Water is important to the growth and survival of plants. Water comprises 70 to 85 percent of the fresh weight of most turfgrasses and landscape plants. It also functions as a transport medium and cooling mechanism and is involved in many biochemical reactions in plants. As water is lost from evapotranspiration (ET) and leaching, you must apply more water to maintain a constant supply to turfgrass and plants. Landscapes receive water from two sources: precipitation and irrigation. Some water moves upward through the soil profile to replenish water losses, but this process is normally too slow to meet turf needs. The best way to achieve a constant, reliable supply of water is to irrigate.
An in-ground, automated irrigation system makes life much easier for anyone who irrigates. Unfortunately, the convenience of time-clock irrigation promotes poor watering practices. Often, a technician sets the time clock at installation, and it remains at that setting thereafter. As a result, the automated cycle doesn’t accommodate the landscape’s actual water needs.
Plant water requirements vary, depending on the species, environmental conditions and cultural practices. These factors, which include relative humidity, day length, temperature, wind speed, mowing height and fertilization, influence ET.
Transpiration is the process by which turf and other plants absorb water from the soil and transport it from roots to leaves to the atmosphere. By monitoring transpired water and water evaporated from the soil, you have a fairly good indicator of how much water plants use each day.
Because both environmental and cultural factors influence ET, water use is never constant. For example, in a study at Kansas State University, tall fescue ET ranged from 0.13 to 0.42 inches per day between July and August. This variability of turf ET emphasizes the importance of adjusting irrigation amounts to meet current demand. It also demonstrates that you can save water and improve irrigation efficiency by monitoring turf water use.
You should only irrigate your landscape when it needs it. Ideally, you should irrigate when the first symptoms of wilt appear. Wilt is the visible loss of turgidity expressed by drooping, folding or rolling of leaves. You can first detect wilt in turfgrass by a blue-green or slate-colored appearance. “Foot printing” or loss of elasticity of turf is another visual symptom of wilt. Allowing turf to proceed through the wilting stage and into a more severely stressed condition may result in summer dormancy or, in extreme cases, turf death.
Irrigating at the onset of wilt may not be practical in all cases, because landscapes may be in use during the day and cannot be irrigated without interrupting use. In such cases, you must use other methods to predict water need, for example the consumptive-use method or soil-moisture measurements. The consumptive-use method estimates ET from a turf stand (see boxed information, “Determining landscape-irrigation requirements,” page 64, for specifics on landscape-plant water needs). It is based on water losses from an evaporation pan. However, for this method to be effective, you must make preliminary calibration of evaporation-pan results with actual turf wilting.
Some moisture measurements involve either direct measure of soil moisture through oven drying and weighing or indirect methods that measure the soil-moisture tension. The gravimetric method of determining soil-water content involves measuring soil’s weight loss after heating it in a warm oven for 24 hours. Follow this procedure for determining weight by the gravimetric method:
- Take a soil sample from the turf area at the onset of wilting and place it immediately in a sealed moisture-proof jar.
- Weigh the moisture tin in which you’ll be placing the soil sample and record its weight.
- Fill the moisture tin about three-quarters full of soil. Weigh it and record the weight.
- Label the sample with a piece of paper.
- Place the sample in a 220°F oven for 24 hours.
- Remove from the oven, cool, remove the paper label and reweigh the dried sample. Record this weight. Subtract the weight of the moisture tin from the actual wet and dry weights of the soil.
- Calculate the percent of water content:
weight loss after drying X 100 weight of oven-dried soil
= % water content
- After a thorough rain or irrigation on the area from which you took your first sample, wait a set period (12 hours if the area has sandy soil and 24 hours if the area has clay soil). Then take new samples of soil from this same area. Repeat Steps 1 through 7 with these new samples. They will indicate the water content at field capacity.
- Calculate the irrigation point using the following formula
|[(Percent water content at field capacity||÷ 2|
|percent water content at wilting point)]|
Irrigate when the soil-moisture content reaches the irrigation point.
You can irrigate your landscape at any time during the day. However, the ideal time is in the early hours of the day. At this time, wind is minimal, and you reduce water losses. Also, irrigating at this time gives water a better chance to infiltrate into the soil before it is lost to evaporation.
