Water Efficient Landscapes - Step 5

A water-wise landscape requires a minimal amount of supplemental water from irrigation. When irrigation is used, water is applied efficiently and effectively to make every drop count. Just as we zone plants in the landscape according to their different water needs, zone the irrigation system so that plants with different water needs are irrigated separately. Water turfgrass, for instance, separately from shrubs and flowers.

Using irrigation water efficiently also requires us to select the appropriate type of irrigation for the plants and for each area of the landscape. Trees and shrubs in the low water-use zone would need supplemental water only during establishment (first 8 to 10 weeks after transplanting); plants in moderate water-use zones require water only during periods of limited rainfall when they show signs of stress. For these plants, a temporary system such as a soaker hose or hand watering may be all that is required. On the other hand, high water-use zones require frequent watering and may warrant a permanent system with automatic controls. Whenever possible, use highly efficient watering techniques, such as drip irrigation.

Sprinkler Irrigation
Sprinkler irrigation may be as simple as a single sprinkler attached to a garden hose, or it may be a complex system of underground pipes and pop-up spray heads with automatic controls. A water efficient landscape uses sprinkler irrigation for watering turf where water must be applied uniformly over the entire area. For most other applications in the landscape drip irrigation is a better choice.

Many types of sprinklers are available for use in the landscape. Permanent systems with pop-up type spray heads are most common. They are installed underground and rise above the ground surface to operate. Some are designed for use in turf (2 to 3 inch pop-up height); others are designed for use in beds of taller plants (6 to 12 inch pop-up height). Some sprinkler heads are designed for watering small irregularly shaped areas. These typically have a radius of 15 feet or less. Others, like rotary sprinkler heads, wet a radius of 20 to 50 feet and are used to irrigate large areas. Most sprinklers are available in either full-circle or part-circle models and most have an adjustable radius for watering irregular areas.

Proper Design Is Important
The installation of an efficient sprinkler system begins with good design. The system must be capable of applying water uniformly over the desired area with minimal overspray into adjacent areas.

Choosing the appropriate sprinkler for a given area is important, but equally important is the location and spacing of sprinklers. It is usually desirable to place part-circle sprinklers along the boundaries of the irrigated area. This allows uniform watering along the edges while avoiding wasteful overspray onto buildings, paved areas and other adjacent areas.

Proper spacing of sprinklers is crucial in achieving uniform water application. Sprinklers that do not overlap adequately will waste water by applying too much water in some areas and not enough water in others. On the other hand, spacing sprinklers closer than required increases the cost of the system and wastes water. In general, spacing between sprinklers should be about 50 percent of the wetted diameter. For example, sprinklers with a wetted diameter of 80 feet should be spaced 40 feet apart.

Where part-circle sprinklers are used on the same zone with full-circle sprinklers, the sprinklers should be carefully selected to achieve a "matched precipitation rate." A half circle sprinkler will only water half as much area as a full circle sprinkler; therefore, it should only discharge half as much water. If a full-circle sprinkler discharges six gallons per minute, then a half-circle sprinkler should deliver three gallons per minute and a quarter-circle sprinkler one and one-half gallons per minute. Most manufactures offer sprinklers with matched precipitation rate (MPR) nozzles.

One other important aspect of proper design is pipe sizing. Selection of pipe sizes should be based on the flow rate through the pipe. If pipes are too small, excessive pressure losses occur. This causes some sprinklers to apply more water than others and results in nonuniform application and waste of water. Additional information on pipe sizing and irrigation system design is available in Georgia Cooperative Extension Service Bulletin B 894, Lawn and Garden Irrigation Design, as well as design manuals available from the sprinkler manufacturers.

Check the Application Rate of Your Sprinkler Systems
Application rate is the rate at which a sprinkler system applies water to the soil surface, measured in inches per hour (in./hr.). If application rates exceed the intake capacity of the soil, then runoff occurs. Problems with runoff are more likely to occur in clay soils, which have a low intake capacity.

Rotary sprinklers usually have application rates of 0.25 to 0.50 inches per hour and rarely cause runoff. Spray heads, on the other hand, typically have application rates between 1 and 2 inches per hour and may cause run-off on heavy soils, especially where slopes are greater than 10 percent. If run-off occurs, turn the system off for an hour or two to let the water soak in, and then apply the remainder of the water.

Determine application rate of a sprinkler system by placing three or four rain gauges at random on an irrigated area for a predetermined length of time (usually one hour). By knowing the application rates of your sprinkler system, you will know how long to operate the system to apply a given amount of water and will avoid wasting water. Average water level within the gauges is a measure of the output of the system (inches per hour). Repeat this procedure in each sprinkler zone, particularly if different types of sprinklers are used on different zones.

Adjust Sprinkler Heads as Needed
Improper adjustment of sprinkler heads not only wastes water but also may damage buildings or cause accidents if the water is allowed to spray onto buildings, public streets or sidewalks. Carefully adjust the radius and arcs of part-circle sprinklers to prevent undesirable overspray. Check the system several times during the year to ensure proper adjustment.

