Got Nature? Blog

Question: We want to plant five fastigiata (upright blue spruce) in an area with heavily compacted soil with large percentage of clay content in the soil. The soil essentially feels and handles like play dough. Water cannot drain down in the soil because of the high clay content. Ewes were planted but they are dying since they are sitting in clay soil with water standing around the roots. A swimming pool was built nearby three years ago and the equipment used was rolled over this area numerous times to remove soil for the pool area, and the clay soil is heavily compacted and won’t allow water to drain.

We are thinking we will dig out the soil maybe five feet deep, 10 feet wide, and 20 feet deep and replace it with good compost top soil mix. We are not sure if we need a T drain or not. We want to plant five of the upright blue spruce in this area.

 Do you have an arborist you can suggest to come out and look at our situation?

Answer: This is a typical issue with soils in our area being composed of primarily clay which leads to heavy, poorly drained soils. The fact that there has been a great deal of construction damage worsens the problem even further. Traffic of this magnitude can render landscape sites virtually useless for any type of sustainable tree planting without mitigation. Your ideas of creating an adjusted planting space may not correct the problem completely, but may help alleviate the damage and improve planting conditions.

I am not certain that digging up and replacing the soil would be of much value, long term. I have had success with site improvements, but it isn’t guaranteed. It may provide temporary improvements to get the trees established, however, once they mature and outgrow your “prepared planting space”, the troubles could begin. Once the roots try to expand into the compacted, native soils, most likely they would be redirected back into the pit, minimizing good root spread for health and stability. Additionally, you would be creating a “bathtub effect” with poor drainage in your excavated pit.

It may be possible to remove and replace the soils in that excavated area with lateral drainage at the bottom of the planting area to remove the water and prevent prolonged exposure to wetness on the root system. Perforated tiles draining outside of the planting area may work. Create a single, central line with a herringbone lateral system that goes past the dimensions of the pit. Use good topsoil with no amendments to the new planting area. One other consideration would be roots clogging the drainage system if not set deep enough. Again, this is a stretch for mitigation, but may be successful with proper preparation.

I would suggest contacting a company with an ISA certified arborist who can assist you with the process. Use Trees Are Good’s Arborist Search to help locate an arborist in your area. Also, try reviewing the publications on construction damage for some corrective and preventative treatments for the future.

Resources:
Collecting Soil Samples for Testing, The Education Store
Soil and Water Conservation Districts, Indiana State Department of Agriculture
Certified Soil Testing Laboratories, Purdue Department of Agronomy/Extension
Arborist Search – Trees Are Good
Tree Installation: Process and Practices – The Education Store, Purdue Extension Resource Center
Mechanical Damage to Trees: Mowing and Maintenance Equipment – The Education Store
Why Is My Tree Dying? – The Education Store
Tree Risk Management – The Education Store

Lindsey Purcell, Urban Forestry Specialist
Purdue University Department of Forestry and Natural Resources