Xanthorrhoea johnsonii is predominantly an outcrossing species according to Borsboom (2005). This means that X. johnsonii cross polinates with other species to create variants of itself, creating a mixed mating system.
When populations of grasstrees are small the likelihood of self-polination is higher. The general number to look for in breeding species is about 500 in order to avoid long-term loss of genetic variation.
