Zinc oxide is a very promising material for short-wavelength light-emitting devices due to its large band gap and high exciton binding energy. Although great progress has been made in recent years, p-type doping and control over native defects introduced during or after material growth are still significant problems that hinder the development of efficient ZnO based optoelectronic devices. Here we demonstrate a versatile method for the growth or p-type or n-type ZnO nanorods from the same growth solution at temperature as low as 90 degrees C, where the conductivity type is controlled by the preparation of the seed layer for nanorod growth. The differences in the conductivity type can be attributed to dependency of native defect concentrations and hydrogen incorporation on the seed layer preparation method. Room temperature electroluminescence has been demonstrated from homojunction and heterojunction light emitting diodes containing p-ZnO nanorods.