Caring for Trees in the Lost River Valleys

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By Chad Cheyney, Butte County Extension Educator





Give your trees a break! Proper timing, amount and application of water to trees in the Lost Rivers Valleys are the key to keeping our trees out of trouble with winter injury, diseases and insects. Properly irrigated trees successfully repel most insect and disease problems. Trees stressed by inadequate amounts or improper timing or poor placement of irrigation water are stressed and become increasingly susceptible to a wide variety of insect and disease complexes. While it may be possible to correct insect and disease problems in the short term by application of pesticides, in the long term, only proper irritation will keep our trees healthy. Your trees need at least twice as much water as the same area of grass!

If you look over the vast area of central Idaho and the Lost River Valleys, one is impressed by the wide-open spaces and unobstructed views that one gets from almost anywhere. This doesn’t happen in the Appalachian Mountains. The difference is trees, lots and lots of tall trees. We have quite a bit of woody vegetation, but most of it is about three feet tall and grey green. The main difference between these two ecosystems is the amount and distribution of water.



While the 6 inch spruce seedling you received on Arbor Day gets along pretty well with 1 gallon of water a week, a mature spruce tree with a 20 foot branch spread (drip-line diameter) requires 32 gallons per day, during the peak of the summer. Mature trees have so much more leaf area; they require at least twice the water to prosper, than does the same area of bluegrass grass lawn. This means that the lawn sprinkler system that you installed is probably NOT taking adequate care of your trees. While some of this is specie specific, the fact remains that adequate water is required for your trees to capture solar energy and maintain themselves and grow.

People first settled in this area along the streams because there was water to sustain their life and the stream provided water to sustain the populous species that grow in our area and provide a respite from the sun and the wind. (It takes a BIG Big Sagebrush to provide much shade.) As we moved away from the streams into communities and onto developed farmsteads, we took trees with us to provide shade and shield us from the wind. When we did that we began to deny them the resource that they needed most to prosper, water.



People often think that trees extend their roots through the soil until they find water. This is an incorrect perception. Plant roots grow from the very smallest tips, and only grow through moist soil. People also often believe that a tree’s root system is the mirror image of its top growth which is also a misconception. Most trees have roots systems that are only 18-36 inches deep, and often spread out to 2 or 3 times the drip-line diameter of the tree. All the active roots are at or beyond the drip-line, so watering at the base of the tree is a waste of time!


Drip-Line Diameter     Water Use Per Day (gals)   Water Use Per Week(gals)
5                                              2.5                                         18
10                                            8.0                                         55
15                                            18                                         124
20                                            32                                          220

Reduce irrigation in beginning in mid-August to “harden” trees for the winter. After tree growth stops in the fall, deep water your trees, especially evergreens to sustain them through the winter.

For additional information, contact your Extension Office at 527-8587