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Guide to Planting Over Septic System Components - photo illustrated SepticAPedia © Enter your search terms Submit search form   Search This Website - InspectAPedia.com

• Advice for planting over or near septic systems
• Grasses, flowers, ground cover near septic systems
• Trees or shrubs planting near septic systems
• Gardening over or near septic system components
• Ground cover over septic fields
• Using root killers or roto-rooters for septic systems

Planting Guidelines for Septic Drainfields, Mounds, Raised Beds, Septic Tanks and other Septic Components

This chapter discusses the types of plants that should or should not be planted over or near septic fields or other septic system components. Planting trees, shrubs, and even some ground covers over septic system components are causes of septic system failure in the drain field, leach field, seepage bed, or similar components.

This is a guide for homeowners who are planting trees, shrubs, gardens, ground cover, or other plants near a septic system and who need to know that can be planted near or over septic system components like the septic tank, distribution box, and drain field or soil absorption system. Planting the wrong things or in the wrong places can lead to the need for expensive septic system repairs. © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use the links at page left to navigate this document or to go to Other Website Topics. Green links at left show where you are in our document & website.

Planting grasses or flowers over septic fields

Many people have written to ask what can be planted over a septic field. Grasses, weeds, flower are OK: The best answer is grass or native grasses and weeds. Flowers are ok so long as they are not varieties which send down deep roots. In the photograph above these relatively shallow-rooted flowers were set around a septic tank cleanout cover. They won't cause any damage to the system. But when planning your planting arrangement for flowers over a septic tank, remember that if you plant valuable flowers too close to the access cover to a septic tank or distribution box, those plants may be damaged or destroyed when you have to excavate to open the tank or D-box cover. Basically, any shallow-rooting planting will be fine to plant over the surface of or near septic tanks, distribution boxes, or septic drainfields.

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  PLANTS OVER SEPTICS
     Gardens Near Septics
     Grasses or Flowers
     Grazing, Animals
     Ground Cover, Ivy
     Trees or Shrubs
     Using Root Killers
     Using a Roto Rooter

Grazing Animals Over Septic System Fields?

Is it acceptable to permit grazing animals such as cows, horses, or sheep to occupy a field over a septic system? No, placing horses, cows, sheep, or other grazing animals over a septic field is a bad idea for several reasons. Heavy animals are likely to damage the drainfield by compressing the soil and possibly by damaging buried piping. Compressing the soil over a septic drainfield interferes with soil transpiration, cutting the oxygen level needed by soil bacteria in the biomat and reducing removal of septic effluent through evaporation. There is some chance that pathogens from septic effluent may pass to and infect the animals. More about the chemical and pathogenic risks associated with plants over septic systems is discussed at Gardens Near Septics. In sum, it's better to keep livestock off of a septic field. In the photograph above we show deer grazing on a field along the Virginia Skyline Drive at Big Meadows. Deer or other wild animals passing occasionally over a septic drainfield are unlikely to cause serious damage to it.

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Planting Fruit, Vegetable, or Ornamental Gardens Near or Over Septic Systems

The short answer is it's better to keep fruits and vegetables away from septic systems, especially septic drainfields. Planting a fruit or vegetable garden over or near septic system components raises some important questions: Will there be pathogenic or chemical contamination of the soil (bacteria, viruses, cleaners) below the garden? Will septic system pathogens enter in or contaminate fruits or vegetables planted over or near the septic system? Will chemicals or salts passing through the septic system harm nearby plants? Will the garden planting itself harm the septic system in some way? The effectiveness with which the soil biomat is treating pathogens in septic effluent, the ability of the soil to filter effluent, the chemicals or salts entering the septic system, and the type of plants placed over or near the system are some of the factors that lead to answers to these questions. [The photograph above shows our vegetable garden gone wild in Costa Rica.]

