What Can I Plant on a Septic Mound?

Zone 3

• In USDA zone 3, average annual lows reach minus 40 degrees Fahrenheit. Day lilies (Hemerocalis spp.) are hardy in zones 3 to 10. These perennials bloom in a range of colors, from white to purple, and grow to 3 feet all. Oxeyes or false sunflowers (Heliopsis helianthoides) grow well on mounds. Hardy in zones 3 to 9, these 5-foot-tall perennials produce orange and yellow flowers with dark centers. They prefer full sun and well-drained soil. Pussytoes (Antennaria spp.) are hardy in zones 3 to 9 and spread into a mat of fuzzy, silvery, semi-evergreen foliage. They bloom with white and pink flowers. Pussytoes prefer sun to light shade and poor, sandy soil.

Zone 4

• In USDA zone 4, average lows reach minus 25 degrees. Fescue (Festuca glauca) thrives in zone 4. This ornamental grass grows in 10-inch-tall clumps of fine, blue-green foliage. It prefers well-drained or dry soil and full sun but tolerates light shade. Little bluestem (Schizachyrium scoparium) is hardy in zones 4 to 10. This upright grass grows to 4 feet tall and has green to blue foliage that turns bronze in fall. It prefers full sun and tolerates a range of soils.

Zone 5

• USDA zone 5's average low temperatures hit minus 15 degrees. Prairie smoke (Geum triflorium) are hardy in zones 5 to 9 and grow from 9 to 12 inches tall. These perennials bloom from late spring through early summer with pink flowers. They prefer well-drained soil and partly shaded exposures. Snapdragons (Antirrhinum majus) grow well on septic mounds. These annuals bloom from spring through fall in a range of colors and grow from 6 to 36 inches tall. They prefer sun to partial shade. Ornamental grass options for zone 5 include tumble grass (Eragrostrum spectablis), which grows to 2 feet tall and forms loose clumps of fine green foliage. It prefers sandy, poor soils, tolerates drought and is hardy in zones 5 to 8.

Zone 6

• To thrive in zone 6, septic mound plantings must tolerate average lows to minus 5 degrees. Carex (Carex spp.) is hardy in zones 6 to 8. This low-growing, ornamental grass prefers partial to full shade. It grows in clumps of variegated yellow, white and green foliage. Carex reaches heights of 6 to 18 inches. Sedum or stonecrop (Sedum spp.), a spreading groundcover, helps prevent erosion on mounds. This semi-evergreen forms a dense carpet of fine foliage. It is hardy in zones 6 to 8 and grows from 3 to 18 inches tall. Sedum prefers sun to partial shade and well-drained soil.