Drip Irrigation
Drip irrigation, also called trickle or micro-irrigation, applies water slowly and directly to the roots of plants through small flexible pipes and flow control devices called emitters. Drip irrigation uses 30 to 50 percent less water than sprinkler irrigation and usually costs less to install. Apply water directly to the root zone to minimize evaporative water loss and run-off. For maximum water-use efficiency, use drip irrigation on trees, shrubs and flowers in the high and moderate water-use zones of the landscape. Several types of drip irrigation systems can be adapted to suit a variety of applications, from watering individual trees and shrubs to beds of annuals, herbaceous perennials or ground covers.

Components of a Drip System
In a drip system, water is distributed to the plants through small, flexible plastic pipes (3/8 to 3/4 inch in diameter) and emitters or through perforated or porous pipe. Emitters may be purchased separately from the tubing and placed in the line wherever watering is desired. Another option is to purchase drip tubing with emitters already installed at the factory, usually spaced 12 to 24 inches apart. Most emitters will discharge water at a rate of 2, 1 or 2 gallons per hour at a pressure of about 20 pounds per square inch.

Perforated or porous pipe discharges water along its entire length to wet a continuous strip. By spacing the pipe 12 to 18 inches apart, wetting a solid area is possible. It is a good system for closely spaced plantings of annuals, herbaceous perennials or groundcovers.

Most drip systems will use PVC pipe for main lines and polyethylene tubing for distribution lines. Polyethylene tubing is flexible, easy to cut, and can be connected without glue or clamps. Install emitters by punching a hole in the polyethylene tubing and snapping the emitters into place.

The drip system must have a main valve to turn it on and off. It may be an automatic electric valve connected to a controller or a manual gate valve. You can also connect the drip lines directly to an outside faucet. However, when connecting the system directly to the faucet, use an automated timer to turn the system off after a preset time. Otherwise, you may forget and leave the system on for several days.

Two other necessary components for a drip system are a filter and a pressure regulator. A drip system uses small passageways to control the rate of water application, so even tiny particles suspended in the water could cause clogging problems. To prevent clogging, use a screen filter with a 150 to 200 mesh screen.

Most drip systems are designed to operate at a pressure of about 20 psi, (pounds per square inch). Household water pressure typically ranges from 40 to 100 psi. A pressure regulator installed immediately after the filter in the main line will reduce the pressure in the line and ensure efficient operation of the system.

Which Drip System Is Best?
Because so many different types of drip irrigation components exist, trying to choose the best system for a particular application is often confusing. The best advice is to keep it as simple as possible and try to wet only those areas where the water can be taken up by the roots of the desired plants.

For trees and shrubs, using a system in which you can insert emitters wherever water is needed is generally best. The number of emitters per plant and flow rate (gallons per hour) per emitter depend on the size and type of plant. Generally, the larger the plant, the more water it requires. The following is an example of how emitters might be installed based on plant size: During very dry weather, this system would need to run about three times per week for four hours to supply the optimum water needs of the plants. Keep in mind that some species require more water than others. Consider this when installing emitters.

For watering annuals, perennials and ground covers, it is usually necessary to irrigate a solid area. This can be done using emitter lines with emitters spaced every 12 to 18 inches. By placing emitter lines 12 to 18 inches apart, a uniform wetting pattern can be achieved. Perforated or porous pipe spaced every 12 to 18 inches apart can also be used. In sandy soils, the lines will need to be closer together than in tighter soils. In annual flowerbeds, the drip lines can be laid aside during bed preparation and replaced afterwards.

A similar method of watering uses small sprinkler heads called microsprinklers, instead of emitters. All other components are identical to drip irrigation, including the polyethylene distribution lines. Microsprinklers spray an area 3 to 12 feet wide and are used for trees and shrubs or beds requiring complete coverage. Microsprinklers may be prone to vandalism and are not quite as efficient as emitters, but they do provide an economical method of achieving uniform watering.

In landscape applications, drip irrigation tubing is usually installed on top of the ground and concealed beneath mulch. This makes the system easy to install and service. However, if vandalism is likely, the tubing can also be installed 4 to 6 inches beneath the soil surface with small microtubing (1/8 to 1/4 inch) protruding to the surface. Running the microtubes above ground will allow for easy inspection and will prevent dirt from siphoning back into the emitters and clogging the system.

Guidelines for Irrigating the Landscape Establish Irrigation Objectives
In a water efficient landscape, your goal is to minimize the amount of supplemental water applied to the landscape. Therefore, routine irrigation is necessary only in the high water-use zones of the landscape. Occasional hand watering or a portable irrigation system, such as porous pipe, would be used as needed in the moderate water-use zones, while established plants in low water-use zones would receive only natural rainfall and no supplemental irrigation water.

