The present study reveals a variety of competitive interactions between the two species ofEuphorbia—Euphorbia hirta andEuphorbia thymifolia depending upon the calcium status of the soil. In general,Euphorbia thymifolia suffered high mortality in low calcium soils as compared toEuphorbia hirta. The former, however, showed better survival in high calcium soils. This was more pronounced in mixtures than in pure stands. A similar pattern of behaviour though not so pronounced was also recognised with respect to the growth performance of the two Species in low and high calcium soils. The significance of these results is discussed.