The middle and lower slopes of Hager Mountain are covered in a pine forest with an understory dominated by low sagebrush. Other understory shrubs include curl-leaf mountain mahogany, and antelope bitterbrush. Low groundcover plants include Indian paintbrush, yellow balsamroots, nineleaf biscuitroot, scabland fleabane, woolly sunflower, common yarrow, low pussytoes, and slender phlox. Common grasses on the mountain include Idaho fescue, bluebunch wheatgrass, wild rye, prairie junegrass. A few western junipers grow on the lower slopes on the northeast side of the mountain.