After you have decided to irrigate your property, the next step is to learn how to effectively distribute water across the landscape. The following walks you through the various aspects of an effective irrigation system, with links and resources found at the bottom of the page. Downloadable tables at the bottom of the page outlining water frequency and amounts needed for different plants are also available at the nursery.
Irrigating efficiently & effectively in the desert
In the dry Upper Colorado Plateau, where precipitation in lower elevations is infrequent and often comes all at once, keeping plants alive is hard. Irrigation is critical to most plants in the landscape in Moab, but how to effectively irrigate in such dry conditions is not straightforward. In the high desert it is most efficient to use drip irrigation to deliver water to everywhere other than a lawn or other dense ground cover, so we refer to drip throughout this explanation.
Very few plants need water daily. Cattails or other wetland plants do, but most plants do best when the the soil dries out between periods of saturation. Many desert plants, such as big sage or palmers penstemon, die when irrigated too much whereas many landscape plants such as daylilies or boxwoods need supplemental water to survive the climate of the Upper Colorado Plateau Desert.
Depending on the scale of your landscape irrigation set up can be rather simple or quite complex. The following guidelines are meant to offer tips, techniques and encouragement for growing plants successfully in a location devoid of soil or rainfall.
Irrigation layout: zoning
Plant layout is a part of efficient irrigation. It is important to set up an irrigation system with zones that deliver water to plants of similar water needs. By grouping plants that have similar water needs it is easier to deliver the right amount of water to the right plants at the right times. Zoning does not mean that all the plants of similar water need must be in the only one part of the landscape, rather it means that they are grouped and linked through a dripline that carries water to those areas.
It is easiest to set up your irrigation zones as you install your landscape. If you are retrofitting an existing irrigation system that is not zoned by water needs but rather by quadrant around the house, it can be tough to properly deliver water to all the plants but with some time and work it can be done.
We suggest the following irrigation zones: a tree line, a medium/high water shrub line, a low water plant line, a groundcover or lawn zone, and a line for annuals and/or vegetables. Having multiple zones based on water needs rather than just on which side of the house the plants are located does use more drip line or other piping, but it allows for more efficient and effective water scheduling and application which leads to healthier plants in the long run.
THE TREE ZONE
The tree line should be set up throughout the entire property to deliver water to just the trees. Establishing an irrigation line to all the trees (or in a large property there may be two of these lines) allows water delivery deeply and infrequently, separately from all other plant needs. This water delivery may also feed other plants from time to time, but its primary purpose is to water the trees.
VEGETABLE GARDENS and ANNUALS
Most annual plants, food producing or not, need water more frequently than other plants in the landscape. In the hottest times of the year these may need water daily, whereas in spring or fall they may need it every few days. It saves a lot of headache to have a dedicated line for these plants.
GROUND COVERS AND LAWNS
Lawns and other ground covers require different irrigation from other areas. These plants typically have shallow but dense rooting structure, meaning irrigation needs to be more frequent than for any other plants in the yard. It is important to deliver water to these plants differently from all other plants in the landscape. Ground covers under trees or around shrubs should still have their own water delivery lines.
LOW WATER PLANT ZONE
Some plants, particularly regionally native ones, really don’t need or want a lot of supplemental water. Plants adapted to the mesas and other upland areas away from water can die with supplemental water. But these plants also can use a boost with supplemental water in years of drought; or if the plants are irrigated carefully they may bloom more frequently or for longer periods.
MEDIUM and HIGH WATER SHRUB ZONES
Medium to high water shrubs and grasses, such as golden currant or boxwoods or golden grove bamboo, should be irrigated together as well. This is not to say these plants can only be located in one area of your property, but it is important that they all be watered similarly. A perimeter planting of these plants may be linked to higher water plants located around a lawn or close to your house. There are some plants, like new mexico privet and three leaf sumac, that have a tolerance for small or large amounts of water. You may want to run two lines to use the least water on these kinds of plants, or lump them with some needing higher watering amounts. You can deliver these two water needs on the same line to a degree by using different drip emitter sizes for different plants (6 gal per hour for high water and one or two 2 gal per hour emitters for those that need a bit less).
OPERATING AN IRRIGATION SYSTEM EFFICIENTLY
Plants don’t need water every day; well, most landscape plants don’t need water every day. Plants like trees and shrubs access water from depths up to 3’, so the soil surface does not need to be wet for the plant to have access to water. Lawns and other ground covers, however, have shallow root systems so these areas need water applied more often. In the hottest parts of the year these areas will need water more frequently than the more deeply rooted plants will.
How often irrigation is delivered is as important as how much water is delivered. Irrigation timing should allow for the soil around the roots to dry between watering cycles, and irrigation should be long enough that it fully saturates the soil profile when water is applied.
DEPTH, OR DURATION: How MUCH to water
Every time supplemental water is provided it should fully saturate the root zone of the plant. For trees that means water needs to reach 2 to 3’ deep; for shrubs, 2’ deep; and for ground covers, 1’ deep (and lawn roots are generally a little shallower than 10”). Getting water to 3’ deep in the soil requires more water be applied when you irrigate.
Different soils will require different run times to achieve saturation to the depths desired. The following table is a guide to understand how much water may be necessary to get water to the entire root zone of the plant. Remember, if your emitter is rated as a 1 gallon emitter, if you only run it for 15 minutes you only apply a quart of water to the plant. An hour of run time will apply one gallon. And the slow application will help the water penetrate more deeply.
Remember to apply water slowly so that it soaks in deeply. Water applied all at once will generally soak in shallowly, whereas water applied slowly over many hours will soak in more deeply. Knowing your soil type is important to understand as well. Sandy soils draw water down quickly – and often will need to be irrigated more frequently that clay soils. Clay soils may require a much slower application of water, even running overhead sprinklers 3 to 4 times in one day to get the water to percolate more deeply. But clay soils also will need to be watered less frequently as they dry out more slowly.
A moisture meter can help to calibrate how long to water – or simply driving a screw driver or other stake into the ground to determine how deep the water has reached.
TIMING, OR FREQUENCY: How OFTEN to water
Each watering zone should be run to meet the needs of the plants in that zone. Remember that trees need water to reach 2 to 3’ deep; shrubs, 2’ deep; and for ground covers, 1’ deep (and lawn roots are generally a little shallower than 10”). It takes longer for the soil at 3’ to dry out than it does for the soil at 10” to dry out. This is reflected in how often irrigation needs to be applied for the best plant health. Plants use less water in the cooler months than in the warmer ones. As the air heats up plants transpire more, meaning water needs to be applied more frequently in the summer than in spring or fall. It is also important in dry winters to supplement water on a warm day once every couple of months. Usually there is enough snowfall in winter that irrigation is unnecessary, but winter irrigation can be important, especially for evergreens that transpire year round.