A significant amount of genetic diversity exists within Kentucky bluegrass (Poa pratensis L.) for many characteristics including growth habit and stress tolerance. The identification of Kentucky bluegrass cultivars with improved rooting capability under heat stress would benefit sod growers and turf managers attempting to establish and maintain sod during the summer months. The objective of this study was to determine the genetic variation in rooting characteristics of Kentucky bluegrass cultivars and selections during heat stress. Twenty-seven Kentucky bluegrass cultivars and selections including two Texas x Kentucky bluegrass (P. arachnifera x pratensis) hybrids were chosen to represent the Kentucky bluegrass classification types. Sod plugs (10 x 30 cm) were removed from a turf trial established in 2003 at the Rutgers University Department of Plant Biology and Pathology Research Farm in Adelphia, NJ, in the summers of 2006 and 2007. Soil and roots were cut to 3.75 cm below the thatch from all sod plugs. Plugs were planted in four liter pots and filled with a 3:1 sand:soil mixture filled to a height of 36 centimeters (and standard weight of 4.2 kg). The potted sod plugs were then grown at the Rutgers University Plant Biology and Pathology Research Farm in North Brunswick, NJ, in a completely random design with three replications in an area with restricted air movement that maximized heat stress. Drought stress was avoided by watering to soil capacity daily during the study. Three replicate pots of each cultivar or selection were harvested at two, four, and six week intervals. The soil profile was separated into seven cm increments (1-7, 7-14, 14-21, 21-28, and 28-35 cm). Roots were washed free of the sand:soil mixture, stored in a ten percent methanol solution at 4°C and then put through a soil sieve (0.8 mm mesh) to remove any fine particles. Roots were dried at 55°C for 48 hrs. The study was repeated twice at five week intervals throughout July and August to maximize the occurrence of natural heat stress events. Differences in rooting ability under heat stress were observed in Kentucky bluegrass. Some cultivars and selections, including Cabernet and Eagleton (typical Mid-Atlantic types), grew fewer roots quickly into the deep profiles and then begin to branch. Compact-Midnight type cultivars grew roots more slowly, but had a higher amount of roots that gradually colonized the sand:soil media. Other cultivars such as Baron did not produce roots deep in the soil profile even at the end of the six week study period. The dramatic differences observed in rooting characteristics under heat stress indicate that Kentucky bluegrass cultivars and selections are adapted for different niche uses. These rooting characteristics can help turf managers select cultivars with deeper and faster rooting capability during summer stress which could improve the success of establishing sod during the summer months. Additionally, specific cultivars can be chosen that maximize soil stabilization or filter runoff water.