Operate Sprinklers During Proper Times
Time of application affects water-use efficiency. The best time to irrigate with sprinklers is between 9 p.m. and 9 a.m. (Remember to take into consideration any water restrictions that may be in effect.) During this time, less wind and lower temperatures generally occur; therefore, less water is lost to evaporation. Irrigating during the evening after dew develops (9 p.m.) and before it dries in the morning (9 a.m.) does not increase disease problems. Drip irrigation systems can be operated any time of day because evaporative water loss is not a problem, and the foliage stays dry.

An Automatic Controller Helps Save Water
An automatic controller attached to the irrigation system turns the system on and off and controls the water flow through the various zones according to a preset time clock. It allows you to set the length of time each zone operates as well as the days of the week and time of day the system operates. However, an automatic controller does not relieve you of the need to closely monitor its operation. Controllers should be reprogrammed frequently during the growing season because water needs change from week to week.

A rainfall sensor attached to the controller detects rainfall and prevents the irrigation system from operating if significant rainfall has occurred. Another type of sensor measures soil moisture and overrides the system when soil moisture is adequate. Sensors are especially useful if the system cannot be monitored and adjusted regularly.

Many different types of controllers are on the market. Make sure you get one with the features you need. When managed properly, an automatic controller can pay for itself in reduced water usage, cost and labor.

Hand Watering
Hand watering is not just for newly planted ornamental plants. It is also an effective and efficient way of applying water to selected plants that show signs of stress during dry periods. The direct application of water to the base of the plant, provided it is applied slowly enough to be absorbed by the soil, uses less water and is more efficient than sprinkler irrigation. To avoid runoff when using the hand-held hose, use a nozzle that divides the spray into rain-size droplets. Some nozzles have built-in spray pattern adjustments.

When watering by hand, apply about 5 gallons of water per 10 square feet, which is approximately the amount of water delivered by a 5/8 inch garden hose operating one minute at medium pressure. Watering small shrubs (less than 4 feet in height) for one minute with the handheld hose should suffice. Larger shrubs (4 feet and up) will require slightly more water. Increase the watering time by 15 seconds for each foot of height exceeding four feet. For large trees, apply about 6 or 7 gallons for each 10 square feet of canopy area. For best results, check the output of your faucet by determining the number of seconds to fill a one-gallon jug and then estimating output per 60 seconds. If runoff occurs before you have applied the correct amount of water, move on to another spot and come back after the water has soaked in.

Irrigating Turfgrass Turfgrasses used in Georgia can survive seasonal dry periods without irrigation and therefore can be used in any water-use zone. In moderate water-use zones, a turfgrass would be irrigated only when it shows signs of moisture stress. Turf under water stress will appear a dull bluish green color, the leaf blades will roll inward, and footprints will remain on the grass after walking over an area. Irrigating turf in the moderate water-use zones with a portable lawn sprinkler within 24 to 48 hours of these signs will generally prevent serious loss of turf vigor while maximizing water-use efficiency.

Under optimum growing conditions (high water-use zone), turfgrasses use 1 to 12 inches of water per week during hot dry weather. Dividing this amount into two applications per week, applying 2 to 3/4 inch each time, usually works best. Never apply more than one inch at a time because this will likely result in runoff or deep percolation below the root zone. Early or late in the season when temperatures are cooler, irrigating only once per week is usually adequate. Never water grass daily except during establishment. Daily irrigation with small amounts encourages a shallow root system and reduced drought tolerance. Because roots generally grow where the soil is moist, a shallow root system also prevents efficient uptake of plant nutrients. Shallow, frequent irrigation increases evaporative water loss from the soil.

Irrigating Trees and Shrubs
Woody ornamental trees and shrubs have a deeper, more extensive root systems than turfgrasses or herbaceous ornamental plants. The root system of a mature tree, for instance, extends two to three times the canopy spread and may go down several feet into the soil. Woody plants, therefore, can extract moisture from the soil even when the soil surface appears bone dry and can survive long dry periods without supplemental irrigation.

Use drip irrigation on trees and shrubs in the high water-use zones of the landscape. Locate the emitters near the drip line of plants where the concentration of absorbing roots is the highest. During extended dry periods, operate the system two to three times per week. Run the system long enough to thoroughly wet the soil 18 to 24 inches deep. Regular and thorough watering of newly planted trees and shrubs will encourage good root establishment and greater drought resistance. See "Appropriate Maintenance" for suggestions on survival watering during drought or restrictions.

Irrigating Herbaceous Ornamentals (Annuals and Perennials)
Herbaceous ornamentals vary widely in their tolerance to drought. Some will perform adequately with a minimum of supplemental water while others require close attention to soil moisture. Irrigation can be provided most efficiently if the plants within a bed have similar water needs. Herbaceous ornamentals generally have a shallower root system than woody ornamentals and are among the first plants in the landscape to show water stress during dry periods. Water these plants once or twice a week and use drip irrigation whenever possible. If you can not water because of restrictions, remember that these plants are less costly to replace than trees and shrubs.

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