Q: Which has the deepest, most invasive roots, a 30-foot maple tree or 7-foot cedar hedges? We had tree roots in our sewer lines and were told they’ll continue to grow. We dug down 6 feet and found hair roots and a few roots 1 inch in diameter.

A: Root intrusion into drainpipes keeps a plumber friend of mine very busy replacing broken sewer lines.

The sewer pipes used in new home construction for the last 20 years or so are made of black plastic pipe put together with glued joints. That type of joint almost never leaks. Before that, however, it was quite a bit different, and therein lies the problem with roots and sewer systems.

The most common sewer line construction before plastic was either terra cotta clay pipe or tar-impregnated paper called Orangeburg pipe. The clay pipe has a fitting with a gasket, and the Orangeburg was put together with a slip joint. Over time, both types begin to leak water and sewage into the soil near their junctions, creating a very rootfriendly environment.

The vast majority of roots in most landscape planted trees are in the top 12 inches of soil, which is about as deep as the water from a yard irrigation system usually saturates. But there are always a few very small roots that explore deep and wide, trying to find water. These are the little demons that create all the problems, because once they find a good source of water and nutrition, like a leaking sewer line, they think they’ve won the lottery.

This scenario is possible with most landscape trees regardless of species.

With clay pipes, roots will find their way into the sewer lines through the coupling area when the gaskets degrade. Small roots also get into Orangeburg pipes that have leaking slip couplings, but larger roots can punch through the side of the tar and paper material, causing the line to collapse. If that happens, you’ll need a sewer specialist to repair your system. Speaking from my own experience, it can be expensive.

As the roots flourish in the nutrient-rich interior of the pipes, they begin to restrict the flow of water and other materials. Sometimes a plumber can use his rooter cutting blade on his sewer snake to cut the small roots and keep the line functional. But if the fine roots have enlarged to the point where no cleaning device can remove them, they often crack the line and make replacement necessary.

If you have a tree growing near your sewer line and you’re worried about root blockage, you can have a plumber come out and locate the line. At the very least, have him run his rooter snake all the way out to the city main line. If he runs into small roots and cuts them, at least you have the problem taken care of for this year.

Once your plumber cuts the roots, it’s smart to stay on top of the situation by having him come out every year to clear the line. This ongoing maintenance is much less expensive than a complete sewer line replacement.

By cutting small roots before they become a large problem you can eliminate the possibility of your sewer line backing up into your tub and shower.

David D. Mortimer is a certi fied arborist with more than 30 years’ experience. E-mail questions to dmortimer@theacorn.com.