Proper Watering Techniques

By Don Williams, the Tree Wizard

Most people do not water their trees properly. The belief that a tree living 100 years or more does not need proper watering and fertilization leads to the loss of some very large, valuable trees. It is obvious that a young, vigorous tree does not need as much water and food as an older, mature tree. The mature tree, however, is only receiving the quantity of nutrients and water it did when young. The larger the tree, the more water and fertilizer it needs.

To give insight on this, I will first say that a tree’s roots begin at the trunk and extend close to the drip line or beyond. Healthy tree roots can extend to twice the size of the canopy. In trees that have been stressed or dying back for years, the active feeder roots die from the outer tips and recede toward the trunk to maybe half the distance from trunk to drip line.

This explains why only watering or fertilizing at the drip line on a stressed or dying tree will usually not be successful. It is the entire root zone containing the feeder roots that determines the long-term health of a tree.

We do not recommend watering with an open-end water hose at the trunk as this can cause rot at the base. The object of watering is to keep the entire root zone in a moist condition never allowing the roots to completely dry out in hot, dry summers.

Lawn watering sprinklers only water shallowly and are not designed to water the deeper roots of trees. An ideal but not often used approach would be to install a separate watering system specifically for the trees.

This would water all the roots and remain on long enough to deeply penetrate the root zone. In 35 years, I have only seen one person install this type system. In reality, we must approach tree watering differently. During hot, dry Texas summers, trees need deep watering of their entire root system – trunk to drip line - every ten to fourteen days.

For deeper water penetration, it takes about three hours to water each tree. The watering time can be shortened if water begins to stand due to situational differences within a yard, such as drainage. Short of installing a separate system, the most successful method for watering trees is to use a simple, non-mechanical, circular sprinkler attached to the end of a hose. Place it under the tree or close group of trees and turn the flow on enough to cover the entire root zone.

On much larger trees, you may need to move the sprinkler around the tree and water each location for about three hours. The use of watering injection rods is highly laborious and mostly ineffective because you’re not reaching the full root zone and may be reaching beneath the roots. Cracks in the sub-rock area may allow water to disappear through the cracks therefore, it is best to water thoroughly from the surface and allow it to flow through to the roots. This watering schedule should be followed during the four to five months of hot, dry weather.

In cooler months, the watering should be done maybe once a month unless it produces standing water. During rainy months when we receive rainfall in excess of two inches, you can skip the next scheduled watering. It is common sense that during rainy months with successive rains you can skip watering your trees altogether.

Usually the months of May through sometime in October the approximate two-week watering schedule is essential for your trees’ continued health. In cooler weather with no rain, you should still water every four weeks using the preferred method.