A complete fractionation of P (i.e. total phosphorus, orthophosphate, dissolved phosphorus and insoluble phosphorus) in pore-water (i.e. solution residing in container substrate pores) of amended and non-amended soilless substrate has not yet been performed; furthermore, the determined fraction of total leachate P that’s in the form of orthophosphate has been inconsistent between studies (Million et al. 2007; Ristvey et al., 2004). Fractioning pore water P will provide insight on short-term quantity of plant available P in pore-water, as well as the immediate bioavailability of P leached from soilless media. We hypothesize that not all pore-water P is immediately plant available (orthophosphate). Thus, our results would allow us to make fertilization recommendations based on plant available P rather than total P in pore-water. Additionally, determining the proportion of dissolved and insoluble P in leachate would aid in our understanding of the container nursery’s environmental impact due to phosphorus runoff. Establishing a minimum P concentration in pore-water that will maintain maximal growth of woody ornamental plants has major implications for the nursery industry. Reducing fertilizer application rates and increasing uptake efficiency would reduce nursery production costs. Increasing uptake efficiency by minimizing necessary pore-water P concentration would increase crop phosphorus use efficiency, subsequently decreasing P leachate and runoff contributing to P loads in waterways. This will aid in improving water quality for aquatic ecosystems, and nurseries will be better able to meet state requirements for maximum nutrient runoff loads.