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Elisabeth C. Miller Library

Keyword: Soil compaction

Katsura trees’ soil needs

I have some dying Katsura trees. I created a dry stream to one side of them to redirect water (they don’t like wet roots). The owner has put 1-2 inches compost/soil down for some good nutrition and a few tree stakes into the area. There is also landscape fabric (the gray kind rain can get through) and another inch of bark to stop a horsetail problem that creeps in every year.

I am wondering if the the soil around the tree roots has become compacted by rains and is prohibiting the trees from getting oxygen through their roots. The yellow is not in leaf veins like an iron deficiency usually looks; it is almost as if the plant is getting its chlorophyll drained from inside. No bugs present to my knowledge either. I would like to know both what I might do about the soil and about the trees.

Some solutions to the problem may be to take some dead branches or stems to a Master Gardener clinic and ask them to help you identify what could be happening. You may also want to check that the compost is not closer than 4 inches from the trunk of the trees. If it is, scrape it away. For further evaluation of the soil, take a sample from around the tree and send it to a lab for analysis. Our website has a Soil Testing Information section that includes a list of labs that do soil test analysis. Check the area for drainage by digging a hole and filling it with water or let the rain do it and then see how long it takes to drain away. Perhaps you have a layer of hardpan clay underneath the trees that is blocking the drainage in winter and preventing the water from getting to the roots in summer.

A great resource on Katsura trees (Cercidiphyllum japonicum) is Dirr’s Hardy Trees and Shrubs: An Illustrated Encyclopedia by Michael A. Dirr. The author notes that the tree requires ample moisture in the early years of establishment. From the book, Trees and Shrubs for Pacific Northwest Gardens, by John A. Grant and Carol L. Grant, Katsura trees prefer deep soils and adequate summer moisture. There is a Katsura planted in the Arboretum on the edge of a pond in soil that is permanently wet and it is doing just fine.

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reviving construction-damaged trees

We have some Douglas Fir trees along a ravine. There is some construction nearby, and one of the trees is looking like it has been affected. It’s losing lower branches and has much less new growth than its neighbors that are farther away from the construction. Is there anything we can do to save it?

It certainly could be compaction, though it is not possible to diagnose from a distance. However, symptoms of soil compaction damage include drooping branches, wilted or scorched foliage, and conifers dropping inner needles. This came from the Minnesota DNR’s web site, which also discusses treatment. Here is an excerpt:

“Compaction can be partially alleviated by drilling a series of two inch diameter holes to a depth of 12 to 18 inches. Begin three feet from the trunk and continue drilling holes at two foot intervals in concentric rings around the tree and continue to at least the dripline. Each hole may be refilled with sand, peat moss or mulch. Don’t recap the hole with a sod plug. There are other alternatives, such as soil injections of air or pressurized water, available from some professional tree care services.”

A WSU extension formerly available online (“Construction Damage to Trees”) explains that careful watering and fertilizing can help damaged trees, though it is best to help them before damage is noticed.

Another good resource is the Colorado State University Extension’s “Protecting Trees during Construction.”

Finally it would be a good idea to consult the Plant Amnesty referral service at 206-783-9813, or search for an arborist at the PNW International Society for Arboriculture site under “Hire an Arborist.”