Now that summer is here and we have turned our irrigation systems
back on, it is time to monitor the amount of water being used. Landscape plants
suffer more from moisture-related problems than from any other cause. Water
is vital to our plants, but excessive water is often responsible for their decline
and death. When a new landscape is installed, watering frequency and length
of watering times are high in order to get the new plants established, especially
if planted during the summer months. Once the plants are established, the watering
times need to be adjusted to meet the watering needs of each landscape zone.
I have gone back to properties two years after the landscape was installed and
the sprinklers are still programmed to come on every day. Check to see if you
have excessive run-off from your sprinklers – another sign that you may
be using more water than is necessary. Lawns do require water, but if you can’t
walk on your lawn without going “squish-squish” you are probably
over watering.
Feel the soil to estimate the soil moisture. Collect a soil sample representative
of the site with a soil probe or shovel. Roll or squeeze a small sample of soil
into a ball. If the soil will not mold into a ball, it is too dry to supply
adequate moisture to plants. If the ball formed will not crumble when rubbed,
the soil is too wet. If the soil can be molded into a ball, but will crumble
when rubbed, the moisture is probably about right. Sprinkler systems can be
redesigned or heads can be adjusted or changed to improve distribution, plant
performance, and water conservation. Plus, you can save some money on that high
water bill.
Watering around our native oaks can be particularly harmful. Our oaks receive
no summer water in their native environment. Watering within the dripline of
the oak trees during the warm summer months can lead to root disease caused
by oak root fungus. Irrigation for lawns, groundcovers or other ornamental vegetation
should be avoided or, at the very least, kept well away from the trunk. The
idea that young or newly planted oaks can adapt to irrigation is not correct.
Newly planted oaks in an irrigated situation often show signs of decline after
15 to 20 years.
The area within the dripline of a large established oak should be left undisturbed.
The natural leaf litter is the best mulch for oak trees as there is a very unique
micro-climate under oaks that allows them to survive without summer water. The
organic leaf mulch conserves water, provides nutrients as it decays, improves
soil structure, decreases soil pH and reduces soil temperature extremes. There
has been a trend to use river rock under the oak trees to create a dry zone,
but arborists do not recommend the use of these rocks under oaks as they trap
moisture and warm the soil – conditions favorable for fungus to flourish.
And they impede oxygen and gas exchange to the roots.
Decline and early death of our oaks is often a result of inappropriate landscaping
and irrigation practices. Damage usually takes years to become evident, and
by the time the tree shows signs of decline it is too late to correct.
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The Town of Atherton is a community of trees, with a majestic live oak as the Town's symbol.
The Atherton Tree Committee is a volunteer, non-profit, community based organization dedicated
to the preservation of Atherton's heritage trees. The Tree Committee participates in a variety of programs
designed to educate residents about the value of trees in our environment and to encourage appreciation
and protection of our urban forest resources.
Benefits of the Urban Forest
For more information contact Kathy Hughes Anderson at
650.752.0526 or send email to
kanderson@ci.atherton.ca.us
 Tree
Committee Home Page |