I’d like to plant a shrub or small tree at the corner of my house where the septic line runs to the leach field, but I’ve heard that certain plants seek water sources and invade the pipes of septic lines. What tree or shrub choices do I have for that location, if any?
Cynthia Reiser, Shannock, RI
Scott Clark, an extensioin agent at the Cornell Cooperative Extension Service in Riverhead, New York, replies: Your concern is shared by many, but there is no real cause for alarm. Tree roots do not search out water sources like the tentacles of an octopus in search of prey. Most small tree roots stay in the upper 12 to 15 inches of the soil where adequate water, oxygen, and nutrients are available. The more expansive roots from larger trees, such as Norway maples, poplars, or willows, that were found in old, broken sewer lines made of clay in days past may have given rise to this myth. The easily-cracked sewer lines were the problems, not the trees. Today, sewer lines are made of sturdier materials such as PVC pipe which are much less prone to cracking.
You should be more concerned about selecting a pest-resistant shrub or small tree that complements your site. Crabapples (Malus spp.) offer spring flowers and come in a variety of smaller sizes. Be sure to choose a disease-resistant cultivar. Kousa dogwood (Cornus kousa) grows to 20 feet with white flowers in early summer. Its reddish-purple fall color and red fruit are also appealing. Doublefile viburnum (Viburnum plicatum var. tomentosum) is a worthy shrub that reaches 10 feet with double rows of showy white flowers in spring. Its red fruit changes to black in late summer, and the reddish-purple fall foliage is attractive. Seibold viburnum (Viburnum seiboldii) is a seldom used viburnum which grows to 15 feet, has creamy white flowers in late May, and red to black berries which attract birds. These plants are hardy to Zone 5.