Watering at night or in the evening is a second choice to morning irrigation. Water loss to evaporation can be minimized at this time, but the moisture remaining on plant leaves overnight creates a condition conducive to disease development. Nevertheless, in some cases, such as on golf courses, night irrigation may be the only way in which you can practically water turf or a landscape without interrupting its use. Night irrigation is especially practical with automatic irrigation systems.
Daytime is the least preferable time to irrigate. Evaporative losses are high, and wind also may be during the day. Turf temperature normally reaches a peak at 2 p.m. A light application of water (syringing) at this time will lower turf temperature and prevent wilting. However, keep in mind that syringing is not intended to provide water to turf roots. Instead, it is simply meant to cool turf by evaporating water.
The rate of irrigation always should be lower than the rate of infiltration. Allowing irrigation rate to exceed the infiltration rate results in water runoff. Slope also can influence runoff, because a steep slope encourages runoff. In addition, soil factors such as texture, structure and, perhaps, thatch influence infiltration rate.
Many tools are available to help you specifically determine your irrigation rate. They include soil-moisture monitors, weather stations and using ET with turfgrass coefficients. Consider each:
Moisture sensors. These can provide the following benefits:
- Reduce water use
- Save money because of lower water use
- Reduce leaching fertilizers past the root zone
- Reduce runoff
- Minimize damage to pavement, sidewalks and buildings
- Reduce client/customer complaints of over-watering while it’s raining
- Decrease drainage problems
- Provide lower maintenance expenses.
Many different types of soil-moisture sensors are used in landscaping. The most common are tensiometers, solid-state tensiometers, electrical-resistance blocks and point-contact blocks. Tensiometers measure the matrix potential or capillary tension in the soil. This is similar to the force a root must exert to take water from the soil.
Electrical-resistance blocks measure the matrix potential indirectly. They consist of electrodes that are embedded in gypsum or plastics. As moisture content increases between the electrodes, electrical resistance decreases. You can calibrate electrical-resistance measurements to matrix potential for the soil in question. Point-contact blocks have many electrodes that measure moisture contact at each point.
You can control residential and small commercial sites with one or two simple sensors or one sensor at each automatic-control valve. You should be able to adjust these sensors at the control valve or the automatic controller.
Large commercial sites, such as parks and highways, require more sophisticated sensor systems. These systems should meet the following criteria:
- Sensors are adjustable from the automatic-controller location
- The system provides manual or automatic sensor override
- The system should need little sensor maintenance
- Equipment can withstand freezing soils (if required)
- Sensors are corrosion resistant.
Today, you can use soil-moisture sensors with several central/satellite control systems. It is even possible to add some sensors to your existing irrigation system with little additional wiring. (See Figure 1, above left, for information on installing a moisture sensor.)
Weather stations. A weather station can provide you with the climatic parameters you need to calculate ET. The most common ET-rate equations in landscape irrigation are Penman and Penman-Monteith. Both of these equations originally were calibrated for clipped grasses. They are based on 1-day’s data. Because turf’s root zone is so shallow—and hold-over moisture insignificant—1 day is a critical time element.
Nevertheless, keep in mind that the following factors all can affect whatever equation you use:
- The area’s historical climatic data
- The time for which you need ET rates
- Your location
- Your plant type and its condition.
Specifically, when using the Penman equation, you must have climatic information on:
- Maximum and minimum temperatures (°Celsius)
- Relative humidity (percentage)
- Wind movement (kilometers per hour)
- Net radiation (calories per square inch).
To get this information, you must have a data logger. This equipment—basically a programmable computer—is located on the pedestal of the weather station. It queries sensors, storing the data for later retrieval. These sensors include:
- Anemometer to measure wind speed
- Tipping-bucket rain gauge to measure rainfall
- Pyranometer, which monitors solar radiation
- Temperature probe, which tests for maximum and minimum temperatures
- RH probe, for relative humidity.
Other factors you may find useful to monitor include:
- Soil temperature
- Wind direction
- Soil moisture
- Water quality
- Pump pressure
- Pump flow
- Pump power.
You can provide power for your station from a 110-volt AC source. Or you can use solar power or a 12-volt DC wet-cell battery.
