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This article describes the types of trees, shrubs, or similar 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.
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Planting Guidelines for Septic Drainfields, Mounds, Raised Beds, Septic Tanks and other Septic Components
Planting fruit trees, or vegetables (or anything else edible) over the septic drainfield might produce food that is unsafe to eat: see SEWAGE CONTAMINANTS in FRUIT / VEGETABLES for details.
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 farthest away from septic systems?
Trees considered to have deep and/or aggressive roots that are likely to damage a drainfield include:
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.
Can I Plant Non-aggressive Rooting Trees near Septic 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:
OPINION-DF: Some authors accept the near-septic use of these less aggressive trees with the advice that "... their damage is likely to be less severe". This seems silly to me. Any root clogging of septic systems is likely to be costly and inconvenient.
If you have a shrub for which you have reliable knowledge about the maximum extent its roots will normally reach, you might think it’d be ok to plant it exactly that distance from the nearest drainfield trench.
But I’d be careful: the extra levels of nutrients delivered to the soils by the drainfield may attract roots from nearby trees or shrubs and cause them to travel farther than usual.
OPINION-DF: I’d keep shrubs with a “known” root travel distance at least 25% farther than that "known root travel distance" from the edge of a drainfield.
Guide to Planting 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.
In the photo at the top of this page, our field in northern Minnesota provided ample room to place septic system components more than 100 feet from the nearest tree. But what about those tire track that show up in light snow? Driving over the drainfield can also damage it.
Shrubs or Trees Recommended as Suitable for Planting Over / Near Evaporation-Transpiration Septic Systems
The following table of native (to New Zealand) or introduced species of shrubs and trees lists species that are considered suitable for planting over an evapo-transpiration system and should be acceptable over a mound system or conventional drainfield as well. Note that other native species local to your area might also be suitable.  Separately at Grasses or Flowers we provide a similar table of suitable grasses.
Frequently Asked Questions (FAQs) about recommended distances from septic drainfields to various trees and shrubs
Question: septic distances for Norway Pines & Red Spruce Trees?
Have you any information on Norway PInes and Red Spruce as i have these planted in my yard and am concerned about there potential damaging effects on my septic system......... thanks.... they r only 4 feet so far so i can transplant them if need be - Will Treeman (4/11)
Reply: 40-60 feet for a 20-40-year early tree-life range, longer for longer tree life expectancy
Tree distances to septic drainfield for red pine / Norway pines
According to Pennsylvania State University "The red pine is a native North American tree species sometimes erroneously called the "Norway pine". ... Red pines grow very rapidly for their first 60 or 70 years of life. They can live for up to 350 years and reach heights of 120 feet and diameters of up to three feet. " 
Using a 60-year planning time frame, and our rule of thumb for distances of normall-aggressive-root-system trees from septic drainfields, assuming a 60-foot tree height, I'd keep my red pines (or "Norway pines") sixty feet away from the drainfield. 100 feet would be safer as pines can have aggressive root systems.
Tree distances from septic drainfield for Red Spruce.
According to the University of Maine's Maine Tree Club, "Red spruce can attain a height of 60-80 feet and a diameter of 1-2 feet. It will occasionally exceed these measurements." Synonyms for red spruce include Yellow Spruce, West Virginia Spruce, Eastern Spruce, He-Balsam" Picea rubens, 
So the same rule of thumb as for red pines applies: if you don't want the trees to ever threaten the septic drainfield for the next 30-60 years, promising the trees a long and happy life, keep them 100 feet from septic drainfields.
Note: guessing at the tree root area and health for red spruce is complicated by soil chemistry and nutrients and so guessing root area size based on canopy size is less reliable for this species. 
Questions & answers or comments about recommended distances from septic drainfields to various trees and shrubs.
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.