Tree Care 101: All about Trees
January 27, 2018 8:00am – 12:15pm
Jim Downer is a horticulture specialist with the University of California Cooperative Extension in Ventura County, California. Mr. Downer can be contacted at firstname.lastname@example.org. more info here
Article: Drought, “Water Wise” Gardens and Saving Water in Landscapes.
By James Downer, Horticulture Specialist, University of California Cooperative Extension
Tune up the irrigation system!
Probably the single most important water conserving practice you can do is to maximize the distribution uniformity of your irrigation system. This sounds major but it’s not. It is amazing, but many people never see their irrigation system running because it is on a valve controller, and it runs while they are away or asleep. The first thing to do is to manually turn on the system and see where the water is going. Commercial maintenance contractors should also undertake this procedure, even if it is not within the duties of the job, because irrigation greatly affects everything in the landscape. Seek permission to audit the irrigation system. It is a necessary part of good landscape management. If water is evenly applied where you want it, great! But most of the time this is not the case. There will be plugged emitters, emitters throwing water the wrong direction or onto hard surfaces, breaks in lines, or even lost emitters with water geysers. Just becoming aware of what your water distribution system is doing is critical to saving water. Fix the obvious problems, and you will save water. Further refinement of the irrigation system involves measurement of emitter output, pressures, and distribution uniformity, which is not within the scope of this article. There are many on-line resources that can help get you started on that.
Pay attention to the time of the year!
The most important driving force in plant water use is sunlight. Sunlight (day length) varies following a bell shaped curve over the entire year. The most sunlight occurs in mid-summer and the least in mid-winter. These are the corresponding high and low water using times of the year. Water should be applied with durations that follow the amount of sunlight plants receive. Also, since we are in a climate when most rainfall comes in the winter, there is often little or no need to irrigate after the start of the first rains. An inch of rainfall that occurs in the fall or winter months may give three to four weeks of water supply to a typical landscape. I recommend that you turn off timers (sprinkler valve controllers) in the winter starting in November until the rainfall stops. If we get a sudden warming trend, wind event, or other circumstance that dries the landscape, then irrigate manually to address that issue. You will save a lot of water since you are not automatically watering an already wet landscape.
Water when the plants tell you to!
Plants are the best indicator of drought stress. The most obvious symptom that everyone recognizes is wilt. Physiological wilt occurs when there is not enough water in the plant and the soil to keep the plant turgid. If a plant stays in this condition for long, it may reach the permanent wilting point from which it cannot recover. Before a plant goes into wilt, there are often other signs that it is in drought stress. Also, some plants, like Coast Live Oak, don’t show “wilting” symptoms because their leaves are very sclerified or rigid and can’t actually become flaccid. Before wilting, some plants lose their bright color. Instead of bright green, they may look blue green or grey green. This dulling of color is the first sign of water stress. Some plants, like bamboo and other grasses, will roll their leaves as they dry out to slow water loss. Trees with flexible leaves may show a cupped shape when they begin to dry or may drop their leaves all together (Shammel or Mexican Ash does this). Another indicator of drought stress is reduced growth. This may be ok if plant quality is acceptable because then there is less clipping, but if you notice that plants are not growing as much as you desire or they are not meeting your expectations for general appearance, you may not be watering enough and need to apply more. One of the problems with plants is that although they can tell you symptomatically when they are dry, plants are not very good about telling you when they are wet! Until diseases kill roots or stems, many plants will just grow in wet soils. Sometimes nutrients are not as available in wet soils so some deficiency symptoms may begin to show. Under wet conditions, micronutrients are reduced and become unavailable and macronutrients may leach so yellowing leaves may tell you that soils are too wet. Often however, diseases of root systems occur in wet soils and complicate the diagnosis. If diseases are present, and watering schedules are corrected, the drying soils may stress the diseased plants more and precipitate a rapid decline. Thus it seems that watering appropriately killed the plant. Diseases always complicate this situation.
