Irrigation 101
Your complete guide to understanding Landscape Irrigation
A landscape irrigation is a system comprised of piping, an electronic timer, control valves, and water delivery heads that provide automatic supplemental watering of your plants and turf grass areas.
True need for irrigation is determined by an on site “ET” (evapo-transpiration rate). “Evapo” evaporation is the loss of moisture caused by wind, temperature sunlight etc. “Transpiration” is the loss of moisture that is utilized in the photosynthesis process of a plants or grasses natural feeding cycle.
ET rates vary by month and are measured in inches of replenishment. In Roanoke, Virginia, April and October have low ET rates-normally an inch or less. The months of July and August often exceed 7 inches of replacement need. More than likely you have observed most people’s yards and plants look great in May and start to brown out in late June or early July depending on the rainfall amounts.
Experts have determined that for best plant and grass health we should irrigate when the soil moisture level has been depleted down to the 50% level, then replenish to 100%. Think of a kitchen sponge that is 100% saturated to the point where it just stops dripping, and then you squeeze out 50 % of the water. Then, fill again to 100% (in soil management terms “field capacity”). This watering should be done in the early morning hours, when winds are light and water pressure is at its highest.
Notice we speak about plants and turf grass separately. This is because, on average, plants require only 1/3 the amount of water as do grasses. It is imperative that, when economically feasible, system designs separate all planted beds from turf grass areas. Do not let an installer tell you differently. If so you will end up with brown grass and happy plants or green grass and root rotted plants.
Now that you have a basic understanding of the science that underlies “evapo-transpiration”, the how, why and when we need to water. We must further consider the other necessary parts that make up the sum total of the “striving for perfection” lawn/plant equation. Make no mistake, an irrigation system alone can and will not provide outstanding results.
Part One: A professionally designed and installed Irrigation System.
Part Two: A “Weed and Feed” program is a must. A pre-emergent in the spring is to control unwanted weed and crabgrass germination. That in addition to a carefully orchestrated feeding program to replenish vital nutrients is a must.
Part Three: Mother Nature. You know this lady. We are not supposed to fool her; however she fools us all the time.
Irrigation System Components:
Water Source:
We have systems that employ wells, creeks, lakes and even cisterns; however the majority of our water comes from the public water supplies. In most cases, your water purveyor is a reliable and “fairly” economical source who provides uninterrupted service at a pressure needed to enable your system to function properly. Where applicable, we install sewer subtraction meters so you do not pay sewer charges on water used for irrigation.
Back flow Prevention:
If your potable (drinking) water and irrigation water are derived from the same source then, we must ensure the two never mix! We assure this by installing a Reduced Pressure Zone (RPZ) Back flow Prevention Valve. This mechanical unit monitors pressure differentials and reacts by venting if it detects a back flow or back siphon condition. In most cases, it is required by Virginia Plumbing Code. Due to the possibility the unit may vent at any time, it must be installed above ground 12” from the bottom of the vent to ground level.
While some mechanically inclined people think this bronze beauty is worthy of being a museum piece, we prefer it to be placed out of site. Also Note: this unit requires a yearly inspection by a Virginia State Licensed Tradesman accompanied by a permit. We have on staff a Virginia Board Certified Backflow Prevention Device Worker (2710-043715 exp. 4/30/2013). If required by your locality, we will procure permit and check the unit each spring during the turn on to keep you in compliance with Virginia Plumbing Code.
Pipe:
Pipe must be correctly sized for your system! Far too many installers do not observe basic physics pipe design principles and limitations. More often than not, they choose to use the smallest cheapest pipe they think they can get away with. However, this is a recipe for future disaster! PVC pipe, commonly used in irrigation systems, allows for a maximum flow rate of 5.5 feet/second. Using pipe that is undersized will cause this maximum flow rate to be exceeded. Then, scrubbing occurs and your pipe and fitting are eaten away by water from the inside out. And!!! Future additions are out of the question. What appears to be a bargain is probably not! If your potential installer can not quote by heart the 5.5ft/second rule send them packing!
