The effects of three different micro-catchment sizes on survival and growth of plant species was assessed and success in establishment and growth of Croton megalocarpus and Cassia spectabilis was compared in a semi-arid region of Kitui District, Kenya. Both species were planted in 25 x 25 cm, 45 x 45 cm, and 65 x 65 cm spherical micro-catchments. Height and diameter were measured and a survival count was taken. Results show that then micro-catchment size influenced (P>0.05) lateral growth of both species. Lateral growth of C. spectabilis in the smaller two micro-catchments (3.66 and 4.60 cm, resp.) was not significantly different (P>0.05), but was less than in the largest micro-catchment(5,31 cm). These results indicate that the two species are suitable for afforestation in these areas and that their survival is not limited by provision of a catchment in the area.