Locate your weather station away from obstructions, such as buildings or trees. Primarily, don’t let the irrigation system throw water on it, and don’t shade it from the sun or shield it from the wind (see Figure 2, page 57).
ET and turfgrass coefficients. As mentioned previously, by monitoring transpired water and water evaporated from soil, you have a fairly good indicator of how much water turf uses each day: ET. Several tools are available available to help you monitor turf’s water use: atmometers and empirical models.
√ Atmometers. An atmometer is any tool used to measure the evaporating capacity of air. The most well-known example of an atmometer is the evaporation pan. Daily measurements of evaporation from the pan are converted to turf ET with a crop coefficient, or multiplier: pan evaporation x crop coefficient = turf ET. Traditionally, the evaporation-pan crop coefficient for cool-season grasses is about 0.80, while that for warm-season grasses is 0.60. In other words, if 1 inch of water evaporates from a pan, you should irrigate a cool-season turf with 0.80 inch of water and a warm-season turf with 0.60 inch of water. √ Empirical models. These models are equations that incorporate climatic data, such as temperature, solar radiation, wind speed, etc., to generate a predicted ET value. Examples of some commonly used equations are the Penman, Penman-Monteith and Jensen-Haise. Modern irrigation systems typically use a weather station and accompanying software that allow the operator to estimate ET using an empirical model.
Irrigation systems are meant to uniformly distribute water to an area at a rate that does not exceed the infiltration rate of the soil. An irrigation system is comprised of sprinkler heads, pipes, valves and a pump or city water source. When designing an irrigation system, you should give consideration to the compatibility of all components. Pipe size and length, valve size, and the size and number of sprinklers comprising an irrigation system must be compatible with the pumping system. All components of the system are meant to operate at specified flow rates and pressure, and their use beyond pressure and flow limits will result in unsatisfactory performance.
Irrigation systems vary in complexity and cost. Homeowners use simpler systems. They include flexible hoses with movable sprinkler heads, which may be supplied with water from a municipal source. More complex systems include fixed irrigation systems, which may be completely automated. Aside from initial cost, in planning an irrigation system, you should consider practical management of the system to supply water when it is needed. Turf managed under high intensity requires a significant amount of manpower to meet turfgrass requirements if you use a manual irrigation system, whereas automatic irrigation systems can save considerable manpower for other tasks.
Three major sprinkler-head types are used for turf irrigation: oscillating, rotary and spray.
Oscillating or wave-type sprinklers. Residential customers are the primary users of these types. They are best suited to relatively small areas. Water is delivered through holes in an oscillating arm. Water delivery rate is slow with these types of sprinklers, and they are readily affected by wind.
Rotary or impact-driven sprinklers. These are the most widely used heads on professional turf because they are best-suited for large turf areas. Coverages range from 40 to 200 feet in diameter. Rotary sprinklers deliver water in one or more streams and rotate by means of hydraulically driven gears or by impact. Impact-driven sprinklers rely on the power of the water stream to impact a spring-loaded arm and move the sprinkler head. Repeated impact drives the spring-loaded arm and moves the head in an entire circle. Part-circle impact heads are also available, as well as adjustable heads. Rotary sprinkler heads deliver the greatest amount of water nearest the water source, and the amount of water delivered diminishes as the application approaches its periphery. When you position heads properly to provide sufficient overlap, you can achieve relatively uniform coverage. Wind, however, will distort the pattern of rotary sprinkler heads especially with heads covering a large area. The larger the water stream’s coverage area, the more susceptible the stream is to wind. Nevertheless, rotary sprinklers are the most economical and most efficient on large areas.
Spray-type sprinkler heads. Also referred to as fixed heads, landscapers use these most frequently on relatively small turf areas. The area of coverage is between 16 and 24 feet for a single head. You’d typically space heads 10 to 24 feet apart to provide overlap and uniform coverage. In contrast to rotary sprinklers, spray heads discharge water in all directions at once. The nozzle orifice of this type of sprinkler head is designed to provide a predetermined radius of coverage and flow at a specified pressure.
Adjustable and part-circle fixed heads also are available. Spray-type heads are least affected by wind. These heads also apply water at a rapid rate and may not be suitable on heavily compacted soils. In addition, the area covered by individual spray heads is relatively small, thus necessitating more sprinkler heads to cover an area in comparison to rotary sprinklers.
