Ash Decline

Question:

 I have an ash tree that was planted 21 years ago. In the last year or two it has started to lose its leaves. There are numerous bare branches and many fall off.

The leaves that do come out are a mix of healthy green ones and then many others that have yellow spots on them. Planted around the base of the tree is a ring of sedum. There are some very large roots of the tree growing near the surface of the yard. The soil is mostly clay. I am afraid that I will lose this tree. There are one or two others in the neighborhood that have the same look. They were all planted by the developer when the homes were built.

Minnesota Master Gardeners say:

 The growth pattern indicates that the tree is under stress and in decline. In the absence of an on site inspection it is difficult to pinpoint exactly what is going on. However, some possible causes are listed below.

One possibility might be that the trees were planted too deeply, a condition that is observed frequently. This can result in stem girdling roots. The roots start encircling the main stem, cutting off water and nutrients to the tree. In addition, the trees may have been root bound at the time of planting which in time can also lead to stem girdling roots. A University of Minnesota fact sheet on stem girdling roots is available online at: http://www.extension.umn.edu/distribution/naturalresources/DD7501.html

It also might be a case of compacted soil at the planting site. This is common on heavy clay soils and especially so in new housing developments where heavy equipment has been used to do the final grading. Trees planted in compacted soils fail to grow due to poor root penetration into surrounding soils and subsequent low water and oxygen uptake by the roots.

Disturbed soils, another condition common in housing developments, often contain low levels of plant nutrients resulting in poor plant vigor. The trees are under stress and are then subject to attack by disease pathogens and insects, often resulting in the death of the tree. Having a soil test done at the planting site is recommended prior to planting. Information on soil tests, how to obtain soil sample bags, how to take the sample and where to send the sample for testing, is available on line at http://soiltest.coafes.umn.edu/Lawn/garden.htm

The following University of Minnesota web site, Tree Planting 101, will also be of interest:
http://www.cnr.umn.edu/FR/extension/TreePlanting101/101intro.htm

It would appear that the tree is well into the decline cycle and it would be difficult to save. However, if this is a particularly valuable tree, you might want to consult with a professional arborist, certified by the ISA, the International Society of Arboriculture. The Minnesota Society of Arborists listing is available on line at: http://www.isa-msa.org/