Shallow rooting can be a major hazard for landscape trees. Without deep roots, the trees pose a blowdown hazard.
Causes of Shallow Rooting
Trees root shallowly either due to cultural conditions or the soil type. A lot of moisture provided constantly means that a tree never has to put down deep roots to seek out water. Instead, the roots form a mass in the top foot of the soil or so. This is a common issue in exceptionally wet climates, such as in the northwest US. It's also a problem for landscape trees planted in well-watered and over irrigated lawns. Without those deep water-seeking roots, the tree isn't well anchored.
Soil type can also lead to shallower rooting. Heavy clay soils, for example, become very dense the deeper you go. Air and moisture availability is reduced because the fine clay particles are tightly packed, so the tree mainly roots in the top of the soil. Areas with thin soil and bedrock near the surface can also have this issue, as the tree roots are unable to effectively penetrate into the rock.
Shallow Root Symptoms
You can't always look at a tree and instantly tell that it has a shallow root system. The most obvious visible symptoms usually only surface once the roots are no longer anchoring properly. The soil around the base of the tree may look disturbed or churned up after a windy day, which results from major tree movement. Trees may also begin to lean as they become too large for the shallow roots to support.
Mass amounts of large, knobby surface roots can also indicate shallow rooting. All trees have some surface roots, but they shouldn't completely overtake the ground below the tree. Another symptom is if the tree can't handle even slight water stress. If several days pass with no irrigation or rain and the leaves begin to wilt, then shallow roots may be insufficient for providing enough water for the tree.
It's very difficult to save a tree with shallow roots. With younger trees that are rooting shallowly mainly due to locational reasons, you can encourage deeper root growth by watering deeply and less frequently. It's also a good idea to stake the tree for a season or two until the roots become deeper and more secure.
Unfortunately, it is usually best to remove mature trees if they have shallow roots. This is especially true if you have seen churned soil or other signs of movement from the tree. It can be in danger of blowing down, which can cause damage to your home or cause injury to anyone in its way.
Contact a tree removal service in your area if you have a large tree with dangerously shallow roots.