From the previous discussion about sprinkler-head characteristics, it is evident that sprinkler heads differ in distribution pattern, area of coverage and response to wind. The ultimate goal in designing a sprinkler system is to achieve uniform water distribution. Because the amount of water applied per unit area decreases with distance from the sprinkler head, it is important to overlap coverage among adjacent sprinklers. Wind also may influence the spray pattern, and you must take it into consideration when determining spacing.
Spacing is generally referred to in terms of a percentage of the wetted area.
|Percent spacing =||Distance between sprinklers||x 100|
|Wetted diameter of sprinklers|
Percent overlap = 100 - percent spacing
For example: 70 percent spacing = 30 percent overlap of spray patterns.
|70 percent spacing =||42 ft||x 100|
30 percent overlap = 100 - 70
You can use several different approaches to spacing in designing an irrigation system for uniform coverage. Irrigating with a multiple-row system is more preferable than with a single row of heads, because distribution is more uniform. Multiple-row system designs include square-spaced and triangular-spaced heads. Generally, square-spaced heads should have 50-percent spacing, and triangular-spaced heads should have 60- to 70-percent spacing.
PRESSURE AND DISTRIBUTION PATTERNS
Correct irrigation-head placement starts by understanding the available operating pressure at the site and understanding irrigation-distribution patterns. Manufacturers design irrigation heads to work within certain pressure ranges. Incorrect pressure has a direct effect on how evenly and how far the irrigation system distributes the water. A pressure variation of only 5 psi can change the coverage radius of an irrigation head by 1 to 2 feet. Therefore, it is critical to make sure the pressure at the irrigation head is what the designer intended it to be.
What happens when you operate an irrigation head above the suggested pressure? You distort the distribution pattern and cause excessive wind drift and overspray. As mentioned, you also reduce the effective throw of that head (see Figure 3, page 58). Operating a head below the manufacturer’s pressure recommendations also distorts the pattern, leaving turf areas with donut-shaped dry spots. If necessary, you may need to adjust flow controls or install pressure-compensating devices to achieve the proper pressure.
Another consideration is the irrigation-head’s distribution pattern. Irrigation distribution patterns influence spacing patterns, wind effects and system uniformity. Manufacturers, however, do not create all heads equally or with the same distribution pattern. You can produce different distribution uniformities for the same system, in fact, simply by selecting a different head—even when manufacturers claim the same radius, gpm and precipitation rate for that head. When that happens, the head with low distribution uniformity does not spread water evenly. This results in your running the irrigation system longer to make up for weak areas in the coverage. This means more water, higher water bills and saturated spots in areas with the heaviest coverage. Therefore, it is always a good idea to select irrigation heads with the most appropriate distribution patterns for a given application and ones with high uniformities.
A good way to evaluate irrigation uniformity during the design phase is with a computer program called SPACE (Sprinkler Profile And Coverage Evaluation). This program uses densograms to model irrigation-head performance using data collected by the Center for Irrigation Technology from single-leg or full-grid catchment- pattern tests. The program produces irrigation profiles and densograms for single heads and allows you to check uniformities for various square or triangular spacing patterns. A program called Hyper-SPACE allows you to evaluate almost any type of irrigation head layout even if the spacing is not uniform. (To obtain a copy of the SPACE or Hyper-SPACE software programs, contact the Center for Irrigation Technology, California State University, 5370 N. Chestnut Ave., Fresno, CA 93740-0018, 209/278-2066.)
The rule of thumb in irrigation-head spacing is head-to-head spacing. You use this rule to account for wind effects during irrigation. Manufacturers’ recommended spacing typically starts at 60 or 65 percent of the irrigation diameter. This drops to about 50 percent (head-to-head) for conditions where you might expect the wind to exceed 4 to 8 mph. For some irrigation-head types, you must modify this spacing higher or lower to achieve better distribution uniformities and avoid excessively wet or dry patches.
An important consideration is that different heads operated under the same conditions produce different uniformities. Some manufacturers design irrigation nozzles that produce a higher degree of uniformity than others do. As the industry places more emphasis on water conservation, it will become more important to select irrigation heads that produce the highest degree of uniformity possible for a particular application. For now, try and find out as much as you can about the irrigation heads with which you work and what their individual strengths and weaknesses are.
