So will evergreen roots get into your sewer line?
Here's the deal. Most tree roots occur in the top three feet of soil and most of them are in the top 18 inches.
Tree roots are in direct competition with turf and other plants for moisture and that is why they occur in the top of the profile naturally.
Tree roots require oxygen and oxygen becomes less and less available the deeper you go into the soil.
In a built environment some soils have been altered and oxygen becomes more available deeper in the soil because of improper compaction or granular backfill material over top of water and sewer pipes.
Root tips are microscopic in size and can be squished into oblivion between your fingers.
Roots do not break pipes or make holes in pipes.
Roots are geotropic meaning that when they encounter an obstacle in the soil they grow around it and not through it.
Tree roots can spread three to four times the width that the above ground branches are spread.
Tree roots will unnaturally go to eight to 10 feet deep in a granular soil backfill because oxygen is available.
Some of those who install sewer and water lines prefer backfilling with sand because there is less settling and fewer call backs for a settled trench in your front yard.
Sewer pipes over the years have been constructed of many different materials - clay, asbestos, concrete, cardboard impregnated with wax and more recently PVC plastic. I believe the engineers have now got it right and are using the right pipe material. Going forward, tree roots in sewer pipes will become less and less because there are fewer joints, less leakage.
Tree roots enter sewer lines where the pipe is compromised already. Perhaps it was damaged at the original backfill or in the instance of clay pipes and some of those other materials, there were several unsealed joints in the sewer line.
If you think about this, there is nutrient rich moisture weeping out of these joints in the pipe available to a tree root that normally wouldn't be that deep in the soil
There is more oxygen down here that is entering the sewer pipe from the house and being released through the compromised sewer pipe.
What has been created is a perfect root growth environment - moisture, oxygen, nutrients. With these kinds of inputs available to the plant (tree's roots) a proliferation of fibrous roots develop through either the already broken pipe, or the unsealed pipe joints and cause either a slow draining sewer or complete blockage.
In my experience and through what I have seen or heard about, there are no woody roots ever found in sewer pipes, always fibrous.
So in conclusion:
If roots are in your sewer pipe, chances are the pipe is old and worn out, or broken, or constructed of one of the inferior products of the past and is leaking;
You can't be sure it was your chokecherry or your neighbour's elm because roots can travel three to four times the branch spread of the tree;
Some tree species are more aggressive rooters than others as indicated by their size and winter hardiness;
The only root growth element that naturally occurs at the depth of a sewer line is moisture, which naturally percolates and wicks up through the soil profile to the natural root zone of trees. The oxygen and nutrient availability and the creation of an environment suitable for root growth is a product of the built environment and historically inferior sewer pipe material;
And finally, yes evergreen is a good choice. It is likely the roots from an evergreen will never be in your sewer pipe. Something to consider is thatthere are many unused evergreens that are more suited to suburban yards than the traditional Colorado spruce. Swisstone pine , limber pine and Norway spruce are some choices to consider as they are slow growing and their stature at maturity is smaller than the Colorado spruce.
