In the Garden | The enemy of my garden enemy

Tim Smith

The advertisement in the back pages of the magazine said the tree for sale was a fast grower and would provide shade in just a few years. It was hardy and beautiful, and resistant to disease.

The picture at the top of the advertisement illustrated a large, spreading tree with happy people picnicking in the shade. Then I saw (in small print) that the tree was Ulmus pulmila. Just Ulmus pumila, no mention of the common name: Siberian Elm, or what is commonly called “Chinese Elm” around here. (There is an elm species truly identified as “Chinese Elm,” Ulmus parvifolia, which is not the one we grow around here.)

A client, who has spent great effort and expense removing several Siberian Elms from his yard, came into the WSU Extension office to ask about the trees in this advertisement. He said they looked like a promising replacement for the trees he had removed. I’m glad he asked before planting.

Siberian Elm are found in many yards around Eastern Washington, planted because they thrive under our conditions, but mostly because they are inexpensive to grow from seeds, rather than the more expensive methods used to propagate most of the ornamental trees that you see around here.

They are so easy to grow that you will have thousands of seedlings from the half million seeds produced yearly by a mature tree growing in your yard. The seeds are produced about June and drift in the wind for as far as the wind blows. They are a serious weed, because they, if not removed promptly in the first year of growth, set deep roots and become difficult to pull.

They are also the host to some of the most common insects people bring to the WSU master gardeners clinics. In the late spring, huge populations of elm seed bugs build up, feeding on the green seeds, then migrate into people’s homes, and, though they are seeking only shelter and do no damage, people resent their presence.

As the summer advances, the tree supports huge numbers of elm leaf beetles, which eat holes in the leaves, leaving a window pane of tissue in the hole. Populations are sometimes high enough to almost defoliate the tree. Unfortunately, the tree survives the loss of leaves. These beetles, which are olive brown with a double dusky-yellow stripe running down the back, also enter people’s homes as unwelcome guests.

While I’m on the subject of bad trees, another fast-growing tree that may be advertised in the pulp magazines is the grossly misnamed “Tree of Heaven” (Ailanthus altissima).

This tree is certainly fast in growth, but it has the nasty habit of self-seeding and showing up spontaneously, establishing itself in non-maintained areas and becoming difficult to eradicate. They are generally pest free but are reputed to be the favorite tree host of the newly introduced brown marmorated stink bug, which loves to shelter in your home, and they will not be pleasant guests. They are not called stink bugs for nothing.

Most of the time, if the advertisement mentions “fast growing” as a characteristic of the tree, that should tip you off that the tree will be messy or short lived, or both. Shop for trees in local nurseries after you study its appearance and behavior. The WSU Master Gardeners have people who can help you on this subject. You can reach out to the group by calling 667-6540.


A WSU Master Gardeners of Chelan County column appears weekly in The Wenatchee World. Tim Smith is one of four columnists featured.