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Moisture is the major factor determining the success of the seedling establishment in arid lands. Thus, our goal were to investigate the effect of amount and frequency of watering events on two successional (late and mid-seral) grasses species of the western U.S. The study was conducted in greenhouse condition simulating the warm season temperature and humidity (May-August) in the South Plains of Texas. We simulated three summer monthly precipitation regimes (May�August) based on Long-term Precipitation Average (LPA) of Lubbock-Texas. The precipitation regimes treatments were: 1o) LPA, 2o) Dry regime (75% below of the LPA), and 3o) Wet regime (Average of ten-years with highest precipitation in the LPA). Also, we used the monthly precipitation to simulate three watering patterns: 1) monthly precipitation distributed in six events 2) monthly precipitation distributed in four events, and 3) monthly precipitation distributed in two events. Blue grama (Bouteloua gracilis) and Kleingrass (Panicum coloratum) were grown in 90 pots each contend 19 kg of soil. The germination and survival rate were measured weekly. 120 days after planting the plants were washed from the pots with cold water and measured the following variables: Biomass total (g of dry-matter), shoot and root length (mm). The data was subjected to analysis of variance and means were compared by Tukey test (P<0.05). ��The plants showed high mortality in dry years when the monthly precipitation was divided in six times There was correlation between water available and root biomass in Blue grama, but there was not in Kleingrass. �We believe strongly that this result is related with genetic factors associated with adaptations to water-limited conditions. Our results suggest the existence of an optimum range between frequency and amount of water inputted to the system of each plant species. This optimum range allows the seedling survival, establishment success, and initial development.