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Many ash trees in the Denver Metro area are not faring well. Some trees have scattered dead branches, while others appear at least half dead. Some are prematurely dropping leaves.
While examining samples in our clinic and in the field, we’ve found that growth increments are shortened for the past 3- 5 years or more. I’ll explain what that might mean momentarily, but first I want to explain what growth increments are and how to look for them on your own trees.
Growth increments indicate the amount of growth a plant makes each year. The distances between what look like “wrinkles” on the stems are growth increments. To find them, start at the tip of a branch and move inward along the branch until you find the first set of wrinkles. This distance is how much growth your tree put on this year. Travel inward from that point until you reach the next set of wrinkles. That’s how much growth the plant made last year. You can continue to travel back in time and see how much your tree has grown. For many species, growth of anywhere from 6 to 10 inches is ideal.
Short growth increments can have several interpretations. If an established tree has shortened increments, something is stressing it. That’s why it hasn’t been able to grow much. Stressors in our climate include soil compaction, soil oxygen starvation, poor soil drainage, dry soil and/or construction activities that have damaged roots – to name a few!
Short growth increments are normal for a few years following transplanting. Trees spend their energy regenerating their root systems after transplanting, so they don’t develop much above ground. Certain species, such as pinyon and bristlecone pine just don’t grow much each year.
Shortened growth increments can also be the result of injury from hail, weed whackers, lawnmower dings and insects or disease. All of these can damage conductive tissue under the bark which interferes with the nutrient and water flow and results in poor growth.
“Ash decline” describes what is happening to many of our trees. The term is used to describe a problem that has more than one cause. In our geographic area, ash decline is believed to be the result of a combination of factors such as the poor soil conditions mentioned earlier, the drought and this year’s soggy soils. Insects are often part of decline as they are attracted to stressed trees.
What can you do to help? Prune out dead branches or remove badly-damaged trees. If fall and winter are dry, apply water to the root zone of trees monthly from Nov 1 to March 1. Apply nitrogen fertilizer to the root zone next spring at the time of leaf expansion