Pumps:
A pump is needed if existing water pressure, or if you have a well, is inadequate to run an irrigation system. Generally, we need a minimum of 65psi at the point of connection (P.O.C). If not, we will have a licensed electrician install a 230v circuit (115v inadequate) and we will size and plumb a pump that is right for your system. One size does not fit all. Too large a pump will cavitate and destroy itself. Too small a pump is like not having a pump at all. Pumps are sized by knowing the input in gallons/minute GPM and the desired output pressure. These variables are plugged into a Pump Curve Chart and the proper size is derived from this info.
Controllers, Smart ET Controllers and Rain Sensors:
A Controller is the electronic timer that provides a signal to a control valve. When commanded by the controller the valve opens and water starts flowing to a Zone (a like group of heads). Standard Controllers are usually programmed based on educated guesses as to how much and when to water.
Smart ET Controllers get daily satellite updates and water based on true “ET” rates which are accurate to one kilometer. These controllers then take in to consideration head type, precipitation rates, plant type, root depth, soil types, micro-climate, and slope information for each zone. These are a real money saver and provide for a very healthy overall landscape. These units have made the Standard Controllers obsolete.
Rain Sensors mechanically attempt to measure precipitation and preclude watering following periods of rainfall.
Electronic Control Valves:
Valves act as an on/off switch. On the inlet side of the valve “Mainline water is ever present and waiting for the valve to open. When called for by the controller the valve opens and water begins to flow to the respective zone. Rain Maker constructs systems using valve manifolds. Multiple valves are placed together to ensure future maintenance is easily accomplished.
Water Delivery Heads:
- Rotor Heads: These units are used to cover large open spaces. Mounted at grade, as water begins to flow they pop up and the water flow turns a series of gears which rotates the top of the head where the nozzle is located. These heads can cover distances as close as 21 feet up to 90 feet. They can be adjusted from 40 degrees to 360 degrees of rotation. A typical rotor head employs a nozzle that delivers between 2 and 6 gallons per minute.
- Spray Heads: These units are designed to cover smaller more geometrically challenging areas such as planted beds or small strips of grass. Also installed at grade, they accept nozzles that throw from 4 to 18 feet and have radius adjustments from 1 degree to 360 degrees. Pressure regulated and non-pressure regulated units range in heights from 2 inches to 12 inches. However, a 2 or 4 inch head is of no value- insist on a 6 inch minimum height spray head. A typical spray head nozzle consumes between 2 and 6 gallons per minute.
Spray heads are factory designed to operate a 30 psi. However, rotor heads require a minimum of 60 psi. A non-pressure regulated spray head operating above 30 psi waste water! Instead of disseminating the correct size droplet, water is atomized and sent off into the atmosphere. Even though pressure regulated heads cost 25% more they will pay for themselves the first year. Rain Maker only installs pressure regulated spray heads!!! - Hybrid Stream Rotor: This unit incorporated a non pressure regulated spray head with a rotor nozzle. Designed to operate in a 40 to 60 psi range these units allow for us to provide coverage in the in between range where a spray head has too little throw and a rotor head has too much. These units employ nozzles that have a throw range from 13-25 feet. These units also are very efficient and employ flow rates of less than half a gallon per minute per nozzle. Also, when water pressure is too low for traditional rotors (60 psi minimum) these heads can be employed and preclude the need for a pump.
Zone:
(A like group of heads) System design usually calls for multiple zones. You may for example, have a zone that waters the front grass, another that waters a front bed, another that waters a vegetable garden, and one that will fill a pool or water feature. Rain maker constructs zones according to Micro-Climate. This assures that full sun areas and mostly shaded areas receive the proper amount of water.