Once you select the correct irrigation head, you need to consider proper placement. Accurate field staking is the single biggest error in the design or installation of a new irrigation system. Yet, maintaining consistent spacing is the only way to maintain a high degree of uniformity. After all, spacing that varies by as little as 1 foot (less than 7 percent) on a 15-foot radius head will change the average precipitation rate between heads by more than 20 percent (see Figure 4, left).
If you’ve never installed an irrigation system, don’t be unsettled by the myriad details involved. To install a system successfully and within budget does require attention to specifics—from design to maintenance. However, with the basic facts at hand, you’ll have a starting point from which you can ask more detailed questions.
Obviously, the most basic question you first must ask is, “Where will the water come from?” Then you can move on to consider the more complicated aspects. These include system, design, pipe considerations, system options, component selection and the as-built drawing’s importance.
WATER SOURCE AND PRESSURE
One of the first aspects to consider when installing an irrigation system is the water source. It can be from a municipal water supply, a well or a pond.
If a municipality provides the water, it is important to know the size of the water service and the pressure delivered to the site. Also you should check with the water purveyor for local codes or regulations.
If tapping into a main line in the street, your local water utility can provide the information needed.
Before ordering materials for the irrigation system, you should verify the actual water pressure to make sure it matches the rate the water company says it does.
You can determine the pressure on a small line with a simple gauge that measures the static pressure at a particular point in the water supply line. On large projects, it may be wise to do a flow test that tells you about gallons per minute and the drop in pressure over the landscape.
If you are installing a system on a golf course, you probably will need to construct several water retention areas or ponds as your water source. The size of these ponds usually is determined by the course’s irrigation requirements during the months of highest water consumption, as well as the time constraints of the site during those months. An example of time constraints might be just how long the system can be on without interfering with players on a golf course.
If you are installing a system on a residential site, you’ll most likely tap into the homeowner’s water supply. In most cases, doing so is fairly routine. You probably won’t even need a pump to get the appropriate water pressure. But to be sure, you’ll want to determine the demand for water and the amount of water and pressure available. For example, if the area is hilly—even on a small residential site—you may need a pump to supplement pressure coming into the site to serve the upper areas requiring irrigation.
Before you can begin designing the system, you must take several factors into consideration. Think about types of plantings, sun exposure, slope, soil type, average rainfall in the area and design of the landscape itself.
Then you can choose the type of pipe—a relatively easy task because few choices are available. Of the two main options, polyvinyl chloride (PVC) pipe is typically preferred over polyethylene (poly) tubing because of its strength and durability, especially on pressurized lines.
In warmer climates, such as California, installers use PVC for both main and lateral lines. In cooler climates where soil is subject to quick-freezing conditions, however, PVC is used for main lines and poly for the lateral ones, at least in residential and small commercial systems. The reason for this: Even though PVC is stronger, it also is more rigid. Thus, it is less flexible than poly tubing and cracks more easily.
Laying pipes down deep also can help avoid problems in cold weather. An irrigation consultant can give you specific guidelines on how deep to lay piping in your area of the country and which type of piping to use. Use drain valves to empty water from pipes as another means of avoiding freeze damage.
Installing your piping is another main consideration. To install polyethylene pipe, you’ll probably want to use a vibratory plow, also called a line-puller or drop-cable plow. If using a different piping material—such as PVC—which might not be strong enough to withstand being pulled through the soil, or if the site is extra hilly, another type of trenching machine may be more appropriate.
If the soil on a site is particularly rocky, placing sand around the pipe can prevent rocks and other sharp objects from puncturing the pipe. This is usually not a problem for most installers however.
Often, irrigation consultants recommend that landscape contractors use a combination of drip irrigation and spray heads or rotors to get water to root systems. For example, on large turf areas, it usually is most cost effective to use large, gear-driven spray heads on 40-foot spacings. Then, on smaller turf areas, use pop-up spray heads. Ornamental beds are where drip-irrigation systems are usually most effective. You also will want to use them in arid areas with water restrictions.