• Septic effluent contains chemicals and pathogens which are potentially unhealthy or harmful to people, animals, or plants. If a septic absorption system's biomat is functioning successfully, the level of these pathogens is reduced to that of typical surrounding surface water before effluent leaves the drainfield. The "safe" distances involved depend on the soil type.
• Soil types affect how the septic system behaves and how it affects nearby plants of any kind. Clay soils release cleared effluent in perhaps a few inches but then clay doesn't perc well and is bad in general for a septic location. Sandy soils permit much greater travel of effluent and pathogens, certainly several feet. These "close" distances do not even consider what happens when the drainfield is not working well or is in failure. In that case pathogens may be released to the general environment and might travel any distance from the septic field.
• Root crops such as carrots or potato's which develop in the soil are likely to pick up pathogens from effluent in the soil over, next to, or downhill from drainfield trenches or galleys.
• Leafy crops such as lettuce or perhaps broccoli which develop above the ground but close to it may be contaminated by pathogens that splash up from the soil surface during watering or during rainfall.
• Above ground crops that grow on a raised vine such as cucumbers, tomatoes, or peppers may fare better if they must be planted over or close to septic system components, since they are higher up and less likely to be contaminated by soil splash-up.
• Salts and the septic system: Homes whose water supply is "hard" and which employ a salt-based water softener system are more likely to be passing high levels of salt into the septic drainfield. Not only does this salt risk harming the drainfield operation (mineral clogging or damage to the biomat) but such salts may also damage some plants that grow nearby.
• Chemicals and the septic system: At this website we've advised strongly against use of "magic bullet" chemical or other septic treatments as some of them are toxic and environmental contaminants. Some of these may also contaminate your garden.
• Gardening activities such as walking or digging into the first few inches of soil over a drainfield are not likely to damage it. But driving equipment such as a plow or roto tiller over a drainfield or constructing a "raised bed" garden which requires the addition of soil above surrounding ground levels can damage the system or can reduce soil transpiration thus preventing the drainfield from functioning properly. Not "functioning properly" here means that the drainfield stops successfully treating the pathogens that flow into it. It stops working and begins discharging unsanitary effluent into the environment, and into your garden.

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Planting Trees or Shrubs Near or Over Septic Absorption Systems

This is the only sort of tree that we suggest can be placed over septic system components with little risk of damage. This is actually a metal sculpture. Even the placement of this "tree" could have damaged a septic field if during its installation heavy equipment was used to deliver the tree to this spot. Real trees will damage septic components by root movement or clogging.

In this photo the light and excavated area is where the new home owner saw and dug into a smelly wet spot that appeared in the yard the morning after moving into their new home - a house built 30 years before and one which employed a home made septic tank. While there were tree roots in the drainfield pipes of the system, the septic tank itself, which was too small, never pumped, and fully blocked, was the "root" cause of system failure in this case. (Pardon the pun).

How much distance is needed between trees and septic drainfields?

Whether you are planting trees or planning a new septic drainfield, keep the drainfield or septic leach field away from trees or shrubs which are likely to put down deep or aggressive roots. The roots will quickly invade and clog the buried effluent lines and may also cause them to move, break, or become disconnected.

The actual tree to septic distance needed depends on the tree variety and its normal root growth range. Keep at least as much distance between the tree and the nearest drainfield component as the anticipated height of the tree at its maturity. So if the tree will be 30' tall at maturity keep it at least 30' from the drainfield. Some trees should be kept at much greater distances, up to 100' from septic fields, as we discuss just below.

What kinds of trees should be kept away from septic systems?

Trees considered to have deep and/or aggressive roots that are likely to damage a drainfield include:

• Bamboo, Beech trees Fagus sp. and Birch trees Betula sp.
• Cypress trees
• Elm trees Ulmus sp. and Eucalyptus
• Pepper trees
• Pine trees, such as Monterey pine
• Poplar trees Populus sp.
• Maple trees, particularly red and silver maples Acer rubrum and Acer saccharinium
• Walnut trees
• Willow trees Salix sp are popularly known for "liking water" and will certainly send out long root systems.

Kahn, Allen, Jones (book cited at Septic Systems Home-References) point out that certain of these trees such as bamboo, weeping willows, eucalyptus, cypress, Monterey pine, pepper, and walnut have particularly aggressive and deep roots. Keep such trees at least 100 feet from the nearest septic field component.

What about non-aggressive rooting trees near drainfields

Some trees have less aggressive roots and may do less rapid or less extensive damage if they are a bit nearer to septic fields. These include:

• Ornamental trees such as Cherry, Crabapple trees, and Dogwood trees.
• Other trees with less aggressive root systems such as Oak trees (red oak, scarlet oak, and white oak)
• Some Pine trees (but not the Monterey pine) and Sourwoods.

OPINION-DF: However despite some authors accepting the near-septic use of these less aggressive trees with the advice that "... their damage is likely to be less severe", any root clogging of septic systems is likely to be costly and inconvenient.

Trees near septic mound systems

Some experts (Kahn, Allen, Jones) also point out that if you're planting on the edges and lower toe of a septic mound, those plants need to be able to tolerate the higher moisture levels found in those parts of the mound system.