Fertigation:
Technology from the agriculture industry found a way for us to fertilize every time we water. Results are outstanding. Just fill an in ground tank every few month and the system will take care of the rest
How much does an irrigation system installation cost?
A properly installed quality turn-key system will average, depending on how much hand excavation is involved, $140.00-$175.00 per head.-“Turn-Key Installed” At a minimum this system should include: Installation Permit, Sewer Exemption Meter, 1” Main Line Piping, 1” Reduced Pressure Zone Backflow Prevention Valve, Smart ET based Controller installed by a Professional Electrician, Minimum of 16ga Direct Burial Irrigation Wire, Head to Head coverage with Pressure regulated Spray Heads.
How much water does a system use?
On average each irrigation rotor head uses 2.5-5.0 gallons per minute (gpm). Each spray head averages 1.8-6.0gpm. A typical rotor zone has between 6 and 8 heads per zone and a spray zone has between 8 and 12 heads per zone. Stream Rotors average 1 gallon/minute.
The controller operates the zones based upon daily ET rates. Virtually no watering in April or May. More June, July and August. Then a great reduction mid September until we shut the system off in late October.
How much does water cost?
Each water purveyor (provider) has its own convoluted system in order to try and keep us confused. For the most part they have done a good job, but if we take a closer look it is not an insurmountable task to figure out. Remember Water and Sewer Charges in most all cases are calculated separately – again the importance of the sewer exemption meter!
Annual Maintenance Costs:
Spring Turn on Service
We perform this service in late April/early May. We check the controller for proper programming and signal reception.. We check the system zone by zone for leaks, overall head condition and alignment. We test the Back Flow Valve. Currently Roanoke City and Salem residents are required to have permitting and test results submitted to proper municipal authorities.
$115.50 up to 6 zones. $12.50 each additional zone
$125.00 Backflow Permit and Certification (Salem)
$140.00 Backflow Permit and Certification (Roanoke City)
Fall Winterization Service (system blowout)
We perform this service in late October/early November. This precludes freeze damage. We employ a specially outfitted air compressor that incorporates filtered high volume low pressure air to force the water from the system.
1-3 Zones $85.00
4 to 6 zones $105.00
Next 6 Zones up to 12 $12.50/Zone
More than 12 Zones $10.00 per Zone
Above prices subject to increase based on price of Oil at the time of service
Warranty
We will warranty labor and pipe related products for the period of one year, providing we perform the spring and fall services. Controllers, heads and other parts have varying warranties depending on the manufacturer. We will provide liaison services however; service call charges will incurred.
Now! You know the basics, how do you choose an installer. Keep Reading!!!
Check out your potential installer!
With the ubiquitous world of internet information. You must take the time to do your due diligence. The answers are just a Google search away
- Check the VA Department of Regulation VA DPOR. Here you can check to see if your contractor has proper and up to date licensing. Have a look to see if they are licensed irrigators. Also, check to see if they are Certified Backflow Tradesman.
- Check the BBB Better Business Bureau. This is a great source and now they provide accurate up to date ratings ranked by Grade Letter. It is true they have no regulatory power however, they do report issues and how companies resolve conflicts.
- Are they Certified Irrigation Contractor (CIC)? The Irrigation Association of America assures they have studied and have been tested on proper irrigation installation. It also assures they are completing yearly recurrent education. Most states require this to install irrigation. Unfortunately Virginia does not require this certification yet.
- Are they a good community citizen? While it is not imperative, we at Rain Maker believe it is important to support local causes. We support the local Home Builders Association and give of our time and materials to causes such as “CHIPS”, VA Behavioral Services and support Cave Spring Little League. It is not always about MONEY.
- Word of Mouth. The absolute best info you can get is from someone who has already employed your potential contractor’s services. Do not be afraid to ask. Reference can be helpful, but I prefer to ask the contractor for a customer who had an issue that was resolved.
I hope you will find this information useful! You can see all these products on our web site. Go to rainmakerirrigationinc.com