In the traditional rubber-growing areas in the south-west region of Sri Lanka there is hardly any scope for further expansion of Hevea cultivation due to limited land resources. Moreover, the extent under rubber cultivation has shown a remarkable declining trend largely due to diversification of land for other alternative ventures. Expansion of rubber cultivation to areas marginal with regard to rainfall has become essential to increase the production levels. This paper, therefore examines possibilities and potentials of growing rubber under some marginal environmental conditions in Sri Lanka. The soil moisture distribution profile was studied along with the effect of soil moisture deficit on growth and latex production of Hevea. Based on these possibilities to overcome the adverse effects were suggested. Results obtained on the performance of recently developed RRIC 100 series clones when subjected to water deficit situations suggested that the clones RRIC 121 and RRIC 102 were superior to other clones tested such as RRIC 100, RRIC 110 and PB 86 even at the very low soil moisture level of 10;available water. It was further noted that the Leaf Water Potential (LWP) and Relative Water Content (RWC) were highest while Transpiration Rate (TR) was lowest in clone RRIC 102. Moreover, the clone RRIC 102 had the highest Leaf diffusive Resistance (LDR) compared to other clones confirming the ability of this clone in maintaining a higher water holding capacity under low soil moisture conditions. Effects of soil moisture on establishment success and early growth of rubber plants were studied by comparing the performance of five establishment practice under four levels of soil moisture. The growth of one whorled brown budded poly bag plants was found to be superior to other establishment practices such as one whorled poly bagged green buddings and young buddings, brown budded bare roots and green budded bare roots. In general, the plants raised in polythene bags appeared to have an initial advantage over the use of bare root budded stumps. Nevertheless as the root density of young buddings are higher, it is possible that the young buddings will eventually perform better under field conditions. Results obtained on the role of potassium and moisture on growth and water relations of Hevea brasiliensis showed that with watering at 50;depletion of available water level with recommended level of K, plant diameter was almost equal to the diameter with watering at 90;depletion of available water level in combination with double the recommended level of K. Plant physiological measurements made indicate a better plant water status in K sufficient rubber plants. Soil moisture storage capacity in plots that were mulched was much higher than in the other plots with natural or legumes. Moreover, some plant physiological measurements made indicate that the water status of plants was improved in plots that were in much comparison with the plants in naturals or legumes. It therefore appears possible to eliminate or at least minimize the adverse effects of moisture stress by mulching which also would enhance nutrient uptake by rubber, eventually improving growth as well as yield of rubber. Moreover, mulch with paddy straw was found to increase soil and leaf K content also. It is therefore suggested that rubber growing can be extended to areas marginal with regard to rainfall by choosing the appropriate clone such as RRIC 102, with the use of dead mulch preferably paddy straw, and higher levels of pottasium during the early stages of growth.