Hannah Mills, Laramie County Horticulture Program coordinator (University of Wyoming Extension), has been on at least 50 yard calls this growing season.
A yard call is a request for Hannah to come see a plant problem. Smaller problems, like infected leaves, can be sealed in a sandwich bag and dropped off at the office, fourth floor of the Pathfinder Building at Laramie County Community College, or photos can be emailed to hmorneau@uwyo.edu.
The most frequent yard call, half of the four calls she made on a recent Wednesday is, Hannah said, “‘My trees are not doing well.’ I’m seeing established pine and spruce trees and they are dying. People want to know how to fix the tree. I ask them, ‘How much water do they get?’”
Spruce and pine trees are not native to Cheyenne and the High Plains, Hannah reminded me. They need more water than what naturally occurs here. They grow in the foothills and mountains, where there is more precipitation. They also grow on the shady north-facing slopes, and they grow in groups, giving each other more protection from drying wind than if they stand by themselves.
Then there’s Cheyenne’s variable weather. This year, for instance, January through May had hardly any rain or snow, and little snow cover to protect moisture in the soil. Winter wind dries out the needles, and a spruce or pine tries to get moisture from the soil, but the wind, the lack of rain and snow, and lack of snow cover protection, has dried it out. Our summer deluge was too late, especially for stressed spruce.
Stressed trees can’t fight off ips beetles (spruce) and pine beetles because they don’t have the moisture to make the sticky pitch to entomb the invaders. Successfully fighting off other ailments requires good hydration, too.
We like living with trees. We like looking at them. They protect us from wind and too much sun and lower the temperature a few degrees in the summer.
So, how do we keep trees alive in Cheyenne, especially spruce and pine? We water them.
How much water do trees need?
The Wyoming State Forestry Division recommends in the summer that trees receive 10 gallons of water per inch of trunk diameter per week.
My two 60-year-old silver maples are each 36 inches in diameter (not circumference), at breast height (4 feet above ground level). So that’s 360 gallons each a week. Less if it rains.
Where do you put this water? Under the branches, within the dripline. This is the circle on the ground beneath the tips of the branches that stretch the farthest out. Some roots might stretch beyond.
You want nice deep watering: 80% of the roots taking up water are within 18 inches of the surface.
How can I measure 360 gallons of water? For a hose, mark a spot on the handle (I used a twist tie on the edge of mine) and use that marker to calculate how far you usually turn the handle—90 degrees, 360 degrees, etc. Then time how long it takes to fill a 5-gallon bucket. Use your phone’s clock app’s timer. If it takes 50 seconds to fill the bucket, then it will take only 10 seconds for a gallon, and 3600 seconds for 360 gallons, or 60 minutes to water the tree with the hose or hose with sprinkler.
If you have sandy soil, an hour won’t be a problem, but if you have clay soil, tough for water to move through, you might want to break watering into two shorter sessions or water at a slower rate to avoid water running off and down the street and sidewalk.
Foresters talk about “green death,” when trees planted in lawns can’t compete with the turf for water. The cure is to water longer, but less often so the water goes below the turf roots. After watering, use a screwdriver to see how deep the water went — the tool should easily pass through moist dirt and be stopped by dry dirt.
Winter watering
Water trees in winter. State Forestry says do it when it’s over 40 degrees or at least once a month. Hannah suggested watering in the morning, as far in time from the evening drop below freezing as you can.
Tough tree species
Hannah suggested that junipers need less water than spruce and pine.
She said ponderosa and Austrian pine like our alkaline soils, so they are a good choice, if you are willing to water them enough.
In the deciduous category, Hannah recommended burr oak, native to northeastern Wyoming. It needs less water than other leafy trees — especially cottonwoods — which normally grow along creeks and rivers.
Beware healthy trees that aren’t purposefully getting watered — they’ve probably tapped into your sewer pipe.
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