By John Thompson
Member, Corrales Tree Committee and N.M. Tree Steward
Keep your trees alive during the drought! All of New Mexico is in a drought and Sandoval County is in an extreme to exceptional drought condition. Keeping the trees alive in your landscape should be your first priority for watering during the drought. Trees are the most valuable plants in your landscape and add up to 10 percent of the value of your property, plus they provide cooling, wind reduction, shade and many other environmental benefits. Trees take the longest to replace if killed during a drought. With little rain, your trees are not getting enough moisture to their roots even if you are continuing to water lawns and landscape plants near those trees. The higher temperatures, wind and low humidity during a drought cause trees and shrubs to lose water faster through transpiration. An extended period of drought such as we are currently experiencing causes stress on trees that can kill or weaken them. Trees stressed by drought are more susceptible to pathogens such as fungi and insects. Remember the devastation to piñon trees caused by the pine bark beetle in our last drought.
What do I need to know about watering during a drought?
• What is my soil? How you water depends on what kind of soil you have. In Corrales, there are two predominant kinds of soil. In the foothills the soil is likely to be sandy which means watering needs to be shorter but more frequent. In the greenbelt, soil will have a large amount of clay that holds water requiring longer watering at longer intervals. Loamy soil will hold water better sand and less than clay.
• What trees do I have? Different trees have different water requirements. You can find out if your trees have low, medium, or high water usage by checking with the NMSU plant database at https://aces.nmsu.edu/pes/lowwaterplants/index.html or the New Mexico Plant Database at http://wuc.ose.state. nm.us/Plants/home.jsp
• Where do I water my trees? Too many people mistakenly water only at the trunk of a tree. Water is best applied to the feeder roots of the tree that are predominantly under the canopy of the tree but can reach out well beyond the canopy. The best place to water is at the drip line at the outer edge of the canopy.
• How much do I water my trees? The amount of water needed every month varies by the season, and size and type of tree. The amount of water needed at one watering is what is needed to provide moisture to root depth (1-3 feet). The best way to tell is to check for moisture at about 12 inches deep the day after watering. This can be done with a probe or digging a small hole. Mature producing fruit trees require the most water —up to 800 gallons per month. Low water usage trees can exist on 200 gallons per month. Mature landscape trees can require 400-600 gallons per month during the summer.
• How often do I water my trees? Frequency of watering varies by season and type of soil.
Sandy soil requires less water but more frequent watering. Clay soil retains more water for longer so requires less frequent watering. Newly planted trees and shrubs need the most frequent watering to encourage root growth. Frequency of watering for mature trees may vary from once a week to once a month depending on season and type of tree.
• What’s the best way to water my trees? Bubblers or emitters on drip systems are the recommended way to water landscape trees and shrubs. When you water lawns and flower gardens with sprinkler systems, you are only providing moisture to 4-12 inches deep; whereas, trees and shrubs need moisture to 24-36 inches deep. Emitters or bubblers should be placed in the active root zone just outside the outside edge of the canopy. Emitters are rated in gallons per hour so that you can calculate how long to water for a given volume of water. Hand watering is also good. A tree well placed at the drip line (outside edge of canopy) will keep the water above the root zone until it is absorbed into the soil. As a rule of thumb, one inch of water in a tree well that is 10 feet in radius will provide about 200 gallons of water. Wood mulch 2-4 inches deep in the tree well will help retain moisture.
• What if I have conifers? Some conifers (e.g. Afghan Pines) have low water requirements but still need watering at least once a month to sustain their health. Conifers can be more adaptable to drought conditions once their root systems are established (2-3 years).
• What if I have fruit trees? Mature fruit trees require minimum amounts of water to produce fruit. In drought conditions, irrigation water may be restricted to once every three weeks. In cases of inadequate irrigation frequency, you may want to consider supplementing irrigation with hand watering or a water truck for larger fields. To retain moisture, trees should be mulched with wood mulch to a depth of 2-4 inches under the canopy.
• What if it rains? If you receive more than .5 inch of rain you can skip one watering day.
• What are the signs of drought stress? Conifers will show drought stress in thinning, browning, yellowing, or graying of needles. In the second year of a drought, conifers will produce excess cones. Deciduous trees will show stress through scorched leaves, yellowing of leaves, leaves dropping early, thinning of canopy, and twigs or branches turning brittle or dying.
• What is the minimum amount of water required for survival in a drought? Trees may not recover if deprived of water for too long a period. Once a month is a rule of thumb for minimum watering frequency for survival during a drought.
• What if I need more information? These are resources that provided information for this article and can be accessed online.
• Sandoval Extension Master Gardeners: http://sandovalmastergardeners.org/
• Gardening with the Masters Online classes http://sandovalmastergardeners.org/gardeningclasses/gardening-with-the-masters-online/
• NMSU Desert Blooms website: https://desertblooms.nmsu.edu
• Albuquerque Bernalillo County Water Authority: http://www.505outside.com
• New Mexico Office of the State Engineer U.S. Drought Monitor. www. drought.gov/states/new-mexico#current-conditions
• New Mexico’s Enchanted Xeriscape Guide.