Watering: Know when to say when

Tue, 07/31/2007 - 1:12pm
By: The Citizen

By Brian Arnold

Recently, while digging, almost paddling, through the saturated soil in which a poorly performing specimen tree was planted, I listened to the concerned home owner explain that she has diligently watered the tree as much as she can, within the current water restrictions. She went on to explain that because of the frequency of watering, the decline of the tree “can't be from a lack of water”.

Even before I found the first rotted root, I knew that she was right. For, as it is with my well meaning and watchful homeowner, so it is with many others.

“You really need to reduce the frequency of your irrigations,” rolled off my tongue as if I'd said it countless times before. Reason being, I had.

Countless times I've explained how critical it is that adequate oxygen levels be present within the root/soil environment, and that too frequent watering may lead to an anaerobic condition, which is destructive to living plant tissue. This is because roots, which carry on respiration, have insufficient oxygen to do so in a water-logged environment. I went on to explain that, as if the above isn't bad enough, a root/soil environment that is frequently wet, often allows “root rot,” causing disease organisms, which kill plants.

At this point, I often must reach for the little bit of psychological knowledge that I have and try to help my homeowner pass through phases of disbelief, frustration, and denial. I try to comfort them by informing them that they are far from being alone in making this mistake. I tell them of how Dr. Jean Williams-Woodward, the Plant Pathologist responsible for the operation of the Plant Disease Clinic at the University of Georgia, has frequently commented that when watering restrictions are enacted, the bulk of plant samples received at the clinic are those that suffer from over-watering. Presumably, because of the numerous landscape owners feeling compelled to water on “their days.”

As a “plant person,” it's difficult to give a “one size fits all” recommendation in regards to watering needs. However, it is generally held that established trees, shrubs, and groundcovers favor a good ground soaking watering event, once per week. Any more frequently and the risk of root rot as well as other diseases, becomes increasingly likely.

Un-established trees, shrubs, and groundcovers, though seemingly over-watered by many landscape owners, often require water more frequently than once per week. While this is no surprise, I venture to say that I encounter at least as many over-watered plants as I do under-watered plants within relatively young landscapes.

Depending upon the degree of establishment, the species plant involved, the soil in which respective plant is growing in, its exposure to sunlight, and other factors, a plant within a given landscape may not suffer from lack of water, for several weeks. Another plant, within the same landscape, may suffer from lack of water much sooner.

With the above in mind, awareness of distinct environments within your landscape, as well as of the needs of various plants within those environments, becomes worthy of the effort.
To provide any sort of justice to the true dynamics of proper watering of turf, detail beyond the capacity of this writing must be considered.

In the most simplest terms, an established lawn growing upon good soil and benefiting from proper mowing and other maintenance practices, will need water less frequently than a lawn with less favorable conditions.

Having stated the above, it is generally held that lawns favor a watering event that results in the equivalent of one inch of rain per week.
Like trees, shrubs, and groundcovers, managing water so as to prevent the soil of established lawns from being constantly wet, is critical. If possible to water once per week without moisture stress occurring, certainly do so.

However, many lawns will need water more frequently, in order to perform best.
Un-established sod lawns, having all roots virtually above the soil upon which laid and therefore in an air laden environment, need moisture to be re-supplied rather frequently until establishment occurs.

If you have an irrigation system without a working rain sensor, the decision of installing one is a no-brainer and will aid in preventing the dilemmas above. They are, considered by most, to be very affordable and actually “pay for themselves” quickly, when savings on water usage is considered.

In addition to being cost effective and beneficial to your landscape, using a rain sensor on your irrigation system is an environmentally responsible thing to do, as water isn't wasted upon a landscape that just received adequate rain.

By understanding the basics regarding landscape water, you can avoid the psychological ramifications experienced by my friendly homeowner, mentioned above. In so doing, keep in mind that while improper watering may not always manifest in dead plants, it is likely that some plants are not performing nearly as well as they could be.

Brian Arnold holds a bachelor of science degree in ornamental horticulture from the University of Georgia. He is manager of the Tree, Shrub and Turf Care division of Nature’s Landscape Services and president and owner of Brian Arnold & Company, Inc., a tree, shrub and turf care company.

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