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Planting Ground Cover Over Septic Fields

Ivy, Pachysandra, Similar Ground Covers are NOT OK for use over a septic drainfield: these plants will reduce effluent evaporation from the mound soils and because their roots often invade and clog effluent distribution piping. The photograph shows typical ground cover north of the arctic circle in Iceland. Thick dense vegetation of any sort will conserve moisture to itself and will prevent soil transpiration. Over a septic system this means that the portion of effluent disposal that is supposed to be occurring due to evaporation will be reduced and the liquid load on surrounding soils increased - you've cut the effectiveness and shortened the life of the drainfield by such plantings. These plants are OK, however, for planting over the septic tank itself.

Wildflowers and ordinary grasses are just fine for planting over a septic system and any of its components. These are shallow-root plants that do not invade the system piping, they stabilize the soil surface, and they do not interfere with soil transpiration, the movement of needed oxygen into the upper soil layers (needed by the soil biomat below the drainfield) and the evaporation of a portion of septic effluent that enters the drainfield. [The photograph shows a field of wildflowers in northern Vermont.]

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Using Root Killers to "Un-Clog" Septic Pipes or to "Prevent Septic System Clogging"

We advise against using chemicals or caustics to "kill" tree or other plant roots which may be present in or near septic system components. People fearing that roots will clog or have already clogged their septic system piping, particularly drainfield piping, are tempted to buy these products. This is another example of a "magic bullet" that does not work, is dangerous, contaminates the environment, and is illegal in some jurisdictions. Root killers as environmental pollutants: First, using a chemical to kill or to "prevent" invasion of roots in septic piping means you are pouring toxic chemicals and contaminants into the ground water - into the environment, and possibly right into your own or someone else's well and drinking water. This is a bad idea and is prohibited in many communities.

Root killers as a magic bullet to repair a septic system: Second, if septic drainfield or other pipes are already clogged or partly clogged with tree or other plant roots, even if you killed the roots in the pipe you're leaving the clogging material.

If piping in a septic system has become root-clogged, it is often the case that not only are the pipes clogged, they may be dislocated or even broken by the growing tree roots. You may find you've contaminated the environment, left the clog in place, and wasted your money since you'll still end up digging up the clogged line to replace it. [The photograph above is a simulation of pouring a chemical into the septic system through a toilet. Don't do this.]

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Using a Roto Rooter to Remove Roots from Sewer Lines and Septic Systems

Power augers or "Roto Rooters" (TM) for plumbing drains can be an effective way to remove a blockage or clog in a drain line. But if your plumber shows you a tangle of roots when s/he pulls the augur back up the drain line, you should expect that additional repairs will be needed soon. Even if you pull roots out of the blocked pipe section, the fact that they were in there means a tree, shrub, or other plant has invaded the area and its roots remain outside the just-un-clogged pipe. You can count on the roots re-invading the pipe (and getting at those nutrients) soon. So de-rooting a clogged drain line is a temporary fix.

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Links to articles on plants or animals over septic system components:
PLANTS OVER SEPTICS
   Gardens Near Septics
   Grasses or Flowers
   Grazing, Animals
   Ground Cover, Ivy
   Trees or Shrubs
   Using Root Killers
   Using a Roto Rooter

The Septic Systems Online Book - Where Are We?

• This Chapter: SEPTIC FIELD INSPECTION
• Next Chapter: PERC TESTS
• First Chapter: SEPTIC SYSTEMS ONLINE BOOK

More expert information on this topic

More Information on Septic System Diagnosis, Maintenance, & Repair

• The Septic System Information Website home page for this topic
• Septic Systems Inspection, Testing, & Maintenance- online textbook. Detailed how to inspect, maintain, repair information
• The Home Buyer's Guide to Septic Systems
• Septic Tank Pumping Guide: When, Why, How to pump the septic tank
• Tank Location - How to Find the Septic Tank, how deep will the cover be, how to document its location
• Home & Outdoor Living Water Requirements
• Septic Tank Capacity vs Usage in Daily Gallons of Wastewater Flow, calculating required septic tank size, calculating septic tank volume from size measurements
• How Big Should the Leach Field Be? - table of soil percolation rate vs. field size
• Septic System Drainfield Absorption System Biomat Formation - what leads to drain field clogging and expensive drainfield repairs
• Table of Required Septic & Well Clearances: Distances Between Septic System & Wells, Streams, Trees, etc.

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