We are getting close to the time hard decisions about watering trees will begin. If you haven’t already, you may want to prioritize which trees to water. Be sure to identify the trees that are most valuable and need protecting.
Keep in mind, crowded trees compete for space, water, sunlight, and nutrients. If you have too many trees, you may have to decide which are most valuable and which can go. There was a long list of other tree considerations in last week’s article.
What trees need water? The thirstiest tree species will begin to show signs of stress and decline the fastest. Some high water use species may be up for...removal! Weeping and globe willows, cottonwoods, sycamores, pear, pecan, and many ash species are high water users. They are the ones that generally end up with brown leaves and early defoliation following hot, dry summers. On the other spectrum, desert willow, cedar elm, lace bark elm, mesquite, Texas mountain laurel, are lower water users. If they are established they may only need one good watering a month. During the very hottest, stressful months, like June, July and August, they may need to irrigations a month. There are more good tree species we can take advantage of that are better adapted to life in West Texas.
Water in the top 12-18 inches of soil. The majority of tree roots are located in the top 12-18 inches of soil. One to two inches of water should wet the soil to the depth of the root zone...depending on soil texture. Sandy soils don’t hold as much water as clay soils so if you over water a sandy soil, water moves down past the root zone. Clay soils can hold 2-3 times as much moisture as a sandy soil, so they don’t need to be watered as often as a sandy soil.
Use a long screwdriver or soil probe to see how deep the moisture goes. This is a good way to determine if soil moisture is deep enough to sustain a tree. Just push the screwdriver blade into the soil and where it stops is where dry soil begins. Try several areas to rule out rocks and roots and to check for even watering.
Water at the drip line of the tree. Tree roots that take up water and nutrients are located at the dripline of the tree (area below where branch tips end). Don’t apply water at the base of a mature tree, put it at the dripline. For a large tree, water several feet inside and outside the dripline.
Consider irrigation driplines or soaker hoses. Two to three loops of these can be laid in the dripline of trees and connected to a water hose to distribute water. If you make your own dripline which is very easy, choose emitters that release at least 1 gallons of water per hour. Drip and soaker hoses will need the volume low enough that water doesn’t spray into the air.
Mulch, mulch, mulch. Mulch trees out to the dripline with 4" of mulch. This will suppress grass growth, slow evaporation, conserve soil moisture and keep soil temperatures cooler in the summer months. Look for bulk mulch providers like tree pruners, municipal mulch, recycle centers often have mulch.
Trench in towards the tree trunk, not across the roots. If you have to do any trenching for whatever reason, trench toward the tree trunk to limit the number of cut roots. If that’s not a possibility have an air jet tool dig the trench rather than a traditional root cutting trencher. An air jet doesn’t cut the roots but removes the dirt so pipes can be installed with harming the roots.
Next week we will discuss amounts of water.