Turf vs. trees: the competition for water

How to manage the biological irrigation contest on your course


Filed to: Trees, Water

tree roots
Tree and turf roots usually are “out of sight, out of mind,” but especially with trees, that’s not always the case. Photos by John Fech

Trees intermingled with or adjacent to turf share the same root zone. Thus, what you do to one, you do to the other, at least to a large extent. The results of that run the gamut from beneficial to detrimental and just OK.

f the tree is a low-water user and is next to a regularly irrigated green, tee or fairway, then that might explain why the tree is struggling, or worse yet, why the tree is being set up to fall over from rotten roots. Other trees are water tolerant, or even water loving, and quite compatible.

For the valuable trees on your golf course (likely most of them), a good inspection and consideration of how much water they receive is in order.

illustration of tree roots
Although there is variance by species, most tree roots are located in the upper 18 to 24 inches of the soil profile. Tree roots graphic courtesy of the Morton Arboretum

Roots are hidden

One of the biggest difficulties with this topic is that tree roots are hidden, at least from the downward view, looking at the turf plants and soil. It certainly would be easier if the subject at hand were, say, chinch bugs that feed on leaf blades. Not only are roots hidden from view, but they’re also usually not foremost in the thoughts of superintendents; as the saying goes, “out of sight, out of mind.

The saving grace of their location is the focus on turf roots, at least from a management standpoint, such as in the case of the turf diseases Pythium root dysfunction and summer patch.

illustration of tree roots
Tree roots are often not visible until the process of removing a tree begins.

So, where are the roots of a tree located? Of course, it can vary depending on the soil type and species of tree, but generally, the majority of a tree’s roots are in the upper 18 to 24 inches of the soil profile. Tree roots start at the trunk and generally grow horizontally to a width of two to three times the drip line of the canopy. Due to this root arrangement, golf course trees often take on the arrangement of a natural forest, with overlapping and intertwining of root systems.

With the location of tree roots in mind, when turf roots in the 1-to-12-inch range are watered, the unused portion of the applied water is absorbed by tree roots. This phenomenon occurs in natural settings as well, with trees becoming adapted to the average amount applied by Mother Nature. The concern is that tree roots that are growing in a turf area that is frequently watered to meet the needs of the turf may be keeping the tree roots (or root flare) moister than they should be.

illustration of tree roots
Tree roots and basal root flare are often adversely affected by overly frequent water applications.

Tree and turf competition

When growing in close proximity to tree roots, turf plants are often at a disadvantage. This sometimes results in turf thinning due to tree roots absorbing some of the water that would otherwise be available to the turf roots. When this occurs, it provides insight into where the tree roots are and where a conflict exists.

illustration of tree roots
Lack of adequate sunlight is a classic tree/turf conflict.

Another aspect of tree/turf competition is sunlight depravation. Trees are notorious for negatively impacting turf performance due to casting shade on a group of plants that usually grow best in full sunlight, especially turf species such as Kentucky bluegrass and bermudagrass. As described by J.B. Beard in “Turfgrass Root Basics,” turfs such as tall fescue and St. Augustine are often good choices in these locations due to their shade tolerance and their inherently deep root systems that are able to absorb greater quantities of moisture from the soil than shallower rooted species.

illustration of tree roots
Greater-than-optimal fertilization is another conflict when trees and turf are co-located.

In addition to competition for water, tree and turf roots also compete for nutrients. However, just like with need for water, trees often do not need supplemental fertilization, especially on “older” soils, ones that have not been disturbed recently and have had many years of leaf return and assimilation into the upper soil profile — ones with desirable soil organic matter content. As such, just like with the potential for excessive water to be applied to tree roots, the possibility of excessive amounts of various nutrients being added exists as well.

illustration of tree roots
Separation of turf and trees is influential in keeping the negative effects of excessive irrigation to a minimum.

