Landscaping over a septic system is a challenge for many homeowners. Anything planted near a septic system needs to have shallow roots so that the drain tiles aren't clogged. Virginia Cooperative Extension recommends few trees for planting near septic systems, and suggests planting them between the drain lines or at the end of the drain field. Loosening and amending the soil well before planting, and preparing an area as wide as the expected root zone of the tree will encourage the roots to stay within that area.
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Flowering dogwoods (Cornus florida) thrive in moist, organic soil a bit on the acid side, so North Carolina State University recommends mixing peat moss or leaf mold into the soil when preparing the planting site. Dogwoods grow 20 to 30 feet high. In addition to the large spring flowers, dogwoods have brilliant red foliage in the fall. Mulch well around the base of the tree, not only to conserve water but to protect the trunk from injury by lawn mowers or weed-eaters. The cultivar Cherokee Chief has reddish-pink flowers instead of white.
Crabapples (Malus) are small to medium trees grown for their exuberant display of spring flowers and ornamental summer fruit. Flowers are single, semi-double or fully double, and are white, pink or red. Plant crabapples in full sun, and prune away any suckers growing up from the roots. The newer dwarf varieties are good choices for planting near septic lines, because they have small root systems. Colorado State University Extension recommends Lancelot, a 10-foot tree with red and white flowers and yellow-gold leaves in fall, or Sargent Tina, a 5-foot dwarf crabapple with white flowers and fruit that attracts birds into the garden.
There are many varieties of ornamental cherry trees (Prunus) available, but as always when planting near a septic system, choose one of the smaller types. Clemson University Cooperative Extension recommends Shogetsu, also sold as Shimidsu, which grows 15 feet tall, but is much wider. It has pale pink, double flowers in late spring. The purple-leaf sand cherry (Prunus x cistena) is a delicate, 7 to 10 foot tall tree with single, pink flowers in spring. Plant ornamental cherries in full sun, and mulch around the base to protect the trees from mechanical injury.