By Shannon Grina, Certified Professional Horticulturist, Grina Landscape Design, LLC
Not all of us have clients lucky enough to be connected to public sewer systems. Many properties in unincorporated or rural areas have septic systems otherwise known as “on-site sewage systems”. Living here in Gig Harbor I find that about 50% of my client properties require designs that can accommodate septic tanks and drain fields. Often the most challenging aspect of this is that clients rarely know where their septic equipment is located and have grand plans for decks, sheds, orchards and trees in areas that would negatively impact their septic systems.
Realities of Septic/Onsite Sewage Systems
Residential septic systems are designed as “private sewage treatment plants”. A drain field disperses sewage fluids into the soil for treatment by soil organisms and minerals prior to reaching the site’s groundwater. Systems are designed specifically to provide the optimal conditions for this to work properly. Interfering with the drain field by compacting or adding soil, adding excess water, or adding plants with extensive root systems will only create future problems by inhibiting the soil from doing its job in cleaning the sewage. Additionally, septic tanks need to be pumped every 3-5 years, therefore access is essential. Even in optimal conditions septic systems may fail over time due to homeowner misuse or lack of maintenance. Anything installed over a septic tank, drain field or reserve drain field runs the risk of future removal.
Locating a septic system
The first step is to locate a “record drawing” or “as-built” design of the septic system in relation to the house and property boundaries. These are documents generally required to be part of the home’s documents provided at the time of sale and may also be requested from Public Health Departments of the county in which the home is located. Beware that these records are not always accurate and older homes may not have record drawings at all. One of my clients was provided a design from the county that is completely illegible. Should no drawings be available, I require clients to hire a septic maintenance company to come out and determine the exact location of septic tanks, existing drain field lines and reserve drain field areas.
All Photos: Grina Landscape Design, LLC
After obtaining the septic system drawing, the tank, drain field and reserve area should be located and marked out utilizing the drawing and at times, exploring the site. Most septic maintenance companies can aid in doing this.
It is a good idea to plan to install risers on septic tank lids for ease in septic pumping and to avoid future landscape problems. I recommend installing these at ground level as that allows for more options to conceal the lids in a design. These lids can be successfully camouflaged with billowing perennials or grasses, containers or birdbaths.
Area where a hidden septic tank lid was covered with soil
Highly visible septic tank lids
Septic tank lids set at ground level
Once everything is sited the design work can begin.
Be aware that any construction work done on or near the septic tank or drain field runs the risk of damaging tanks and pipes and compacting soil. A client of mine had their drain field lines smashed when a contractor ran heavy equipment over the drain field lines while installing a boulder retaining wall. The contractor was liable for all damage. Make certain that all contractors doing installation work are aware of all the septic systems components’ locations.
Reserve drain fields are designed to be used should the main drain field fail or if the house is renovated in a way that requires additional or updated septic accommodations. Therefore the reserve area must be left available for potential future use. In the photo below the previous owner had built a shed on the reserve drain field. We removed this and built another shed completely outside the septic area.
Shed installed over reserve drain field area
Woody trees should never be planted in drain field areas, especially water-loving trees and shrubs. It is recommended that all woody trees and shrubs be planted at least 20’ away from drain field lines and tanks. In the photo below, the client had planted over 20 trees including a weeping willow on their drain field. All trees had to be relocated to new locations outside the drain field area.
Numerous trees planted directly on a drain field
Willow tree relocated to a minimum of 20 feet outside the drain field
Here is a summary of guidelines for landscaping for septic/on-site sewage systems:
- No vegetable gardens may be built on or near the drain field or reserve area
- Do not reshape or fill the ground surface over a drain field or reserve area. Topsoil can be added only as long as it doesn’t exceed a couple of inches as it will limit air exchange that is critical for proper functioning
- Use only shallow-rooted, low-water plants. Low-maintenance perennials and shallow-rooted grasses are best
- Avoid all water-loving plants and trees as well as woody shrubs
- All surface drainage should be directed away from septic systems
- Grass/existing native vegetation are generally the preferred covers for drain fields and reserve areas (products like meadow mixes, Eco-turf, Fleur de Lawn often work well as they utilize native grasses and shallow rooted flowers)
- Do not put plastic sheets, landscape fabric, bark, gravel, sprinkler lines or other fill over the drain field and reserve area
- Note that plants over the septic system may be disturbed or destroyed with future septic maintenance or repair work
- Do not locate ponds on or near the septic system
These before and after photos show how original junipers were removed and the landscape redesigned using shallow-rooted and low-water perennials to accommodate the existing septic system.
Overgrown, woody shrubs were located near the home’s drain field and their roots were impacting the drain lines.
Water was redirected from downspouts and lawn runoff into the new dry creek bed. Shallow-rooted, low-water perennials were installed as well as new lawn over the drain field area. Functional for a septic system and still beautiful in summer.
Summer color abounds on this slope with low-water, low-maintenance shrubs and perennials
Still beautiful in winter
Before even starting a landscape design for a property with an on-site sewage system, require an as-built drawing and verify locations of all septic system components. Then manage client expectations of exactly what is allowable in these areas. Design with appropriate plant materials that are generally shallow-rooted, low-water perennials and grasses. Direct excess water away from drain fields and reserve areas. Finally, insist installation contractors use caution and avoid running any heavy equipment over the drain field areas. Done properly, a beautiful result is completely obtainable.
There is much information available online. I found these two sources to be the most helpful for any landscape design involving septic systems or on-site sewage systems:
King County Public Health site and Clark County WSU Extension site