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DESIGNING YOUR DRIP IRRIGATION SYSTEM
GETTING STARTED
The first step is to identify the areas of your garden you wish to water with drip irrigation. Although you may not want to use drip irrigation everywhere, it is not limited to raised beds and row crops. Drip irrigation is also an excellent way to provide water in perennial borders, foundation plantings, hedgerows, irregularly shaped beds, orchards, isolated planting areas, narrow planting areas, and lawns. In many landscapes where there is already an overhead sprinkler system, it is easy to convert all or part of the overhead system to drip. A good drip irrigation system uses less water than an overhead system, and usually needs far less maintenance.
MAKE A DIAGRAM
A good drip irrigation system begins with a diagram of the garden.
A good diagram has the following elements:
- the location of the water outlets;
- garden areas with outside dimensions;
- a general description of the plants within each, i.e. vegetables, roses fruit trees, annuals, perennials, etc.;
- hardscape areas such as sidewalks and driveways which may affect the installation of irrigation lines;
- changes in elevation;
- water output from your water source measured in gallons pr minute (gpm).
Hardscape areas such as patio bricks, driveways, and sidewalks can be handled in several different ways. Sometimes paving, such as bricks, can be lifted to install a supply line beneath it.
Frequently a process called hydrojetting is a quick and easy way to bore holes beneath sidewalks. Hydrojetting is done by digging holes on either side of the sidewalk to just beneath the concrete (usually 6-12"). A nozzle is attached to a hose end and at "jet" setting, the water is pushed at high volume through the soil beneath the sidewalk, excavating a passage for drip tubing.
Larger paved areas, such as driveways, often require running supply line up and over garage doors, or around the backside of a garage. In newer residential areas builders sometimes install open pvc pipes beneath drives to serve as conduit for water and electrical lines.
Changes in elevation are significant primarily for safety reasons. If the faucet where your system originates is more than 12" below the elevation of the drip tubing, you may need special backflow prevention devices to protect you from siphoning irrigation water into your household water. Ask us for further information.
To measure the water output in gpm from your faucet, hang a bucket of known volume (i.e., two or five gallon) to the faucet, turn the water on full, and measure in seconds how long it takes to fill the bucket. From this calculate the output in gallons per minute. For example, if a two gallon bucket fills in 15 seconds, your output is eight gpm.
As a rule of thumb, for every gallon of output per minute, you can operate 100 feet of drip tubing on 12" emitter spacings. If the output is four gpm, you can operate 400 feet of tubing; eight gpm will allow you to operate 800 feet of tubing and so on. If you do not have enough water output to operate all tubing at once, you may need to subdivide the system into two or more sections. These subdivisions can be operated by manual or automatic valves.
Most homes on municipal water systems operate at pressures of 40 to 60 psi. A drip system operates at 20 to 25 psi, achieved by using a pressure reducer. The drip tubing we offer needs a minimum of 10 psi to function properly. If you are on a well, using gravity feed, or simply have doubts about your pressure, the only way to find out for sure is to measure it with a pressure gauge. They can usually be obtained at local hardware or plumbing stores. We have "loaners" at the Natural Gardening Company which we will send to you for the cost of postage. Obviously we need to get these back right away for others to use. We believe the Honor System can still work.
WHAT'S YOUR SOIL TYPE?
The final consideration in designing your system is your soil type. Water moves in different ways through different types of soil. It drops almost straight down in sandy soil, and forms a large subterranean ball in clay soil. The more water spreads laterally in your soil, the farther apart your drip lines can be. In general, for continuous water throughout a bed, sandy soils need lines 12-15" apart, loamy soils need lines 15-18" apart, and clay soils need lines 18-21" apart.
DRIP IRRIGATION FOR LAWNS
With the development of in-line emitter tubing, drip irrigation for lawns is now a reality. Drip irrigation for lawns greatly reduces water consumption as it virtually eliminates loss of water due to evaporation. It totally elimiates overspray and runoff. Maintenance is reduced because there are no exposed aprts to break.
The best time to install drip irrigation in a lawn is with new lawns, before planting seed or sod. These are the basic steps:
- Amend your soil and roll so it is relatively level;
- Dig trenches 4" deep, in parallel lines (the distance between lines depends on soil type);
- Lay your drip tubing in the trenches and stake it in place using our Earthstakes;
- Make all connections to supply and exhaust lines;
- Install flush valve at far corner away from incoming water;
- Install air release valve at highest spot in emitter tubing;
- Cover tubing with soil and roll to level;
- Lay sod;
- Overhead water for about ten days so sod can root, then gradually reduce overhead watering and increase drip watering, so that within about another week the lawn is watered only by drip lines;
- Follow step 7 if you are using seed, but prolong overhead watering until all seed is thoroughly sprouted and established;
- Water daily so soil remains moist, but not soaking, at all times. Start with a base line of 15 minutes and adjust up or down based on average daily temperature, sunlight, rain, and other weather factors.
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