Water requirements for trees are substantial, particularly for large trees. For example, a full-grown pecan tree can use nearly 200 gallons of water on a hot, summer day. Over the course of a year, that same pecan tree will use between 3,000 and 6,000 gallons of water.
The majority, 90%, of this water is lost through the process of transpiration. This evaporation of water from the leaves allows water molecules with attached essential nutrients need for growth to move from the absorbing roots through the trunk and into the branches. Without water, trees are unable to transport nutrients and complete their photosynthetic processes.
Replacing this level of water is difficult, costly and unsustainable from a water resource perspective. The good news is that it is often unnecessary for most mature and well-established trees. Established trees, with healthy root systems undamaged by recent building construction, will have an expansive root system capable of suppling some of this water. As a result, only supplemental watering is needed to help trees through periodic droughts. The following guidelines can help with watering established trees.
• Identify stressed species first: Look for evidence of drought stress (wilting, yellow foliage, leaf drop, etc.). For large, mature trees with undisturbed root systems, water only if signs of drought are evident.
• Check soil moisture: The easiest test is to dig a 6- to 9-inch hole. If the soil is cool and moist, you don’t need to water. If the soil is dry, it is time to water.
• Water the tree’s entire growing area: Roots extend two to three times the tree’s dripline. This makes watering the entire root system difficult. Instead, focus on watering the entire area under the tree’s dripline and a bit beyond, if possible. Covering more area is better. Avoid watering the tree’s trunk or foliage. This can promote disease and insect outbreaks.
• Water deeply: It is important to ensure water penetrates deep into the soil. For mature trees, deep periodic watering is preferable to frequent shallow irrigation. Frequent shallow irrigation promotes shallow rooting and increasingly less drought-tolerant trees.
• Water quantity: Start by applying 1 inch of water once per week. If using a sprinkler, place several small containers in the watering area to measure when you have reached one inch. Measure the time it took to fill those containers to help ensure accurate watering in the future. Finally, wait two hours, then dig a 6-inch hole to check and ensure water percolation and deep watering. If the soil is still dry, apply another half-inch.
• Watering frequency: A simple recommendation is to water once per week. However, watering frequency will be dependent on soil type, soil compaction and slope. For example, sandy soils might be watered only a half-inch two times per week. Clay or compacted soils might need longer duration. Be sure you are getting good percolation.
Timing: It is best to water trees in the early morning hours. This avoids water loss to evaporation during hot summer days. Evening watering runs the risk of promoting fungal diseases by keeping landscapes wet overnight.
Recently planted (within the last year) or unestablished trees should be watered frequently. Establishment times vary around the country from between 3 to 6 months per caliper inch in diameter. Caliper inch is measured 6 inches above the ground. To ensure survival, water newly planted trees two times a week during the establishment period. For vigorous growth, water trees daily for the first month and two to three times per week for the remainder of the establishment period. Be sure to water trees slowly to prevent runoff and ensure a deep soaking. Using products like Gatorbags, which can be quickly filled and slowly release water, can make watering easier.
Upcoming Extension Programs
• Etowah/Cherokee County Master Gardener Class: Begins on Jan. 28; contact the Extension Office for more details or an application
• Enroll young people ages 9-18 in the 4-H program at www.alabama4h.com.
For more information on this topic and many others, contact the Etowah County Extension Office, 256-547-7936 or 3200 A W. Meighan Blvd., Gadsden. Amy Burgess is extension coordinator for the Etowah County Extension Office.