Root System on Lilac
Lilac roots aren’t considered invasive and as long as you leave enough space between the tree, or shrub, and the structure, there is little risk from planting lilacs near foundations. Lilac roots generally spread one and one-half times the width of the shrub. A distance of 12 feet (4 m.) from the foundation is generally enough to prevent foundation damage.
Potential Damage from Lilac Roots
It’s very unlikely that lilac bush roots will break through the side of a foundation. Damage usually occurs when lilac roots approach the base of the foundation under the soil. Since lilac root systems are shallow, they can only reach the base of shallow foundations. If you have a deep foundation, there is little risk of damage. Another condition for foundation damage from lilacs is a heavy soil, such as clay, that swells when wet and shrinks dramatically when dry. During periods of drought, the feeder roots pull a lot of moisture from the soil at the tips, causing it to shrink dramatically, and cracks in the foundation may occur. The soil swells again after a drenching rain, but the cracks in the foundation remain. In situations where the foundation is deep and the soil is light, there is little chance of damage to foundations, regardless of the distance between the foundation and the shrub. There is a small risk of damage from lilac roots to water and sewer lines. Lilac roots follow sources of nutrients and water along the path of least resistance. They are likely to penetrate water and sewer lines that leak, but unlikely to break sound pipes. If you’ve planted your lilac shrub 8 to 10 feet (2-3 m.) from water and sewer lines, however, there is little risk of damage, even if the pipes have cracks.
