GARDENING: A primer on drip & micro-irrigation systems
Free Press Gardening Columnist
I do not like drip systems, especially those placed underneath landscape fabric or a layer of mulch. You can’t see what is happening and you will lose plants before you discover you have a problem. I prefer micro-irrigation systems. To me a drip system consists of a drip line which has emitters inside the hose, or where emitters are installed on the outside of drip tubing. These drippers actually drip unless the pressure is too high. I use micro-irrigation to mean small nozzles that work like the spray nozzles you have on your lawn sprinkler system.
Plants can suffer from too much or too little water when a hidden drip system is used. The dying and stressed shrubs along Riverside Parkway are most likely being watered using this type of system. Or maybe I should say — not being watered properly with this type of system. As you can tell when you drive along this road, maintenance to ensure the system works properly is lacking. The number of staff available to do the required maintenance is obviously less than the number required.
Devices are available for installation at the end of the drip zone that signals when the system is working properly. However, very few people install these notification devices and consequently don’t know when their system is running. Very few people take the time to expose emitters to check the system. Exposing the emitters is quite difficult when they are under landscape fabric. When there is a break in the system or when an emitter is plugged you don’t know you have a problem until the plants start to stress out. Squirrels, mice, and other rodents chew on the plastic parts and cause problems you don’t realize you have until your plants are dead.
I prefer putting a drip system on top of the fabric and mulch layer so it can be seen. I also like to put the drip line so the emitters are up. Drip lines have in-line emitters (inside the tubing) spaced at regular intervals from 4 to 36 inches or more. When you purchase drip line you need to ensure the emitter spacing is correct for the plants you plan on growing. You also need to take into account the mature spread of the plants. When using drip line on trees and shrubs, it should be installed to circle the tree or shrub or laid along both sides of rows of trees or shrubs. As plants grow, you will need to add larger circles or lines of emitters to cover the spreading roots.
Some landscapers use solid drip tubing into which they plug emitters. These are called on-line emitters. They poke a hole in the drip tubing and plug in an emitter. Some of these emitters are referred to as bugs. You can also use quarter-inch spaghetti tubing on the end of which a bug is installed. When the length of the spaghetti tubing is 3 feet or more, the water flow is reduced significantly and the plant does not receive adequate water. If you know the spaghetti tubing is going to be too long, add another length of drip tubing for the inadequately watered plants.
I would rather see people utilize micro-irrigation as opposed to drip irrigation. Micro-irrigation consists of small sprinklers or spray heads at the end of spaghetti tubing. These tiny heads are placed on a plastic stick specifically designed to raise them above the ground. With a special adapter these heads can be used in place of your regular RainBird or Hunter spray nozzles. These mini nozzles are often placed on risers to lift them above shrubbery or flower beds.
Drip tubing is used in many of our local vineyards. The tubing is attached to the lower wire of the vineyard trellis and growers insert on-line emitters as needed on the drip tubing. Other viticulturists plug a length of spaghetti tubing into the drip tubing on the end of which they insert a micro-sprinkler. These emitters hang down from the drip tubing. These systems are still more water efficient than regular sprinklers as they are do not water the ground between the rows of grapes.
Orchards are often watered with drip tubing hung in the trees from which micro-irrigation heads are suspended. Peach trees, however, have a problem with this due to the trunks being wet from the spray of water. Peach (and other stone fruit trees) suffer from a disease called “Gummosis.” This disease is caused by two species of Cytospora, one of which can attack trees through wet intact bark. The other species of this organism attacks stone fruit through bark wounds. Keeping the bark dry is important to helping prevent this disease problem.
To avoid wetting the trunks, it is best to install the drip tubing on the ground and use 180 degree micro-heads placed in such a way they spray away from the trunk. With newly planted trees it is best to water the root ball with a bubbler. But as the tree develops roots beyond the root ball, the emitters need to be changed out to spray nozzles and moved away from the root ball. One emitter per tree or shrub is not sufficient so plan on two or three emitters per plant depending on the estimated spread of roots. As much as possible, tree trunks, especially where the trunk enters the soil, should be kept dry. Mini-nozzles have a knob on the top that allows you to change the distance the water sprays.
While I have not covered everything you need to know about drip and micro-irrigation, the points I have made in the above discussion will get you started on correcting problems you might be experiencing with your drip/micro-irrigation systems.
Dr. Curtis E. Swift is a retired horticulture agent with the Colorado State University Extension. Reach him at Curtis.Swift@alumni.colostate.edu, 970-778-7866 or check out his blog at http://SwiftsGardeningBlog.blogspot.com. He owns Swift Horticultural Consulting and High Altitude Lavender.
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