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Wednesday - February 03, 2010

From: Heber Springs, AR
Region: Southeast
Topic: Septic Systems
Title: Tree roots vs. leach field in Heber Springs AR
Answered by: Barbara Medford

QUESTION:

We need shade in front of our west facing house; however, our septic system and leach field are there also. What kind of fast growing trees can we plant that won't ruin our septic system?

ANSWER:

We are assuming you had no choice either in the orientation of your house or the location of the leach fields. Which direction a house faces is determined by where the street is, and leach fields must be placed where the soil drainage is appropriate. Unfortunately, all the research we have done on what to plant over leach fields has indicated that grasses, with their fibrous roots to help prevent erosion, are the best thing to use, and woody plants, including trees and shrubs, are the worst.

So, that's the bad news—plants require water, lateral lines have water, so plant roots are going to grow towards the water.  The roots of woody plants will seek a way to get as much water as possible and will make their way into the lateral lines and clog them.  The further away the plants are from the lateral lines, the longer it will take them to get there and begin growing in—but they will eventually get there.  A brochure from the Metropolitan Sewer District of Cincinnati recommends rodding (inserting a flexible cable with a cutting tool on the end into the line) once a year to clear the lines of any roots that have grown into it. You can try that kind of delaying tactic and hope that you move away before real damage is done. That won't make the next resident very happy, and perhaps you plan to stay on your property for many years.

However, we are going to answer your original question about selections of shade trees for your west-facing house. We are frequently asked for trees with taproots under the mistaken impression that the roots will only go down. While there are trees that have taproots, they also develop spreading roots, again to get moisture and nutrients nearer the soil surface. You asked for fast-growing trees, but remember, the faster that tree grows, the roots underground are growing even faster, and fast-growing trees are usually short-lived. You will have to make your own decision, based on where your lines are, on where to plant trees. It's likely that by the time any tree gets tall enough to offer shade, the roots will have extended to the septic lines. Follow each plant link to our webpage on that tree to learn how much water it needs, how fast it grows, whether it's evergreen, etc. We selected several oaks that are said to be "moderately fast-growing," and are good shade trees.

Trees native to Arkansas:

Juniperus virginiana (eastern redcedar)

Pinus virginiana (Virginia pine)

Platanus occidentalis (American sycamore)

Quercus alba (white oak)

Quercus coccinea (scarlet oak)

Quercus macrocarpa (bur oak)

Quercus palustris (pin oak)

Taxodium distichum (bald cypress)

From our Native Plant Image Gallery:

 

 

 

 

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