Question
QUESTION: I Live in western washington st.  I am considering planting some Birch trees in my yard.  However, my sewer line (4" PVC  the kind with the rubber gasket connector) will be about 4ft. away from where I plant the trees.  The sewer line is about 1.5ft below the surface.  I am worried about the roots messing up my line.  Is this a concern? What is your advice?
Thank you.

ANSWER: Birches and sewer lines do not mix well. Trees and shrubs are much riskier choices for the drainage field than herbaceous plants. The woody roots of these plants are more likely to clog and damage drain lines. The root system is in the first 2 feet or so of the soil and will seek water. I would   keep the trees at least 20 feet from the lines.

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QUESTION: I am also considering a the Hornbeam.  How are their roots with a sewer line?  I don't have a septic system or drain field; it is just a 4" sewer line that runs from my house to the cities main line.

Answer
As long as there is not leak in the sewer line the roots will not be a problem. Roots will seek out water and invade the pipe IF there is a leak. The newer sewer lines are sealed and should not be a problem. Of course you will not want to plant right on the line so there will not be a chance to hit the line while digging the plating hole. I do not think you will have a problem in this case.

Hornbeam Carpinus caroliniana is very similar to birch--they usually grow in  a more moist soil near streams and stream bottoms. This tree, also sometimes called "Ironwood," and the Eastern Hophornbeam. I think a better suited tree for yards is Hop Hornbeam, Ostrya virginiana. As you can see we sometimes get mixed up when using common names.

Hop hornbeam is a small tree, typically reaching a maximum height of 30 feet with a proportionally short, straight trunk of 1 foot in diameter. The crown is broad and rounded or vase-shaped. Hop hornbeam is a common tree throughout the eastern United States in a variety of habitats from stream banks to upland woods and dry, rocky slopes and ridges.

European farmers used relatives of the hop hornbeam to make yokes for oxen, from whence the name "hornbeam" arises. These trees were also referred to as "yoke-elms."

Hop hornbeam is sometimes confused with ironwood (Carpinus caroliniana), also known as blue beech. The latter has a very smooth gray trunk that has a "muscular" appearance (hence the name ironwood), whereas hop hornbeam has brownish, grooved, and scaly bark. Nonetheless, the term ironwood is applied to both the hop hornbeam (Ostrya virginiana) and the blue beech (Carpinus caroliniana) in some texts.

Hop hornbeam serves well as a landscape tree owing to its tolerance for very dry soils and shade, as well as its ability to live in a stressful urban environment.