The two main reasons for putting plants on effluent fields (ETS Field) are:
- To soak up the wastewater and transpire (the plants version of perspiring) it out through the plants foliage.
- To absorb nutrients out of the wastewater so that it does not make its way into the underground water table and so on into stream systems.
Thus, plants that have a high transpiration rate, vigorous growth and are tolerant of wet soil conditions are best. Plant spacings will vary depending upon species and mature size, but it’s generally calculated at 1 plant per square metre of field. Thus a 200m square field should have 200 plants and so-on. When planting smaller grasses or lilies you may space them at 50-75cm while medium sized trees may be spaced at 1.2-1.5m, so overall with a mixed species planting it is typically 1 plant per metre.
The key differences between the two common types of effluent fields are:
- Underground pipes (usually 100mm diameter pipes with small seepage holes along its length and buried 600mm underground)
- Dripper lines on the ground surface (usually 15mm diameter hoses with drippers laid under mulch).
The biggest concern for the fields with underground pipes is the possibility of damage from large tree roots or blockage of the seepage holes along the pipes. Blockage is most likely to happen with deep rooting trees, or trees that will put out masses of feeder roots into water. Many of the plants listed below can be viewed on our website. www.alter-natives.co.nz Or by visiting our nursery: Alter-Natives Nursery & Landscaping, 101 Kioreroa Road, Port Whangarei, Whangarei 0110
Sources of information:
Auckland Regional Council Technical Sheet G-1: List of water tolerant plants suitable for on-site wastewater disposal systems.
Northland Regional Council: Looking after your household sewage system.
Above documents have been used by most engineers around Whangarei and Northland.