Tree Irrigation Basics

Lena Davenport, ISA Certified Arborist, #PN-6217A

Proper watering practices are vital to the survival of a newly planted tree. The most common cause of decline in newly planted trees is improper irrigation. Improper irrigation can be either too much water or too little water, and the symptoms of stress from both can be indistinguishable. Proper irrigation requires a little investigation, continued monitoring and adjustments when necessary.

Irrigation amount and frequency are dependant on:

  • Season
  • Air Temperature
  • Soil Texture
  • Soil Structure &
  • Tree Species

With so many factors it is difficult to give an irrigation standard that is appropriate for all trees and landscapes. Generally, no irrigation is needed when trees are dormant. The period of dormancy for deciduous trees is easy to determine because they lose their leaves. Evergreens go dormant also. Use deciduous trees as indicators for the dormancy period for both types of trees. Irrigation should begin when deciduous trees start to bud up or leaf out in early spring. The most amount of water will be required mid to late summer when soil moisture has been reduced and air temperatures are at their highest. In mid to late fall the irrigation schedule can be tapered off back to a watering schedule that was used in early spring. Once fall leaf drop occurs discontinue watering until the next growing season.

Big Trees, Inc recommends that trees be irrigated with automated drip irrigation. This type of system can be as simple as a soaker hose attached to a battery operated watering timer. Drip irrigation uses the least amount of water with the highest efficiency. It evenly distributes water directly over the rootball of newly installed trees and it provides consistent moisture levels.

It is best to water deeply rather than frequently. Letting the soil partially dry (but not completely dry) between cycles promotes better soil structure and better rooting. The feeder roots (fine hair like roots) of trees typically grow in the upper 12” of soil where both oxygen and moisture are available. This is the area that will need to be wetted each irrigation cycle.

Clay soils retain moisture and nutrients much better than sandy soils, but clay soils accept moisture much more slowly. Sandy soils accept water freely but water drains from the soil much more quickly. Generally sandy soils will require shorter more frequent irrigation periods where clay soils will require longer infrequent irrigation periods. To find out what type of soil you have click here.

So how do you know if you have achieved the right irrigation frequency and timing? One simple method that gives good results requires some investigation:

  • Use a trowel to dig down at the root zone approximately 4-6”. Pick up a small handful of soil and squeeze it tightly in the palm of your hand. If the soil has formed slightly to the shape of your palm after you have opened your fist, the soil moisture is ideal. If the soil easily crumbles and falls apart the moisture level is too low, and if you are able to squeeze water from the soil when it is in your fist the soil is too wet. All water should be absorbed within 6 hours, and no puddling should occur in the root zone.

Trees absorb both oxygen and water from the soil. Overly saturated soils have little available oxygen and soils that are too dry hold any moisture so tightly that it is unavailable to trees. It is a fine balance that requires continued monitoring and adjustments.

Placing a layer of mulch over the tree root zone has many benefits. Organic type mulches help to maintain soil moisture by reducing water evaporation, allowing you to use less water. Organic mulches also moderate the soil temperature, reduce weed growth, slow soil erosion, and can lessen soil compaction. In the long run mulch improves soil structure, improves plant health and encourages growth. A two to four inch layer of mulch is ideal.   When placing mulch be sure that it is pulled back at least six inches from the base of the tree. Placing the mulch right up to the base of the tree can cause decay in the trunk and will result in health problems and even tree death.

If you have any questions regarding the irrigation of your newly planted trees from Big Trees, Inc. please do not hesitate to contact us.

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