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Trees?EUR??,,????'?????< These are facts that nursery growers know well. Contractors who don?EUR??,,????'?????< A basic understanding of the structure of a tree?EUR??,,????'?????< How far beyond the drip line the roots spread horizontally, and where within this vast network of roots the most water is absorbed, are closely related. Generally speaking, tree roots will extend somewhere between one and one-half, to four times the diameter of the tree?EUR??,,????'?????< Heave ho! This olive tree (Olea europea) is headed to an uncertain future as it moves to a new home. Serious problems can develop when trees planted in turf areas are moved, because irrigated turf trains roots to spread near the surface. On the other hand, olive is a drought-hardy species that fares much better in summer heat than other trees. Photo by Guy Nelson Compaction Poses Problems A thorough understanding of compaction is critical to designing an irrigation system that meets the water needs of a maturing tree. Compounding this problem are the typical situations found in most urban plantings?EUR??,,????'?????< In an ideal situation, the irrigation designer will have input on the planting details for all installations. A sound irrigation design and proper planting will help ensure trees receive sufficient irrigation in order to develop healthy root systems. Well-developed root systems will thus produce healthier trees with fewer diseases and insect problems. Strong roots also provide anchors to prevent trees from blowing over in a strong wind. While creating a well-developed root system in urban settings is difficult to achieve, there are innovative ways to accomplish the objective. A more serious problem sometimes exists in a retrofit situation where an existing spray irrigation system (as used for turfgrass) is replaced with a low-volume irrigation system. Arborists have long debated the appropriateness of planting trees in turf areas. An intelligent irrigation designer will leave this age-old debate to the arborists, and determine whether the sprinklers for the turf will provide sufficient water. Trees planted in turf areas that receive water from overhead sprinklers are usually shallow rooted and compete with the turf for available water and nutrients. Most turfgrass roots are shallow, fibrous, and absorb water more quickly than the trees. This leaves trees with the table scraps, instead of the main course. To prevent this from happening, a separate irrigation system should be designed for the trees to provide the water to their deeper rootzones. Two bubblers and two drainage tubes are assigned to each date palm planted in July at a Southern California shopping center. Seen here after a cycle, this example of good installation shows no runoff to adjacent areas and limited pooling as the water soaks in via the 4-inch-diameter PVC drainage tubes. Dale Skidmore and Dave Lockridge (left) look over drip-system-grown trees at Shadetree Nursery. The cooperative venture produces drought-tolerant species tailored to Southern California. Most of these trees will need irrigation help during an establishment period but should do fine without artificial water after a year or so. Photos by Erik Skindrud Establishment versus Maintenance As simple as it sounds, identifying the purpose of an irrigation system is the most important design consideration. Is it designed for establishment, and/or is the system designed to supply regular water to the tree as it matures? The climate typically dictates the type and capacity of the system. When designing an irrigation system simply to help the tree become established, temporary irrigation with overhead spray, bubblers or drip will usually be sufficient. If a system is designed to provide regular irrigation, the water needs of the trees as they mature must be considered. In areas that receive little rainfall during the growing season, irrigation systems should be designed to provide sufficient water to the trees during initial establishment, and to encourage development of healthy, vigorous root systems as they grow. The next challenge is to estimate the water needs of a particular tree. This can be tricky because sufficient scientific data regarding water use is not available for most species. Complicating matters even further, different species have vast differences in their watering preferences. Soil type and climate conditions will also influence irrigation scheduling and water usage. All too often, enough water is provided for the tree when it is young, but as it matures it becomes stunted or stressed. The California Cooperative Extension Service has spent thousands of hours working with horticulturists and landscapers to develop a simple method for estimating plant water needs in California. Their work is a good starting place for much of the Southwest.
