Flourensia cernua grows in desert scrub and desert grassland. It has increased in abundance in these habitats during recent times as a result of overgrazing, which reduced the native grasses, particularly grama grasses and tobosa. It is an indicator of Chihuahuan Desert scrub, which covers about 70% of the Chihuahuan Desert. There it codominates with creosotebush and viscid acacia. Other common plants associated with tarbush include whitethorn acacia, catclaw acacia, honey mesquite, Berlandier wolfberry, mariola, Wright's beebrush, littleleaf sumac, broom snakeweed, winterfat, and smooth-leaf sotol. It is part of many plant communities and is dominant in many types of desert habitats and ecotones. It is often the main shrub in a landscape otherwise populated by grasses. It may be sparse or locally abundant, growing scattered about the terrain or in dense stands. It may form monotypic stands in soils of clay and silt, such as those on bottomlands. It is most common on alluvial soils derived from limestone, the main parent material for the soils of the Chihuahuan Desert. The species has been described as long-lived.