Other conflicts

In areas where higher rates of nutrients are applied to turf, it’s wise to be on the lookout for symptoms of overfertilization on nearby trees. Generally, greater-than-optimal fertilization is visible as lighter or darker foliage, less or more than average stem growth and the presence of leaf feeding insects such as aphids, mealybugs and plant­hoppers. In these locations, tree leaves and stems should be added to the list of specifics to observe in a regular scouting routine, where turf insects and diseases are traditionally the focus of attention.

Another conflict between turf irrigation and trees can exist where tree trunks are located close to an irrigation head. Though this is usually only a problem where the head is closer than 20 feet or so, in addition to the spray pattern distortion, serious bark and cambial damage can result from frequent striking with a forceful water stream. A higher incidence of foliar diseases on small- to medium-sized trees can also occur where trees and turf occupy the same space.

Trees such as crabapple, hawthorn, pagoda dogwood, escarpment live oak, amur maple, redbud, ocotillo, persimmon and acacia can be defoliated due to frequent foliage wetting.

illustration of tree roots
Tree-only zones provide the advantage of being able to water plants according to their unique needs.

Separate trees and turf

Without supplemental irrigation, most golf course turf will experience serious stress, especially during periods of high evapotranspiration and daytime temperatures, having exceeded the permanent wilting point of various grass species. As such, in high maintenance areas — greens, tees, fairways — golf turf requires more irrigation than trees. The exception to the rule for trees is during periods of drought, usually typified by the lack of rainfall for 3-5 weeks in summer. When drought becomes influential, supplemental water will prevent permanent tree damage and lowered pest resistance.

illustration of tree roots
Removal and replacement of turf is an option in some situations.Photo by Emily Dobbs, University of Kentucky.

So, with all of these factors in mind, what can be done to overcome issues with too much or too little water applied to tree roots? Considering that the standard situation is that during the majority of a growing season, most trees — species that are native or adapted to the local natural rainfall patterns and soil makeup of the area — grow best without supplemental irrigation and fertilization, the most influential management technique is to separate trees from turf.

Creating a separation with the existing layout and architecture of a golf course may seem to be a drastic change. However, practical steps can be taken to improve the condition of the root zones for both entities. Several techniques can be utilized.

First, create high-, medium- and low-water zones on the golf course. This can be done in a variety of ways, but the most common is to examine the irrigation system map on each hole and draw in tree placement, noting areas of overlapping coverage and the likely spread of the roots of each tree. High-water zones commonly include greens, clubhouse turf and tees; medium-water zones include fairways and concession stands; while low-water zones include rough and out-of-bounds areas.

illustration of tree roots
Tracking shade patterns is a good method for identifying areas where removal and replacement of turf should be considered.

There are other zones to consider, such as a tree-only zones. In certain areas, where no golf turf is present, consider that the health of the tree resources may require separate tree watering systems, depending on how much water is applied to the turf or groundcover growing over the tree roots. In most cases, drip and microspray systems are best for this application.

Various other locations may not require functional turf, especially those that are not typically in play. Removal of turf in these areas may actually mean “replacement of turf,” converting these areas by installing other plant material or mulch. Pollinator and tall-, native-grass plantings would fit the bill in this category.

In other locations, tree removal might be a better option. Removal may be necessary where turf must be irrigated and fertilized at a high level, especially if symptoms of poor tree health are present. While this requires an outlay of financial resources, the ultimate goal is “right plant, right place,” and if a tree is receiving the improper inputs, then removal becomes a viable option.

Analyzing the amount of water, fertilizer and other inputs that are being applied by default to a given tree has additional benefits. When debating removal for other reasons such as potential liability due to decay, cracks and other tree defects, high costs of pest control, sunlight blockage and encroachment into a fairway, that analysis provides an additional factor for decision-makers to consider that might encourage them to act in the best interests of the golf course.

John C. Fech is a horticulturist and Extension educator with the University of Nebraska-Lincoln. He is a frequent and award-winning contributor to GCM.

Filed to: Trees, Water

You may also like: 10 functions of golf course trees