For the very reason that drip-irrigation systems are not out in the open, they can present problems not encountered when using other irrigation systems. Too often, once landscape contractors have installed a system, home owners or maintenance personnel forget about the systems. After all, if a sprinkler head acts up, the problem is obvious. If a drip irrigation system gets clogged or a valve breaks, however, you can’t readily see it. Thus people don’t discover problems until plants begin to die. However, as long as you properly maintain and regularly inspect these systems, you probably will avoid major problems.
Picking the proper sprinklers, valves and controllers can be tricky. Many manufacturers offer irrigation components; not all of them are necessarily equal. One manufacturer may make good spray heads, but its valves or rotors may not be as good as another company’s and vice versa.
How can you make comparisons? Increasing numbers of manufacturers now provide distribution curves for each sprinkler they offer. These distribution curves chart how systems behave according to varying factors. For example, according to a manufacturer’s distribution curve, a given sprinkler with a certain nozzle will provide different coverage at 50 pounds of pressure than it will at 70 pounds.
A client or owner may not notice differences in coverage most of the time. You can be sure, however, that during a drought year when irrigation uniformity is crucial, a client or manager will notice brown spots where turf did not receive adequate irrigation. Poor irrigation system design also will show up during periods of drought. Other system components you need to consider are valves, controllers and rain or moisture sensors:
Valve selection. Valves come in plastic or brass. Which one you choose will depend on your particular situation as well as the budget. If an owner requests you use metal valves, or for other reasons a system needs a longer-lasting valve, brass should be your choice. In other situations, plastic valves are used frequently because they are less expensive. Plus, every year, manufacturers improve the quality of these products. Controllers. Though some electro-mechanical controllers are still on the market today, most installers usually purchase solid-state controllers. Electro-mechanical controllers are easier to operate and fix, but they do not offer the flexibility and sophistication of solid-state models. However, solid-state controllers can be difficult to program and require a thorough reading of the manual. In fact, most maintenance calls concerning improperly working solid-state controllers often result from homeowners tinkering with the controllers after the contractors have programmed them.
Advantages to solid-state controllers include flexibility in programming multiple starts. Multiple starts allow you to coordinate infiltration rates that more closely match soil conditions. Electro-mechanical controllers, however, typically have only one or two programs available, and you cannot cycle zones as easily on these units.
Rain/moisture sensors. With increasing concern about water conservation, rain or moisture sensors are a must. In fact, some communities require them. Rain sensors are important because they prevent irrigation systems from operating while it rains. They are simple to operate, require little maintenance and typically cost less than $40. Moisture sensors do their job by determining the amount of moisture in the soil and running irrigation systems accordingly.
Though problems have plagued these sophisticated instruments in the past, newer solid-state models work quite well. Unfortunately, rain and moisture sensors are often the first component disconnected by a homeowner or maintenance person who believes the sensor does not operate properly. You can avoid this by showing homeowners or maintenance personnel how the system works.
Make sure that an as-built drawing of your irrigation system is completed during installation. Thousands of irrigation systems throughout the country are completed each year without any record of how they actually were installed. This can make future maintenance difficult.
Though you easily can find sprinkler heads as long as they operate, valves are more difficult to locate. This is especially true if they were not originally placed in valve boxes or if grass grows over a valve box. Other system components, such as quick-coupling valves, also may be difficult to locate without a reference.
Obviously, installing an irrigation system is more complicated than described here. If you are uncertain about some aspect, ask someone who knows. Irrigation-design consultants or component manufactures can answer questions about the design and installation of irrigation systems.
IRRIGATING ANNUALS, PERENNIALS AND BULBS
By mid-July, you know the price of your floral displays, especially if the maintenance crew has been hand-watering the beds because of an inadequate or non-existent irrigation system. All too often flower beds must rely on overspray from turf sprinklers or hand watering. Installing an irrigation system may be an attractive option.
Many choices are available for irrigating bedding. Sprays, rotors, impacts, micro-sprays, microspinners and drip may all be good ways to water your plantings, depending on the situation. Let’s look at some of their specific applications.
Some plants prefer to be washed and misted daily. Others do much better with little or no water on their leaves and blossoms. If you are considering a system that would provide over-the-top watering, be conscious of the possible disease problems associated with this type of irrigation (see section on diseases, Chapter 15).
