Grey water is wastewater from a household that does not contain human or animal waste. If properly collected and filtered, it can be used to water ornamental plants or plants that are not used as a food source. Grey water is alkaline due to the detergent content, so plants that live in alkaline soil with large root systems are the best plants to absorb grey water. The Ph of greywater can range from 6.5-8.7.
Eastern red cedar
The eastern red cedar (Juniperus virginiana) is an evergreen with aromatic wood and a pyramidal growth habit that grows to 90 feet in the right conditions. The eastern red cedar can consume up to 90 gallons of water per day and is tolerant of alkaline soil with a Ph level up to 8.0.
The Japanese barberry (Berberis thunbergii) is a thorny shrub that grows to 6 feet tall. It can form a thicket and in some states is considered invasive. However, it is tolerant of alkaline soils, up to a Ph of 7.5, that occur around grey water disposal sites.
The common lilac (Syringa vulgaris) can tolerate a Ph of 7.8, which is fairly high for a blooming plant. The common lilac shrub is very attractive with fragrant purple blossoms in the spring or summer and attractive leaves. It is long-lived and grows 20 feet tall and 20 feet wide. It is also adaptable to wide range of soil textures from sand to clay.
The eastern redbud (Cercis canadensis) tolerates a wide range of soil conditions but will thrive in a higher Ph range than most plants. It can live in limestone outcroppings with a Ph of 7.5 or higher. It has pink or magenta blooms in early spring followed by heart-shaped leaves. The eastern redbud is an attractive choice for the grey water disposal area.
For a large tree that is tolerant of the alkaline conditions present in a grey water drainage field, consider the bur oak ( Quercus macrocarpa.) It is a thick growing oak with a large, open crown. The bur oak can get very large and live 100 years or more. The soil, however, around the grey water drain field should be loose and well drained for a bur oak to survive. The root system of a bur oak is very large and can descend into the ground 15 feet or more. It grows well in soil with a Ph up to 7.5.