Seagrasses are marine angiosperms and are considered ecosystem engineers [1]. However, despite their global ecological importance, seagrasses continue to decline worldwide [2]. In South Africa, Zostera capensis Setchell is endangered, and populations are fragmented and poorly protected [3]. Active restoration via transplantation has been attempted [4], but a sustainable source of donor material needs to be provided to limit pressure on wild populations. To refine the multiplication medium for the in vitro micropropagation of Z. capensis, a series of laboratory experiments were conducted to i) compare the elemental concentrations of the seawater and sediment from a site where Z. capensis naturally occurs to the artificial medium previously used in micropropagation and, ii) test the effects of providing different concentrations of sodium nitrate and monosodium phosphate as additional N and P supplies. The artificial medium had low concentrations of N and P (12.37 and 1.12 mg.L-1, respectively) whereas the sediment had much higher concentrations (300 ± 122.47 and 180.88 ± 15.98 mg.L-1, respectively). Experiments showed that the addition of either N or P up to the mean sediment concentrations led to significantly increased growth (mean relative growth index (RGI) values of 1.63 and 1.88, respectively), whereas their combination did not support increased growth (mean RGI value = 1.12). While further refinements of the multiplication medium are needed, this study has shown that matching nutrient concentrations to their natural environment supports increased growth of Z. capensis and contributes to the in vitro micropropagation protocol as a tool to support regional restoration.