These are facts that nursery growers know well. Contractors who don?EUR??,,????'?????<
A basic understanding of the structure of a tree?EUR??,,????'?????<
How far beyond the drip line the roots spread horizontally, and where within this vast network of roots the most water is absorbed, are closely related. Generally speaking, tree roots will extend somewhere between one and one-half, to four times the diameter of the tree?EUR??,,????'?????<
A thorough understanding of compaction is critical to designing an irrigation system that meets the water needs of a maturing tree. Compounding this problem are the typical situations found in most urban plantings?EUR??,,????'?????< In an ideal situation, the irrigation designer will have input on the planting details for all installations. A sound irrigation design and proper planting will help ensure trees receive sufficient irrigation in order to develop healthy root systems. Well-developed root systems will thus produce healthier trees with fewer diseases and insect problems. Strong roots also provide anchors to prevent trees from blowing over in a strong wind. While creating a well-developed root system in urban settings is difficult to achieve, there are innovative ways to accomplish the objective. A more serious problem sometimes exists in a retrofit situation where an existing spray irrigation system (as used for turfgrass) is replaced with a low-volume irrigation system. Arborists have long debated the appropriateness of planting trees in turf areas. An intelligent irrigation designer will leave this age-old debate to the arborists, and determine whether the sprinklers for the turf will provide sufficient water. Trees planted in turf areas that receive water from overhead sprinklers are usually shallow rooted and compete with the turf for available water and nutrients. Most turfgrass roots are shallow, fibrous, and absorb water more quickly than the trees. This leaves trees with the table scraps, instead of the main course. To prevent this from happening, a separate irrigation system should be designed for the trees to provide the water to their deeper rootzones.
In an ideal situation, the irrigation designer will have input on the planting details for all installations. A sound irrigation design and proper planting will help ensure trees receive sufficient irrigation in order to develop healthy root systems. Well-developed root systems will thus produce healthier trees with fewer diseases and insect problems. Strong roots also provide anchors to prevent trees from blowing over in a strong wind.
While creating a well-developed root system in urban settings is difficult to achieve, there are innovative ways to accomplish the objective.
A more serious problem sometimes exists in a retrofit situation where an existing spray irrigation system (as used for turfgrass) is replaced with a low-volume irrigation system.
Arborists have long debated the appropriateness of planting trees in turf areas. An intelligent irrigation designer will leave this age-old debate to the arborists, and determine whether the sprinklers for the turf will provide sufficient water.
Trees planted in turf areas that receive water from overhead sprinklers are usually shallow rooted and compete with the turf for available water and nutrients. Most turfgrass roots are shallow, fibrous, and absorb water more quickly than the trees. This leaves trees with the table scraps, instead of the main course. To prevent this from happening, a separate irrigation system should be designed for the trees to provide the water to their deeper rootzones.
As simple as it sounds, identifying the purpose of an irrigation system is the most important design consideration. Is it designed for establishment, and/or is the system designed to supply regular water to the tree as it matures? The climate typically dictates the type and capacity of the system. When designing an irrigation system simply to help the tree become established, temporary irrigation with overhead spray, bubblers or drip will usually be sufficient.
If a system is designed to provide regular irrigation, the water needs of the trees as they mature must be considered. In areas that receive little rainfall during the growing season, irrigation systems should be designed to provide sufficient water to the trees during initial establishment, and to encourage development of healthy, vigorous root systems as they grow.
The next challenge is to estimate the water needs of a particular tree. This can be tricky because sufficient scientific data regarding water use is not available for most species. Complicating matters even further, different species have vast differences in their watering preferences.
Soil type and climate conditions will also influence irrigation scheduling and water usage. All too often, enough water is provided for the tree when it is young, but as it matures it becomes stunted or stressed. The California Cooperative Extension Service has spent thousands of hours working with horticulturists and landscapers to develop a simple method for estimating plant water needs in California. Their work is a good starting place for much of the Southwest.
Other sources include local water utilities, university extension offices, and professional organizations such as The Irrigation Association?EUR??,,????'?????< .623 x RZA x Lc x ETo = EF RZA = Potential root zone of the plant at maturity Lc = Landscape Coefficient ETo = Reference ET (inches per day) EF = Emitter and Climate Efficiency To skip the math and other details, general landscape contractors may want to work with trained irrigation contractors! After estimating the water needs for plants, design the irrigation system to provide sufficient water to the active root zone area. The bottom line is, a properly installed drip irrigation system will provide a deep soaking and wet a sufficient area to ensure the development of a sound root system.
