Black walnut pollen was germinated on liquid and agar-based media containing 20% sucrose, a requirement for germination and normal tube development. Boron (100 ppm boric acid) added to this medium slightly enhanced germination. Germination occurred only in dense (150+ grains/mm2) populations of pollen on the agar medium. This population effect was not overcome by the addition of Ca2+ to the medium, but germination in the sparse areas (< 30 grains/mm2) was occasionally promoted by high boron concentrations (600 ppm boric acid). Wide tree-to-tree variation in percentage of germination was observed.Vacuum-drying periods, ranging from 5 to 30 min, resulted in a gradual reduction of viability. Pollen was stored at −30C and −196C for 3 months without major loss of viability.