Understanding Proper Irrigation

By: David Bates 

After planning, prepping, and planting those new landscape beds, now its time to kick back and enjoy them, right? Enjoy yes, but fully kick back, no.   It is essential that these young plants receive the correct amount of water. A plant can only absorb water that is within its root zone. New plants, understandably, have small root zones. Until they have had a chance to spread their roots, which will take at least two weeks, check the moisture at and around the base of the plants. Most plants will need water every other day for the first two weeks. If it rains, do not assume everything received enough water. Check to see if the ground is moist around the plants.  Annuals may need watering daily throughout the summer months, depending on location and type of plant.  Before you begin to water, it is best to have a complete idea of just what needs to occur during the irrigation process.  Many people have a poor understanding of just how to approach this vital task.

 

Methods of Watering:

There are many ways to water, from a hand held hose to automatic irrigation. New plants are not anchored into the soil yet, so water them gently no matter what method you use. Also, to prevent leaf molds, mildews, and fungi avoid watering the foliage if at all possible. Always water deeply. The soil should be moist to at least a 4" depth. If the bed is on a slope avoid water run off and erosion problems by watering a little bit at a time, moving the irrigation around until everything has received four inches of water.

 

The ideal time to water is early in the morning before the temperatures rise. This way you will not lose much water to evaporation and, as the day warms, water that fell on the foliage will be evaporated reducing the risk of fungal diseases. The worst time to water is in the middle of the day, especially when using over-head watering (sprinklers). Too much water is evaporated and the water on the foliage can cause scalding during the heat of the day. Evening watering is common because it is the most convenient time to water. The main problem with watering in the evening is that the water on the foliage of the plants does not have time to evaporate create prime conditions for fungal problems.

 

Handheld:

When using a hand held hose to water be sure to attach a nozzle or watering wand to the end of the hose that dispenses the water in rain shower style (Fig. 1). Do not use a mist nozzle or a power nozzle (Fig. 2). A mist nozzle will take a very long time to apply enough water to the soil and it will wet the foliage increasing the risk of fungal disease. Plus, a large amount of the water will evaporate in mid-air. So save your water bill and your plants. A power nozzle can cause immediate damage. It is anything but gentle, and will blast the plants' roots and splash soil everywhere.

 

Soaker Hoses:

Soaker hoses are wonderful things! They can be snaked among the plants in the bed, just under the mulch. Soaker hoses take a little longer to water, but you can just turn them on and leave them. Because they are on the ground there is virtually no evaporation. The water is applied directly to the soil so there is little risk of foliar fungal problems. You can use soaker hoses anytime during the day, but the best time is still in the morning.

 

Oscillating Sprinklers:

Oscillating sprinklers are usually used to irrigate lawn areas rather than bedding areas. Because this is a type of overhead watering all risks mentioned before apply. Therefore, be sure to water early in the morning.

 

Automatic Irrigation:

There are many types of automatic irrigation. A system can have overhead sprinklers (with spray heads and/or rotary heads), and bubblers or drip lines at ground level.

Today’s sprinkler systems include sprinkler heads of two types: spray heads and rotary heads. The types of heads utilized on a specific project will be determined by the dimensions of the area being covered, the water pressure available for operation, and a variety of other factors.

 

 Spray Heads

 

These are the most common visual when thinking of a sprinkler system.  These heads are placed around the lawn and planting beds. 

 

Spacing can vary widely, based on the specific head used, but they rarely exceed 15 feet. (more about nozzle sizing below).  Spray heads normally retract below the soil or bed to allow for mowing and other uses while watering is not taking place.

 

Spray head bodies are commonly available in various sizes, the difference being the height that the spray apparatus or nozzle is lifted above the body of the head. The pop-up heights vary between manufacturers with 2", 3", 4", 6", and 12" pop up sprays being the most commonly available. The high-pop-up models including the 6 inch and 12 inch are used for flower and shrubbery bed areas where risers might be unsightly or subject to damage from passerby.

The most basic version of a spray head is a fixed (non-pop-up) head mounted on a riser. Risers are sometimes PVC, sometimes copper, with the spray nozzle on top. Risers are used to keep the nozzle above the level of the projected growth of shrubs or groundcovers to ensure even distribution of water. These fixed heads typically have nozzles that are interchangeable with the pop-up units used in lawn areas.
 

Rotary Heads

These sprinklers are larger devices that are used in open, un-interrupted spaces that allow water to be dispersed 25 to 30 feet or more. These heads typically pop-up during use and retract after operation for use in lawns or other areas with foot traffic. They are also available in fixed (non-pop-up) versions for use on risers in large planting areas. There are two basic types of rotary sprinklers, categorized by the mechanism that causes the sprinkler to rotate. These types are impact rotors and gear-driven rotors.