.623 x RZA x Lc x ETo = EF RZA = Potential root zone of the plant at maturity Lc = Landscape Coefficient ETo = Reference ET (inches per day) EF = Emitter and Climate Efficiency
To skip the math and other details, general landscape contractors may want to work with trained irrigation contractors!
After estimating the water needs for plants, design the irrigation system to provide sufficient water to the active root zone area.
The bottom line is, a properly installed drip irrigation system will provide a deep soaking and wet a sufficient area to ensure the development of a sound root system.
The watering schedule is another important factor. Irrigation systems for trees should be on separate zones from other vegetation in the landscape. If not, they are usually under-watered because they require a slower, deeper watering. Turf, shrubs and groundcovers have individual watering needs that must be addressed as well. Selection of the right controller is as important as the overall irrigation design.
Scheduling point source drip irrigation water management is not addressed often enough. Developing a drip irrigation schedule for point source drip irrigation, like any calculated irrigation schedule it is just a starting point. True water management is monitoring the plants health and soil moisture.
In scheduling any type of irrigation there are several pieces of information needed in order to develop a schedule. The most logical order of questions to ask are:
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Keep in mind the irrigation system and plant water needs will tell you how long to irrigate, and the soil will tell you how often to irrigate.
Soil types are another important consideration. Sandy, loamy and clay soils will require different watering considerations. When analyzing soils before designing an irrigation system, do not overlook potential ?EUR??,,????'?????<
Typically, the top layer needs to exceed field capacity before water reaches the next layer. When this happens, surface runoff or puddling is evident. The perception that the tree has received sufficient water will present itself, when very little water is reaching the feeder roots. Use a soil probe to find the actual watering pattern. When properly designed and installed, most irrigation systems can be scheduled to provide the correct amount of water.
Conventional systems deliver water at a rate measured in gallons per minute (GPM), whereas low-volume irrigation systems deliver water in gallons per hour (GPH). The most successful low-volume systems are micro-sprinklers, conventional drip irrigation and in-line drip irrigation. Micro-sprinklers are similar to conventional sprinklers, but deliver water at a much slower rate, generally about 5 to 6 GPH, allowing deeper watering with minimal runoff. Micro-sprinklers are widely used in fruit orchards.
Drip irrigation systems that trickle water through emitters generally deliver water .5 to 2 gph. Drip irrigation is perhaps the most efficient means of irrigating landscape plants if it is designed and installed correctly.
One of the hottest debates in the industry today is determining the number and placement of emitters needed to develop a healthy, well-rooted tree. Properly-installed drip irrigation will provide a deep soaking, and saturate a sufficient area to ensure the development of a sound root system. You should evenly space emitters to cover the area underneath the tree and extend them a few feet beyond the mature canopy.
Some people believe it is better to add emitters as the plant grows, but real world experience shows it is best to design for a mature size from the beginning. Even the most diligent maintenance contractor often neglects to install sufficient emitters. Wetting a larger area also encourages the tree to develop an extensive root system quickly, reducing the chance of uprooting by the wind. For trees requiring a large number of emitters, in-line drip irrigation is cost effective method to use.
Considering the cost of replacing a large tree, it is more than worth the cost and effort of installing adequate irrigation at the time the tree is planted. No matter what type of irrigation system is used, be sure the irrigated area is large enough to support the establishment and sustainability of a healthy root system.
A tree costs $50 to $500 (and up) to purchase, and as the tree matures the value of the tree grows too. Proper irrigation is the best insurance policy for urban trees.
Joseph H. Fortier, CID, CLIA, and Jerry M. Belt Jr., CLIA are principals with Mojave Water Management in Las Vegas, Nev. The authors would like to thank and acknowledge the late Jimmy Tipton for his research and inspiration.
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