The native grasses which were growing when Lyndon Johnson's grandparents came to this area in 1867 have largely disappeared through farming, overgrazing and other man-made causes. The original native grassland/savannah of this region included grasses such as Little Bluestem (Schizachyrium scoparium), Indiangrass (Sorghatrum avenaceum), and Big Bluestem (Andropogon gerardii).

"Improved" species of grasses were introduced over time to provide additional forage for grazing animals, and have replaces the native plants of the region. In many areas, common exotic species include Bermuda-grass (Cynodon dactylon), Oatgrass (Avena sativa), Rescue-grass (Bromus catharticus), Crabgrass (Digitaria ciliaris), King Ranch Bluestem (Bothriochloa ischaemum), and Johnson Grass (Sorghum halapense). The park is restoring a portion of the native mixed grass prairie in the Johnson Settlement to better interpret the 1860's time period when President Johnson's forebears established themselves in the area.