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Friday - August 26, 2011

From: Austin, TX
Region: Southwest
Topic: Compost and Mulch, Planting, Transplants, Shade Tolerant, Trees
Title: Replacing mature Arizona Ash trees in Austin
Answered by: Barbara Medford

QUESTION:

Mr. Smarty Plants, I have 2 very large, very old Arizona Ash trees in my yard. I want to remove them and replace them with something like Cedar Elm or Chinquapin Oak. The problem is that they are the only thing providing my house and yard with shade, so I'm hesitant to remove them until I absolutely have to. Can I go ahead and plant the new trees this fall so that they can get some height before I have to remove the others? If yes, how close can I plant them to the old trees? (The old trees are really in the perfect spots in our small yard, so I want the new ones as close as possible.)

ANSWER:

We have thought about this for several days and can come up with no good solution. The roots of your mature trees should be extending out two to three times the distance to the edge of the shadeline from the trunk. You say your yard is small and the existing trees are in the perfect spot, which is to say, the only spot for a large shade tree. We are also assuming that if you have any ornamental plants in that area, they need shade. We have seen examples of areas where a large tree was unexpectedly cut down or blown down by a storm, and all the shade plants beneath it suffered. If you try to dig holes to put in new trees near the old trees, you will damage the roots of the old trees, maybe even to the point of killing them. And you will be asking the delicate roots of the new tree to suddenly compete with the more established, and thirstier, old roots. That's kind of a lose-lose solution; you could end up with no trees at all.

According to this USDA Plant ProfileFraxinus velutina (Arizona ash) does not even grow natively to Travis County. As its name implies, it is more a desert plant, but with our current weather conditions your trees are likely feeling right at home. The Arizona Ash is often victim to borers and verticillium wilt, resulting in being somewhat short-lived.

However, if the trees do not seem to be in imminent danger of dying, we would suggest you hold onto them as long as feasible. In the meantime, if you do, indeed, have shade-loving understory plants, we would recommend transplanting them during the Fall and early Spring to other shady spots, or accepting that you will likely lose them. If you decide to go ahead and take out the old trees, that could be done now or in the Fall but you need to then do extensive preparation for the new trees which should be planted in January, when they are more dormant.

This extensive preparation should include the engaging of professional arborists who can get the trees down without undue damage to your house or other plants. Next, have the ash roots ground out, for at least as far out as your arborist estimates the hole for the new trees will need to be. While you will probably want to have any large root pieces removed, the ground remnants will serve as a good compost in the soil, and help improve drainage, always an essential in our alkaline clay soil. We again advise that you take the advice of the arborist on preparation of the soil and size of the hole.

Now, about the new trees, whenever you plant them. Again, plant in the Winter, and do not buy the trees until you are ready to plant. There are always sales on trees in late Summer or early Fall, but they have likely already been out of the ground and in a pot for months, and will have to wait there more months for the appropriate planting time. This often results in roots growing round and round in the pot, which can strangle the tree. We looked at our webpage on both the trees you mentioned as replacements; follow the links to read more information on each tree.

Ulmus crassifolia (Cedar elm) - nicely proportioned, drought tolerant

Quercus muehlenbergii (Chinkapin oak) - relatively fast growing and free of diseases and pests

 

From the Image Gallery


Chinkapin oak
Quercus muehlenbergii

Cedar elm
Ulmus crassifolia

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