NDSU Extension - Mercer County


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Getting Old is Not for Sissies When it Comes to Trees in North Dakota

trees, drought stress in trees

Submitted by Craig Askim, Extension Agent/Agriculture and Natural Resources

Many people call and ask these questions, “Why do my trees not leaf out and have the fall colors they should have, when I water and fertilizer all year long?” and “Why do the trees look like they are dying?”. The article below addresses these questions and the answer may surprise you. In many cases doing less is better rather than trying to provide the trees with tons of water and giving it every possible type of nutrient available. 

What about trees? Is life tougher for them as they age? Even tree species that are short-lived should be able to survive 20 or 30 years.

How do they do it? The annual cycle of growth, senescence and dormancy goes on, and yet the environment is slightly different each year. How do the trees survive, and even thrive?

Admittedly, the stressful environment of North Dakota shortens the lifespan of many trees. Extremes of moisture and temperature take their toll. Just one week of flooding is likely to kill a spruce tree, although a cottonwood can handle that stress with minimal problems.

Extreme low temperatures in midwinter kill trees every year, especially those that are from seeds farther south. We often use the U.S. Department of Agriculture's Hardiness Zones as a guideline for which species or varieties might be adapted to North Dakota.

In autumn, trees go through the process of hardening to prepare for winter dormancy. The environmental cues that begin the hardening process are shorter days and cooler temperatures.

However, other factors come into play. Trees that are growing vigorously do not harden, as quickly or as much as they should. I see this every year in yards that are highly fertilized and irrigated.

The trees barely slow their growth in the fall, and they do not completely harden up for winter. The damage shows up the following spring as dead branch tips, or in the worst cases, dead trees.

So, what can we do? Unbelievably, a little bit of drought stress in August is actually a good thing. The process that trees use to respond to drought is related to the process they use to harden up in the fall.

Therefore, in giving trees a little bit of stress, we are actually helping them.

Nurseries do this every year as part of tree production. They cut back on watering to slow the trees' growth.

Should you shut down the irrigation system in your yard during August? Well, for the sake of the trees, yes. Of course, there is a tradeoff. The grass will not be quite so lush, and it might not even be green. Nevertheless, the trees will slow, and that is good. Side benefit -- less mowing!

The hardening process is also, what gives us those beautiful fall colors that we enjoy every year. Without hardening, we miss the vibrant yellows, oranges, reds and purples that nature provides.

When my wife and I bought our current home in 2013, it came with two beautiful maple trees and an irrigation system. For the first few years, the maples did not provide that brilliant fall color that we expected.

Then I realized that I had not turned off the irrigation during August. I finally remembered to do that in 2016 and the maples were beautiful that fall.

I know it sounds weird, but try stressing your trees, at least a little bit. It is good for them.

For more information about gardening, trees contact your local NDSU Extension agent.

Find the Extension office for your county at https://www.ag.ndsu.edu/extension/directory/counties.

Source: Joe Zeleznik, NDSU Extension Forester - 701.231.8143, joseph.zeleznik@ndsu.edu

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