Q. I would like to plant some trees in my yard, but am worried about their invasive roots clogging my sewer line. A neighbor of ours in the old neighborhood had a clogged sewer line and found the roots from a large Silver Maple tree were the problem. Also, it seems that my township forbids planting weeping willows because of this sort of potential problem with clogged sewer lines. Can you suggest any trees that have "well-behaved roots" and are less likely to cause a problem with my sewer line?
A. Tree roots cannot break their way into intact sewer lines -- not even weeping willows. The problem occurs when old terra cotta pipes crack or develop leaks at the joints. The roots of almost any tree will take advantage of the situation and could wind up clogging the lines. This is much less of a concern in newer developments because now builders use PVC pipe, which is much less likely to crack and invite an invasion of roots.
Most tree roots are confined to the top twelve to fifteen inches of the soil, where there is adequate moisture, oxygen and nutrients to support a tree's growth. The fine, hair-like feeder roots responsible for absorbing water and nutrients from the soil extend out two to three times the reach of the branches (also known as the tree's dripline).
We used to believe that tree roots were a mirror-image of the top of the tree, but research has shown that tree root systems are much shallower and broader spreading than that.
Smaller trees such as crabapple (Malus spp.), Japanese maple (Acer palmatum) and 'Winter King' hawthorn (Crataegus viridis), or large shrubs such as bottlebrush buckeye (Aesculus parviflora), quince (Chaenomeles spp.), and blackhaw viburnum (Viburnum prunifolium) would have less extensive root systems than very large trees such as Norway, silver or sugar maples (Acer spp.), willows (Salix spp.) or oaks (Quercus spp.). Willows and Silver Maples are sometimes called 'water seekers.'
You should be more concerned about doing a thorough assessment of your planting site so you can chose trees that will grow well in those conditions. The factors to consider should include:
• How much sun or shade they will have to tolerate.
• Soil texture and structure. Is your soil compacted clay or clay subsoil, or is there some topsoil?
• How well the site drains. Does water pond on the surface after a rain?
• Does the site maintain adequate soil moisture or does it tend to dry out quickly?
• Will the trees be exposed to road salt?
• Are they near concrete sidewalks, driveways or buildings with concrete foundations or mortar joints? Calcium carbonate leaches out of concrete and may raise soil pH (the measure of acidity or alkalinity) to a range that limits your ability to grow trees that prefer an acid soil. These include maples, oaks, dogwoods, magnolias, conifers, and broad-leaved evergreens such as rhododendrons and hollies.
• Exposure to wind, especially in the winter. Wind is hardest on broad-leaf evergreens.
Once you have assessed the planting site, then you can narrow the list of possibilities to those tough, durable trees that do not have major insect or disease problems that would require your constant attention to keep your chosen plants healthy.