Only natively-occurring plants of this taxon have been observed. Little is known of the San Clemente Island indian paintbrush's reproductive phenology. Anthesis occurs from February through April and fruiting from April through June. Nothing is known concerning pollinators or seed dispersal of this plant. The greenish-yellow color of the flowers and bracts, however, would counterindicate hummingbird pollination which is otherwise frequent in the genus.
Nothing is known to be reported about the population biology of the plant.
Although no field examination of root-haustoria connections have been done or are known to be reported, Castilleja grisea occurs frequently in association with Opuntia littoralis and to a lesser degree, with Isocoma veneta. The plant is presumed parasitic by its being within the genus Castilleja. In canyon areas it is a very infrequent plant. Also, grazing by feral goats and pigs has destroyed accessible shrublands when not precluded by barrier cactus patches. U.S. Fish and Wildlife Service. 1984.