Determining the best irrigation schedule for a mixture of landscape plants is difficult enough but when salinity is involved, either in the soil or in the irrigation water, it complicates matters. Let’s cover some irrigation do’s and don’ts and see how salinity might affect the way we irrigate. Avoid Daily Irrigations Except for shallow rooted plants like lawns, annual flowers and vegetables in raised beds, daily irrigations should be avoided any time of the year. Many turfgrasses and annuals have root systems that extend into the soil 12 inches or less. During the heat of the summer and under desert conditions some of these plants may require daily irrigations. The deeper you should water. Lawns, annual flowers and annual vegetables have the shallowest roots and need to be watered the most often. The concept of irrigating nondesert landscape plants is focused on wetting the root system to its entire depth, allowing the soil to drain and re-wetting the soil again when half of this water has been used by the plant or evaporated. The Amount of Water Applied Varies with the Size of the Plant So we can see that the volume of water applied in a single application is directly related to the depth of the root systems of plants. When designing a landscape irrigation system we try, to the best of our abilities, to put plants with similar rooting depths on the same valve or station. Create irrigation zones in your landscape that reflect the needs of the plants in it. This is because the only way to water less or more often is to turn the valve to that irrigation line on or off. This is done with the valves. So each valve should represent different irrigation depths in your landscape; trees and large shrubs, smaller and medium size shrubs and small plants. Other valves could include annual plants and lawn and desert adapted plants which don’t need to be watered as often. You could even create another zone just for cacti. (This diagram originally appeared in Sunset magazine many years ago demonstrating Hydra zoning or mini oasis landscaping) More often than not we are handed an irrigation system with a mixture of plants that have a variety of rooting depths. When deciding an irrigation schedule for a single valve or station we generally have two options; set the number of minutes based on the average rooting depth of all the plants or let the plants with deepest root systems dictate the number of minutes of station runtime. Do We Conserve Water or Minimize Plant Problems? This decision depends on whether to conserve water or minimize landscape problems. When we decide to under irrigate some plants so the majority receive the correct amount of water, we may see some plant damage. If the under irrigation is not severe, we may see the slowing of plant growth, a decline in density due to leaf drop, leaf tip or burning of leaf margins. When plants are severely under irrigated then we begin to see branch die back and in some cases death. This is a mixture of a mulberry tree with cactus growing underneath it. Water the mulberry tree and the cactus gets over irrigated. Water only for the cactus, as this was done, and the mulberry doesn’t get enough water. Under irrigating, or applying less water than dictated by a plants rooting depth, can also impact safety issues. What happens if we under-irrigate large trees such as pines which have shallow roots to take up water but require deeper roots to anchor it in the soil? Current irrigation technology is based upon time management and varying how water is applied to plants. This technology varies the amount of water applied to plants by changing the number of minutes valves are open, increasing or decreasing the points of water emission or changing the rate of water applied at the point of emission. This translates to increasing or decreasing the number of drip emitters, bubblers, nozzles or spray heads or substituting old points of emission for new ones that have different rates of application. This is a highly sophisticated Hunter ACC irrigation clock. These types of irrigation clocks are expensive but give you a tremendous amount of flexibility. They wouldn’t be good for small landscapes but an excellent choice for large landscapes that have a lot of irrigation variability. Making these changes to an irrigation system that was designed by a professional and focused on the uniform application of water, more than likely will make the system less uniform and less efficient. This will likely result in substantially higher water usage. These types of alterations to professionally designed systems must be done with care. These six station inexpensive irrigation controllers are fine for most small landscapes that don’t require a lot of flexibility. When to Make Changes in the Irrigation System? There are some obvious cases where changes must be made. For example, changes must be made when some plants are receiving excessive amounts of water or not enough water while others on the same valve appear to be watered adequately. As plants get bigger, they need more water. When plants get bigger, their tops get bigger as well as their root system. Increasing plant size requires the application of higher volumes of water. Increased plant size dictates that the area irrigated under the plant also needs to be increased. Logic tells us we need to increase the amount of water by applying it to a larger area. Just because a few plants on an irrigation valve have grown larger seldom requires increasing the number of minutes of runtime. Other plants on the same circuit that received adequate amounts of water would then be over-irrigated for the sake of a few. Is Increasing the Number of Minutes the Right Decision? Of course increasing the number of minutes is the easiest solution to the problem but is it the right one? The quick fix of bumping up the number of