How much water to apply depends on many factors. Usually, you find out quickly if water is inadequate for summer annuals. Plants will not thrive and provide good color if they are under drought stress. Spring-blooming bulbs typically obtain enough moisture from rain and snow but, in unusually dry seasons, supplemental water may be necessary, even in the fall or early spring. Remember, just because the bulb has not yet sent leaves above ground does not mean it isn’t growing—it still needs moisture.
Avoid overwatering your beds. Plants vary in their tolerance to soggy soils, but waterlogging is bound to bring problems. Unfortunately, you cannot prevent excessive rainfall. All you can do in this case is maximize drainage and hope for drier weather.
As a rule of thumb, flowers use about 25 percent less water than turf, depending on the varieties used and the mulch around the plants. This makes it appropriate to water flowers independently. However, it is often uneconomical to separately irrigate a small isolated flower bed from surrounding lawn or shrubs. Your judgment based on training and local knowledge will serve you in deciding what type of system to install. The best choice for one site might not be the appropriate method for another. Before making blanket recommendations, study each location’s needs. The key points to consider are:
Armed with a site evaluation, you can identify potential systems that will work and price them to determine each system’s actual yearly cost. This will help make your final decision as objective as possible.
Rotors and impacts. There is a place for plastic rotors and plastic or brass impacts in large flower beds. These sprinklers water over the top of the canopy and should be on stationary risers or in pop-up canisters. Some rotors have 12-inch pop-ups available.
Sprays. Spray heads have been the most popular method of watering flowers through the years. These sprinklers have watering arcs of 15 to 360 degrees. However, manufacturers also make specialty rectangular patterns for areas such as parking strips and medians.
Plastic and brass spray heads are available in pop-up canisters that allow the nozzle to extend 2 to 12 inches above the body. You also can place them on factory risers or steel or PVC risers that add even more height.
In case a riser gets tipped over, a flex connection should be located underground to prevent it from breaking. Specialty flex risers also are available.
Microsprays and spinners. Microsprays and microspinners are low-cost options to sprays. You can get nozzles attached to individual pop-up canisters, placed in shrub adapters on risers or inserted in special risers with a small poly pipe attachment holding the micros.
Special risers that attach to poly pipe allow you to string poly pipe or drip tubing through the center of the bed. You can tee off of it with 1/4-inch poly tubing by using a barb adapter to run to each microhead location.
Most micros have a relatively flat watering pattern, which requires you to place them above the canopy in most situations. However, on tall plantings you might be able to use them under the canopy.
Even though running drip tubing with poly laterals to the individual heads is inexpensive and flexible, it only takes one big dog running through the bed to create havoc with whole system. The micro circuits also may require pressure regulation to 30 psi if static pressure is high at the delivery point. You could use pressure-regulating micros, remembering that the drip-tubing system is designed to run at no more than 50 psi.
Drip emitters. Drip emitters are a low-gallonage option with water point-applied to each plant or row of plants. The emitter exit points are critical to the operation of the system because there is no surface spreading of water. Sandy soils require narrow spacing (possibly as close as 6 inches) while clay soils allow liberal spacing (perhaps every 2 to 3 feet). If you have flowers that demand more or less water, emitter spacing and sizing can match that demand.
Low pressures of 15 to 30 psi tend to work best over a range of emitter types. The trick is to keep the pressure as constant as possible throughout each circuit. This will give uniform emission at each outlet. If pressure constancy is a problem, use pressure-compensating emitters. They cost more but they simplify your installations. Include a pressure regulator and filter (100 to 200 mesh) upstream of a drip circuit.
Drip tubing is used as the water carrier through the system. It can be left aboveground, placed under mulch or buried 2 to 3 inches below the surface. To reduce vandalism, place tubing under the mulch or ground. This will require bringing 1/2-inch poly tubing to the surface from each emitter, if you want to observe its operation. Observation is the only way (other than wilted plants) you have of knowing each emitter is working.
As stated earlier, the type of irrigation you use in your beds depends on numerous factors. As you can see, several effective options exist. In spite of the advantages of irrigation systems, hand watering still is widely practiced. The choice between hand watering and installing a system depends as much on available resources as it does on which is more effective. Both can produce satisfactory results, but installing a system is without question more labor-efficient. Remote sites or those with no water access may require watering from tanks.
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