Intelligent and dedicated water management is vital for tree health, growth, flowering and fruit development.
Provide water for your trees with love and attention as you would for other living things under your care, children, pets. Don't "set it and forget it", manage it! Watch for signs of water deficit, dry cracking soil, wilting foliage, discoloration, decline and die-back.
Water a wide area not just near the tree trunk, water the entire area of the absorbing root zone which spreads as far as the foliar canopy and more. Yes, more than the 'dripline'. Figure 1.5 to 2 times the radius of the dripline to be safe, and to encourage a wide and deep root zone.
Water deeply to wet the soil a minimum of six - eight inches, preferably to 10 - 12 inches.
Check this two to four hours after watering, or the next day, by digging down in a couple of spots to see how deep the water infiltrated.
Mulch the soil surface to help retain soil moisture and maintain soil organic matter content.
Even native trees and drought tolerant trees, especially those with altered, unnatural environments, can benefit from a once-a-month deep watering.
Drip irrigation systems can keep trees alive, but are usually not enough water for trees to thrive. Drip is often inadequate and creates drought stress, unless installed and maintained to provide deep watering.
Upgrade to Netafim type "smart drip", that has soaker-hose type function with more complete coverage of the soil surface and soil volume in the root zone.
Frequent shallow watering (multiple times a week), can cause root rot in susceptible trees. Infrequent deep watering is preferred (once a week for water loving trees and once a month for drought tolerant trees). Lawn watering is too much, too frequent for trees and is incompatible for most tree plantings. Few species can tolerate years of turf watering, definitely not native oaks; problems occur even after 10 -20 years.
All About "Watering Deeply"
From 'The Spruce'. Written by Marie Iannotti
“Every gardener has heard the term "water deeply," meaning that it is better to water deeply once a week than to water superficially more often. What does it mean to water deeply, and how can you tell if you've accomplished it?
There is no hard-and-fast definition for watering deeply, but it generally means that the water is able to soak at least eight inches below the soil surface. The point behind this is that most plant's roots are not sitting close to the soil surface. They have worked their way down into the soil, in search of water and nutrients. This helps protect the plant in times of drought because the soil surface will dry out much quicker than it will below ground, where the soil is cooler. Since you cannot control the rain, there will be weeks when your garden will get much more water than it needs and weeks when it will be your responsibility to see that your garden is watered.
Another common gardening recommendation is to make sure your plants get at least one inch of water every week. One inch does not sound like a lot, and it isn't. That's a minimum. It is better for the plants if the soil gets a good soaking down to at least the eight inches mentioned above. That's because one inch of water will evaporate or dissipate quickly, whereas a thorough soaking several inches below the soil surface will linger long enough for your plant's roots to get a good drink.
You could try to get around this by giving your plants a little bit of water daily, rather than a good weekly soaking. If you have a drip irrigation system where you are guaranteed that the garden really will get a daily watering, that's fine. However, it is not a practical plan if you are watering by can or hose. Plants that are used to getting frequent water will not develop the deep root system that is needed for the plant to survive periods of drought, so making your plants dependent on daily watering and then missing a few days will cause long-term problems. Once a plant is water-stressed, it can take weeks to recover, and in the case of annuals and vegetables, every week counts.
How to Test How Much Water Your Garden is Getting
How quickly water runs through the soil and how much is absorbed for the roots to access will depend on what type of soil you have, the weather conditions, and how fast the water is being applied.
Water runs through sand much more quickly than it penetrates clay. That's why it is advised you amend both types of soil with organic matter, which is great at holding onto the water just long enough for the plants to get at it. A three-to-four-inch layer of mulch will help conserve whatever moisture is there.
However, there's a simple test to get an approximate idea of how much water is falling on your garden. Water your garden by whatever method you have and then wait a half an hour. At that time, dig down into the soil with a trowel. If it's not wet eight inches or more below the surface, it might be that you haven't watered enough or it could be that you watered too fast and the water ran off elsewhere. It is probably both.
Next time, try a gentler stream of water for a longer period of time. A gentle soak for an hour or two is better than puddling soil around your plants and moving on. It primes the soil to absorb more water and to allow the water to spread out in the soil.
It can take a few tries to get it right, and you don't have to be obsessive about getting exactly eight inches. The point is to make sure the soil is absorbing and holding the water long enough to hydrate the plants. Once you master the concept of watering deeply, your plants will stay healthier in whatever weather comes their way.”
You can water deeply with an existing irrigation system programed appropriately, or on "manual" setting, for customizing the time cycle. Or you can use a hose-end sprinkler. Move it around and position to get full root zone coverage. Soaker hoses linked together and serpentined throughout the root zone is another option.
Water the soil surface as far as the tree foliar canopy spread, and more.
Avoid setting sprinklers or drip irrigation emitters close to the tree or shrub stems, causing the trunk and root crown to stay wet and incur crown rot.
With sprinkler, you can measure amount of water with a rain gauge. Shoot for one inch to start with as a minimum.
After watering, or no later than the next morning, dig down and see how far the moisture penetrated into the soil profile. I use a soil sampling tube, but a shovel works too. Six to eight inches is a minimum for the trees, 10 to 12 inches depth is better.
As a tree health care specialist in the San Francisco-Monterey region, one of the most common problems that I get called for, is decline in health and die-back of native oaks. Frequently the problems turn out to be related to inappropriate watering. The following information is consistent with my experience, and important for homeowners and landscape professionals to understand and practice.
(The following is an excerpt from Compatible Plants Under And Around Oaks, a publication of the California Oak Foundation. )
CALIFORNIA NATIVE OAKS AND SUMMER WATER
"Oak roots, like those of most trees, are extremely sensitive to environmental change (soil compaction, altered soil grade, increased moisture, paving, etc.). These changes reduce the soil oxygen, impair root function and create conditions more favorable to root pathogens (disease organisms).
Once established, native oaks seldom require supplemental irrigation to survive. Still, most oaks, especially those in urban settings, will benefit from one to several deep waterings during the hot, dry summer when drought stress is greatest. However, when the frequency of irrigation exceeds a monthly application, root health and function are likely to suffer.
Frequent irrigation displaces much of the oxygen in the soil, producing unfavorable growing conditions for oaks. This can lead to reduced growth and vitality, increased susceptibility to insect and disease pests, die-back and decline. Oak roots, particularly those originating at the base of the tree (root crown), are quite vulnerable to root pathogens. Although normally inactive in dry soil, common root pathogens proliferate under warm, moist conditions created when water is frequently applied to the soil during the summer. Root diseases are more severe when soil drainage is restricted as in heavy clay soil, hardpan, and in low areas.
Frequent summer irrigation near the root crown is likely to cause root decay which, over time, will destroy the roots, kill the tree or cause structural failure. Disease prevention and management involves changing or maintaining environmental conditions to favor tree growth, while discouraging root diseases. This involves the reduction of plant stress through judicious watering, appropriate landscaping and proper tree care.
Avoiding irrigation for lawns and water-loving ornamental vegetation under native oaks helps ensure their health. Contrary to conventional wisdom, young oaks do not adapt to frequent irrigation. Although oaks in turf or irrigation settings often appear healthy, most become increasingly susceptible to root disease with age. Soil conditions also play a role in disease development. Oaks planted in fast draining soil may survive frequent irrigation for many years.
Newly planted oaks do require frequent and regular irrigation until they are established, usually two to three years. This fact is often overlooked by people who assume that because oaks are drought tolerant, they don’t need supplemental watering."