The highly plastic clay soils common in the Midwest will exhibit shrinkage when subjected to drying conditions and expand when over saturated. These types of soils will substantially reduce in volume as the clay dries out. This drying phenomenon is often referred to as desiccation. Desiccation can occur following extended periods of hot, dry weather and is often exacerbated or accelerated by the presence of large trees and shrubs.
One way to spot desiccation is to inspect the soil where it meets the foundation of your home or the edges of the concrete driveway or sidewalk. When the soil is shrinking away from these it will create a gap in between the soil and the sidewalk. This is a telltale sign that your yard needs more water.
Trees with root system that extend both vertically and laterally can reduce the moisture content of soils that support a residential foundation system, resulting in a reduction in volume of foundation support soil. If large trees are present in close proximity to a home, it becomes double important to maintain an ongoing watering program to minimize the effects of desiccation.
When planting trees and shrubs, it is important to remember to plant them farther away from the home itself. First, remember that a small tree or shrub will grow to be a large tree or shrub. Know what type of tree or shrub that you are planting and how big it will get. Secondly, remember that the root system of the tree will end up larger than the tree itself. Plant trees far enough away from the house so that it’s root system will not grow close to the structure and draw moisture away from soils near the house.
A tree’s root system is much larger than most people realize. The root system of a tree will grow to be over twice the size of the tree’s canopy in most cases. This means that a tree may seem like it is far away from the house, but in reality, its root system is quite close. These roots draw significant amounts of water from the soil drying it out. This can impact the soil that supports your home’s foundation or concrete pavement.
Even during normal weather conditions a lawn and landscape should be watered to keep the soil from shrinking, but during drought conditions it becomes even more important. Drying clay soil like the type we see in the Midwest is especially susceptible to shrinking. Iowa, Nebraska, Missouri, and Kansas all have varying degrees of clay soil and all are known for problems that result form expansion and contraction of clay soil. Maintaining appropriate moisture levels in the soil can help reduce the risk of foundation problems.
Another reason it is important to plant trees away from your house is to prevent concrete heave. If you have trees planted near your driveway, sidewalk, or patio, the root system can actually grow under the concrete and begin to push the concrete up. This creates trip hazards and can cause cracks in the concrete. Often times, it may appear that the concrete around this area is sinking, when in reality the concrete is heaving due to pressure from the tree roots.
While trees and shrubs add extra curb appeal, structural damage and concrete issues will not. It is important to take all of this into consideration as you develop your landscaping plan.