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Gardening: Image

A wide variety of low volume irrigation (LVI) systems are available for the homeowner. The Galveston County Master Gardeners will sponsor a seminar on LVI systems for the home gardener on Saturday, August 18, 2007.

Photo Credit: William M. Johnson

Itís Dry! Seminar on home irrigation system is now appropriate!

By Dr. William M. Johnson, Galveston County Extension Agent - Horticulture

August 15, 2007

The Dog Days of August are howling! The heat is on and the frequent rains are a memoryóat least for now.

I had the pleasure of not having to discuss the need to make sure newly transplanted trees and shrubs were mulched, that container plants would need daily watering, etc. That was then and this is now.

The only positive thing about the onset of hot dry weather is that it makes it easier to promote the advantages of establishing an efficient irrigation system to service the home landscape and garden. Yes, it takes audacity to promote an educational program on irrigation when there has been water, water everywhere up until lately.

Letís face itóAugust tends to be a rather dry month and homeowners who install an efficient irrigation system now will have it whenever itís needed.

But first, the basics on the upcoming program. The seminar is entitled ďA Homeowner's Guide for Low Volume Irrigation (LVI) SystemsĒ and will be conducted on Saturday, August 18, 2007, from 9:00 - 10:30 a.m. at the Galveston County Extension Office in Dickinson . There is no registration fee but seating is limited and reservations are required (281-534-3413, Ext. 12 or

This seminar will be conducted by Louis Mickler, a Harris County Master Gardener. Louis has gained a wealth of knowledge and experience regarding low volume irrigation. He is coordinator for the Master Gardener Class, Green Thumb Gardening Series and The Ask the Master Gardener Kiosk for the Harris County Master Gardeners Association at Precinct Two.

Topics to be addressed include: advantages of low volume irrigation systems, how to design a system, components of a system and how to install a low volume irrigation system. Hands-on demonstrations will be conducted.

Now, what exactly is a low volume irrigation system? Low volume irrigation systems come in many different forms but can be described as the practice of applying water where itís needed and when itís needed with minimal loss to evaporation or to runoff into storm sewers, drainage ditches or waterways. A low volume irrigation system distributes a measured amount of water over a specific period of time using a system of delivery and distribution pipes and application emitters. Low volume irrigation systems are designed to maintain an evenly moist root zone.

Gardenerís Q&As

Q: Why do you recommend that pruning paint not be used on trees? I have always believed that applying pruning paint is a good procedure.

A: It does seem counter to common sense to leave a wound uncovered when we consider it from a human perspective. That is the way we tend to think about wounds, but remember a tree is not a human, or even an animal, and responds to things in a different manner. In the natural forest, branches break from trees from wind storms, heavy rains, etc. Trees must have a mechanism to defend themselves without a gardener going into the forest and applying wound sealer to every injury. Certainly, some of these breaks can cause problems for the tree, but in most cases the tree has the natural defense mechanisms to manage the problem.

A tree doesn't "heal." It only closes over the wound, enclosing the damage inside the tree. It has the ability to compartmentalize diseased and damaged tissue, thereby sealing them from the healthy tissues in most instances. These damaged areas then remain in the tree and can be seen many years later if the tree is cut. It is possible to see scars (compartmentalized damage) caused by fires 50 and 100 years before the tree was finally cut. There are instances when the damage to a tree is too severe and the tree rots internally, but such damage cannot be stopped by a pruning sealer.

Some people think that a pruning paint will help prevent the tree from "bleeding to death." Trees don't bleed as they don't have blood. The blood in an animal is critical because it carries oxygen to all the cells within the body. Plant sap carries water, minerals and sugars, but does not carry oxygen. Loss of blood in an animal will cause cell death for lack of oxygen. Plants don't have this problem. They can lose a lot of sap without major injury. The dripping sap just irrigates the tree. Pruning paints will have little effect in reducing the dripping of sap. It just stops naturally as the tree compartmentalizes the wound.

Many pruning paint compounds are black and contain asphalt. This black material absorbs our intense Texas sunlight and can become quite hot if exposed to direct sunlight. The heat can damage or even kill the tender cells that the tree produces to close the pruning wound and in that manner delays wound closure and compartmentalization. Lighter-colored materials do less damage, but any containing a petroleum-based solvent can damage newly developing wound closure cells.

Scientific research has shown that the application of a pruning paint is not necessary. Much more important is proper pruning technique. Knowledge of tree anatomy and physiology allows us to prune a tree and allow the tree to use its protective mechanisms to protect itself. It is also wise to minimize pruning in landscape trees by training a tree when it is young. Cutting small branches when the tree is young precludes the necessity to cut larger branches later. The large wounds produced by removing large branches create greater difficulties for the tree.

Dr. Johnson is a horticulturist with the Galveston County Extension Office of Texas Cooperative Extension, Texas A&M University. Visit his web site at

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