JoAnne Skelly: Waterlogged or deeply watered?

My friend Sandie asked me a good question this week, “Is all this moisture good or bad for trees?”

If you have read my column for a while, you know I preach repeatedly that trees need watering all year, including the winter. If precipitation doesn’t come as rain or snow, we have to drag out hoses or turn on irrigation systems. However, this year we have had an abundance of water in the form of long-lasting snow. What started as rain at the end of December quickly turned to snow and has remained on the ground, since then.

My answer to Sandie is the typical horticulture answer, “It depends.” The factors that influence whether all this wet is beneficial or harmful for trees include soil type, tree type, age, and health of the tree. Soils range from sand to clay with many variants in between.

Here at our house, the soil is sandy and drains well, so we don’t have standing water. Our trees should thrive in the spring with lots of lush new growth. Yet, just five acres away, our neighbor’s lot is covered with standing water. Not only does their clay soil have almost nonexistent drainage, they also have an artesian spring that has been overflowing all winter. This increased amount of water in addition to the snow load may mean trouble for their trees. Roots may rot causing trees to decline, and, in some cases, die. When roots rot, a tree can no longer take up water even when water is available. Also, when roots rot, trees can become unstable in saturated soils, topple in storms, and die. Compacted soils cause a further problem when saturated because drainage and airflow are minimal.

Certain types of trees handle wet feet much better than others. Poplars (cottonwoods), willows and birches thrive on the extra water. Pines, spruces, and other evergreens will not do well in soggy to saturated conditions. Young trees don’t have the number of roots that old trees have and are more likely to suffer.

Fewer roots mean getting less oxygen out of a wet soil, where all the soil pores are filled with water. Growth of a tree canopy and of its roots requires oxygen. Oxygen deficiency is a major cause of decline and reduced growth when soils are saturated.

Tree vigor prior to this overload of snow and water will influence how a tree responds to the stress of saturated soils. Trees stressed by drought or insect infestations over the last few years are less likely to thrive. We just have to wait and see.

JoAnne Skelly is Associate Professor & Extension Educator Emerita at University of Nevada Cooperative Extension. Email skellyj@unr.edu.