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You Can Take the Birch out of the Forest But… (06/22/17)

Birch trees are found in cool northern forests where the soil is slightly acidic.

You Can Take the Birch out of the Forest But…

Birch trees are found in cool northern forests whereJohnson.1 the soil is slightly acidic. We find paper birches naturally in the Turtle Mountains and the Pembina Gorge, for example. In the forest, a layer of leaf litter protects birch roots from grass competition and keeps the soil cool and moist. A birch in the city, however, may live under much different conditions. Beautifully landscaped yards with well-manicured lawns are a harsh climate for a birch tree. When stressed by these conditions, birches will be attractive to the bronze birch borer, birch leafminer, a yellowing called chlorosis due to basic (high pH) soils, and to dying back because of moisture stress. Such stressed birch trees often die from the top down, leaving a homeowner wondering whether to prune or remove the tree.

Although many birch trees succumb to bronze birch borer every year, even more are reported with moisture stress. If a birch tree still has more than half of its leaves, you can improve its growing conditions by providing a more forest-like environment for its roots. If you are planting a new birch tree or even replacing an old one with another birch tree, follow these recommendations.

  • Deaden the sod in a wide circle around the tree and replace it with 3-4” of organic mulch (wood chips). The mulch will decay and return organic material to the soil, and will need to be refreshed periodically. To deal with weeds and grass that will become established in the mulch, spray the weeds with glyphosate. Mulch will cool the soil and help keep moisture in the rooting zone. It will also reduce heat build-up. After applying the wood chip mulch, pull it back from the trunk a few inches to keep voles away from the trunk.
  • Avoid using weed and feed type fertilizers within about 25 feet or so of the tree. These contain broadleaf herbicides that trees can take up through their roots, causing additional stress.
  • During dry periods in the summer, water deeply. This is best done with a lawn sprinkler since tree roots will extend out farther than you think. There is a concentration of feeder roots at the tree’s drip line, but roots will extend at least as far as the tree is tall, and usually farther. You will not only be adding moisture, you will be cooling the root zone.
  • Bronze birch borers leave little D-shaped holes. Inspect the main trunk and larger branches for these indicators of bronze birch borer. If a birch still has more than half of its foliage, both systemic and spray treatment options are available. Treatments are only effective when the tree is in the early stages of infestation.
  • Birches with yellow leaves are usually suffering from a lack of iron or manganese or both. These elements are not in short supply in the soil, but are simply not available to the tree when the soil is very basic. Replace these trees with non-birch and non-maple species that can tolerate more basic soils.

Lezlee Johnson

North Dakota Forest Service

Forest Health Manager

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