Understand the “age” of your landscape and the implications on water use!
Newly planted landscapes use a certain amount of water, usually less than what is applied. Often landscapes are overwatered at first to make sure that root balls stay moist as they are trying to root into their new “native” soil. This establishment phase of irrigation should be very short, just a few weeks to a month—then the watering system is adjusted back to a schedule that reflects plant needs, the demands of the climate, and the holding capacity of the soil. This is somewhat of an art. As the landscape grows, irrigation times, emitter placement, and emitter number all begin to (or should) change. More water may be needed in a growing and maturing landscape. The mature landscape water needs should remain constant for any given time of year from year to year (except when we have hot, blowing wind—an anomaly of the weather). The watering schedule should increase and decrease to reflect the increase and decrease of solar radiation throughout the year. Know where you are in this scheme of things, and then consider increasing or decreasing water applications appropriately. Also consider retrofitting your irrigation system to place water where it is needed (farther from tree trunks) and increase the number or type of emitters for larger plants.
Mulch bare soils!
For newly planted landscapes, mulch is an excellent mechanism for saving water. Numerous studies have shown that young plants that are mulched can skip every other irrigation (50% water savings) as compared to unmulched plants. Also, mulches inhibit the germination of annual weeds that will also use water that could be saved in the soil for the intended landscape plants. Be careful where you obtain mulch because urban yardwaste products are often contaminated with noxious weed propagules. Bark or wood chip mulches obtained from tree trimmers are the best mulches for landscapes. They last a long time and are usually not contaminated with noxious weeds. Remember that mulches may hold water, so each irrigation must apply enough water to saturate the mulch and wet the soil beneath to the desired depth. Monitor soil moisture! One of the most disastrous errors of landscape management is not understanding the water content of soils. There are many ways to know if your soil is wet or dry, but few are as good as digging with a shovel and checking the “feel” of the moisture content in the soil. Many landscapes I have inspected were bogs of mud because they were so overwatered. In some cases, water stands all the time in low lying areas. However, in mulched landscapes you may not know how much water is under the mulch. Visual evaluations are very misleading. Probing with a soil tube or even a screwdriver will tell you if the soil is dry. As soils dry they become “tight” and will resist penetration, while wet soils are easily penetrated. Soil moisture
meters can tell you if soils are wet or dry but are not accurate in the middle measurements. Expensive soil moisture monitoring systems, such as tensiometers, capacitance meters, and others, are more accurate throughout the range of moistures in which plants grow, but are also more expensive, may not be portable, and will vary by soil texture and sometimes soil salinity. Digging the soil and feeling it with your hands is one of the best ways to assess soil moisture. It is completely empirical, but rarely are you very wrong about your assessment.
Group plants that use more or less water
One of the most common problems I see is that plants are not grouped according to their water needs. Plants are flexible and will grow on the dry side or the wet side and so most landscapes achieve this odd blend of birches and agaves, but usually one partner or the other suffers. For optimum performance, low-water-using plants should be grouped together as should high-water- using plants. Be sure that turf areas are irrigated by their own irrigation valves. How do we know how much water plants actually use? There is some information on this subject but because studies have been difficult to do for ornamental plants, there is no researched water use information for all the ornamentals we grow in California gardens. We have some data, but very little compared to the thousands of ornamentals that are available for our gardens. The best suggestion I have is to group plants by their climate of origin. Match the climate zones of the plants origin with the microclimates in your yard. There are many resources to find plant origins. Group plants that come from dry or Mediterranean areas together. Stream loving (riparian) plants, or shade, tropical, or other water-loving plants can go together in their own special areas of the landscape. This makes irrigation much easier, more efficient, and the plants ultimately receive the proper amount of water necessary for their growth or maintenance. The biggest advantage is that you or your client will save money on the landscape water budgets and the plants will grow and look better!
Jim Downer is a horticulture specialist with the University of California Cooperative Extension in Ventura County, California. Mr. Downer can be contacted at email@example.com.