The potential uses of hydrophilic nanostructured microporous polymers (PolyHIPE polymers) in agriculture were investigated with rye grass as a model plant. The basic material was crosslinked styrene-divinyl benzene polymer with a 90 vol % porosity. They were microwave-sulfonated to obtain hydrophilic polymers with water adsorption capacities of 10-fold and 18-fold with nominal pore sizes of 20 and 150 mu m, respectively. The small-pore-size PolyHIPE polymer was rigid, whereas the large-pore-size polymer was spongy and adsorbed water rapidly. When this spongy polymer was used as a soil additive at 0.5 wt % with increasing water stress (normal, semiarid, and arid conditions), the dry biomass yield increased by about 30, 140, and 300%, respectively, after 21 days of cultivation compared with the control, which contained no sulfonated spongy PolyHIPE polymer. The rigid sulfonated PolyHIPE polymer did not show any statistically significant effect on the biomass yield. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 3292-3299, 2010