fertilizer. By adjusting chemical structure, both diffusion and degradation rate can be controlled to achieve bimodal nutrients release. In this work, the diffusion coefficient (D) of phosphate ions through the copolyesters was determined based on Fick’s first law of diffusion in one dimension. The early nutrient release modality is determined by D and the second modality can be tuned through degradation of the polymer. This work will also discuss the effects of coating application technique on controlled release.