“Water is the most limiting factor for tree survival and growth” according to Texas Agrilife. Although there is no magical formula or exact rule for when to water and how much water to provide, there are general guidelines that can help home owners protect their landscape trees.
Do my trees need supplemental water?
How much supplemental water a tree needs depends on the time of year, type and age of the tree and soil composition. Clay soils, while taking longer to wet, will retain moisture longer. Sandy soils, which easily absorb water, dry faster. (Texas Forest Service, “How do I care for my tree”). The heat of Texas’ summers can dry out soil quickly and long periods of drought are extremely taxing on a tree’s resources.
To quickly check if the soil surrounding your tree is too dry, you can do what is called, “the screwdriver test”. Using a long screw driver, try to push it into the ground. If the ground is dry, you won’t be able to. If the ground is moist, you will. If you can’t get your screwdriver to easily sink at least 6 to 8 inches into the ground, it’s time to water. (Texas Forest Service: Tree watering tips)
Quick guidelines on watering trees:
- During drought, mature trees need to be watered about once a week, while younger, newly-planted trees need to be watered about three times a week.
- For mature trees, add a minimum of 1 inch of water per week (if no rain).
- In a normal North Texas winter, for mature trees, there is sufficient rain for the trees to remain healthy. But if it is abnormally dry, water about once a month.
- If you want to do a water audit, put out some flat-bottomed cans, such as tuna cans. Run the irrigation system (or sprinkler). See how long it takes to get 1”.
- Infrequent, slow, soaking watering is more beneficial than frequent, shallow watering. Shallow watering encourages shallow root development.
- If on a slope, you may have to water for a few minutes, then stop, then start again to prevent runoff.
- Overwatering is also harmful. When all the voids between soil particles are filled with water, no oxygen is present to be exchanged (anaerobic). The tree (or any other plant that lives in soil) will die.
The best way to add water to your tree’s root system
There are various ways to add water – irrigation systems, hand watering, sprinklers, soaker hoses, and other devices. The best way to water trees is gradually with a soaker hose or by trickle or drip irrigation. Overhead sprinklers are less efficient but can be used. If using overhead sprinklers, water in the early morning to reduce evaporation.
Water beneath the crown and a few feet beyond the dripline. Watering close to the trunk is not really necessary for a mature tree; the roots extend about twice the height of the tree (or more). The majority of the feeder roots are away from the trunk.
If using a soaker hose, wrap the hose around the tree’s base several times beginning with the end of the hose roughly 18 inches from the trunk and wrapping outward about 18 inches apart until the area covered includes all the tree’s canopy plus a few more feet. The soaker hose may be placed above or below mulch. Soaker hoses may have uneven pressure or develop leaks that limit an even distribution of water. It is important to check the soil moisture in several locations around the tree when using the soaker hose watering technique.
If choosing a drip system to water your trees, it is necessary to calculate the best spacing for emitters based on soil texture and the length of the tubing to cover the area to be watered. The University of Utah recommends the following emitter spacing and provides the following recommendation for calculating emitter placement:
“Soil texture determines how much area is wetted by each emitter. To calculate the number of emitters needed for each plant multiply the area to be wet by the percentage to be covered, divided by the area wetted by each emitter. For example: Given a 15-foot crown diameter tree (176.71 square feet of coverage) growing on loam soil (21 square feet of distribution per emitter) with a desired 60% coverage of the root area, you need 5 emitters.”
If you choose overhead sprinklers to water your trees, place a rain gauge or can, such as a cat food or tuna can, placed in several locations around the tree to determine how long to water until the gauge or can show 1-inch accumulation.
Caution: “Do not fertilize a tree that is under drought stress.” The salts in chemical fertilizers may burn roots when there is not sufficient water. Fertilizers may also stimulate top growth resulting in too much leaf area on the plant for the root system to maintain during periods of limited soil moisture.” (Tree Watering Necessary During Drought Conditions University of Colorado Extension Service)
Clatterbuck, W., “Watering Trees,” Agrilife Extension Publication. Retrieved from http://water.tamu.edu/files/2013/04/how-much-to-water-trees.pdf
Texas A&M AgriLife: “How much to water trees”. http://water.tamu.edu/files/2013/04/how-much-to-water-trees.pdf