Deb Babcock: Keeping trees healthy during a drought
July 16, 2012
With water restrictions in place throughout Routt County because of the drought this year, many gardeners are wondering how their trees will fare without much rainfall. It's tough to keep our trees healthy in the Yampa Valley even in wet years, so what should we do to protect our investment in trees during a drought?
For one, if you have to choose between watering your lawn and adequately watering your trees, opt for the trees. A damaged lawn can be restored in a matter of months, but large trees will take 20 years or more to be replaced. And as I wrote a few weeks back, lawns will simply go dormant when they don't get enough water to stay green, so chances are you won't hurt the grass by withholding water.
You'll be able to tell if your trees are getting stressed from lack of water. On deciduous trees, the leaves will look wilted or even start curling or drying out and turning yellow or brown. Evergreen needles will start turning brown, yellow or purple and dropping off the trees more than normal.
Wind and heat are particularly hard on trees and shrubs because the moisture that comes from rain or from watering evaporates quickly. This is especially true for trees with south or west exposures that receive more hours of our most intense sun here in the mountains.
If your garden soil hasn't been improved with compost or other organic materials, it probably doesn't hold water as well as amended soil. Any water your garden gets will be held in like a sponge if you have organic materials mixed into your soil. If it's primarily sandy, clay or rocky with lots of shale, the water tends to just run off or go through the soil where it cannot be used by your plants.
If you mulch around your trees — out from the trunk about six inches so small animals don't borrow down and make a nest there — you help the soil retain moisture. To prevent evaporation from wind and heat and our dry climate, add one to two inches of mulch. This also will help keep down weeds which will steal water from the soil and the roots of your trees.
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So what is the smartest way to water your trees during the drought?
■ Water in the very early morning or late at night to prevent evaporation during the hottest and windiest times of the day
■ Water slowly so that the moisture will seep deep into the ground — a depth of 12 inches is best for established trees. A soil needle or deep-root feeder attached to your hose is a great way to get water efficiently down to this level. Avoid digging holes in the ground to get the water down there as you'll only end up drying out the roots. Overhead spraying of the leaves is simply wasteful and inefficient and doesn't help the tree where it really needs the water: in the soil at its roots.
■ Water the soil within the drip line (where rain water drips off the outermost leaves of deciduous trees). For your pines and spruces, go three to five feet beyond the drip line because these trees spread their roots shallow but far from the trunk.
■ A general rule of thumb is to give your tree 10 gallons of water per inch of trunk diameter at the height of your knees. Most hoses produce about 10 gallons of water in five minutes. So a tree that is six inches in diameter, will receive adequate water in 30 minutes.
■ CSU recommends watering trees three times per month from April to September.
■ The best practices for tree watering include: soaker hoses coiled around the tree within the drip line area, five-gallon buckets with small holes punctured in the bottom placed around the tree in the drip line area, deep-root feeders attached to your hose, or a shower attachment to your hose aimed at the area within the drip line.
Often drought won't be the cause of death in a tree, but the stress from lack of water can weaken the tree and make it more susceptible to disease or insect infestations that it won't be able to fight off.
Deb Babcock is a master gardener through the CSU Extension Routt County. Call 970-879-0825 with questions.