Impact rotors are the oldest type of rotary heads. Originally developed for use in watering agricultural crops in the 1930’s, impact rotors have been used since the 1940’s for turf irrigation.

The basic operation of an impact sprinkler is simple. As water leaves the sprinkler nozzle it comes in contact with a spring-loaded drive arm. This arm is shoved aside by the force of the water. The spring then returns the arm to its original position and it again comes into contact with the water and also a stop or shoulder on the sprinkler body. The impact against the shoulder causes the entire head assembly (and sprinkler stream) to rotate slightly. This constant impact and movement will cause the head to rotate a complete circle and slowly water the entire area within that circle. In addition, each time the water makes contact with the sprinkler arm, a small amount of "splash" is created that falls near the sprinkler head.

For part-circle sprinklers, an attachment is added to this assembly to reverse the rotation and cause the head to move backwards before it completes a full circle of revolution. This back and forth rotation allows the head to be used in areas like corners and along walks or streets.

Many industry representatives argue that the impact rotor provides the most uniform coverage of any sprinkler on the market, including spray sprinklers.

However, the impact sprinkler’s popularity has waned due to some significant operating drawbacks. The largest problem with impact sprinklers is their high maintenance requirement. As an impact sprinkler is activated, it rises out of its assembly to approximately 4 inches above the turf. During the time the sprinkler is in operation, this open cavity in the sprinkler case becomes an open catch all for trash, mud, clippings, insects, and all types of yard debris.

This debris is washed into the mechanism during the normal operation of the head. Periodic maintenance is required to keep sprinkler canisters clean and to keep dirt and debris from causing damage to the mechanism.

The design of an impact sprinkler also has many exposed, moving parts. The springs that control the motion of the arm and the reversing mechanism can bend, rust, fall off or get entangled with debris.

Gear-driven rotary sprinklers are used in most modern systems. With these sprinklers, water turns a small turbine (water wheel or fan) in the base of the unit which drives a series of gears that cause the head to rotate. The gear drive mechanism is sealed from dirt and debris and operates without the irritating clatter of impact sprinklers. The gear driven design has dominated rotary sprinkler sales in the irrigation industry for some time, in both residential and commercial sites.

Gear driven rotors represent the biggest improvement in irrigation technology since the invention of PVC pipe. They are easy to adjust and are factory sealed to keep contaminants out. However, as with any type of equipment, the gear driven rotor can be mis-used and mis-applied.

Although the individual gear drive rotor unit is several times more costly than a spray head, its wider spacing capabilities means fewer heads are needed to cover a given area.

Some installers will use these heads in spaces that are too small for efficient rotor operation. These installers attempt to reduce the number of heads and piping connections, thus reducing trenching and labor costs. When a rotary sprinkler is forced to cover an area too small for its intended design, the result is increased misting and inefficient coverage (See Misting below). If a rotor is adjusted to reduce its throw more than 25% of its factory specification, it is being misused.

Sprinkler Nozzles

The nozzle is the device that water passes through as it is leaving the head and is to be dispersed onto the landscape. Irrigators rely on different nozzles to vary the quantity of water dispersed during the watering cycle, as well as the distance that water is to be thrown by each head. The amount of water distributed over a given area per minute can be doubled or tripled by choosing the correct nozzle.

Spray nozzles come in varying sizes and patterns, depending upon the manufacturer. If selected and installed properly, they form a spray pattern that will provide a uniform application of water over a given area. Years of research is behind every new nozzle before it is released into the marketplace.

Rotary nozzles usually are inserted into the body of the head after it has been installed. Available nozzle sizes vary with each manufacturer. Uniform and complete coverage depends on selection of an appropriate nozzle for the area to be covered. Two different nozzles will cause the same rotary head to vary the distance of throw by 10 feet or more and increase water use by factors of two or three.

Misting is caused by high pressure at the sprinkler nozzle that results in the breakup of the spray into a very fine atomized mist. It often appears as a fog over a system as it sprays. The presence of misting is an indication that adjustments may be necessary to increase water droplet size as the spray leaves the head. Discuss this problem with your irrigation contractor to improve the overall efficiency of a system that is experiencing spray drift or misting.
 

Clogged nozzles cause improper application of water and reduced efficiency by misdirecting the spray pattern. "Spitting", partial spray patterns, or a complete lack of water being discharged by a sprinkler head can be caused by debris caught inside the assembly. Removal of this debris must be done carefully since most heads are made of plastic. Digging or gouging at the orifice or opening can cause permanent damage and permanent changes to the spray pattern.