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Tuesday, November 11, 2014

How To Keep Trees Healthy All Season Long

By Julie Saare-Edmonds, California Department of Water Resources

It’s been long, dry year for California. Although we have had touches of rain here and there, the long-term weather forecasts don’t look too promising. Add that to a couple of previous dry years and the results are dry soils all over the state.

Trees growing in nature depend exclusively on rain and snow and many of our larger urban forest trees do, too. Because our rain and snow have been far less than average, the moisture stored in soil is now depleted and the consequences are stressed trees in danger of dying or becoming susceptible to pests and diseases.

Our urban forests are valuable resources because of the benefits they provide, from clean air to shade and homes for wildlife, and increased property values to food and healthy communities. If trees are affected by drought, we must act to keep them healthy.

Trees growing in lawns may be dry and under stress, too.  Because so many Californians have taken saving water to heart and cut back on lawn watering, they unintentionally put their trees at risk. Lawn sprinklers will keep a tree alive but it’s not the best way to grow healthy tree roots, and once you cut back watering, shallow rooted lawn trees have a hard time coping with less water.

We’ve gathered some ideas to help you create a strategy to keeping the most valuable plants alive with limited water. The key to saving water while saving your trees is to decide which plants are the most important and dedicate the limited water to them first. Because trees are decades-long investments, they should get first priority. Next important are shrubs and perennials and lastly include lawn and annual flowers.

Reducing lawn watering will make your lawn less attractive, but that is only temporary; losing a beautiful tree that was planted 25 or 50 years earlier would be a tragedy.  But there is something we can do about it!

The first thing to do is check the appearance of the tree. At first glance, drought stress damage and fall leaf drop may look similar but there are subtle differences. Brown crispy edges on leaves or visible wilting are both signs of drought stress. Dieback of branches also indicates damage from drought. Trees undergoing normal fall leaf drop will show even color changes and the leaves should still have softness to them until they fall.

Next, check the soil moisture level using a small shovel or a large screwdriver. If the screwdriver can’t be pushed in, or the shovel pulls up dry and crumbly soils, then the tree needs water. You may be tempted to turn on the lawn sprinklers, but there is a better way to get moisture to the tree roots. (Important to note: if a tree is less than 5 years old, it will still have quite a few roots near the trunk, but with older established trees the roots will have grown outwards to capture as much rain as possible).

The drip line, which marks the edge of the tree canopy, is a good place to start watering. To “deep water” the tree, lay a soaker hose in a ring around the tree just inside the drip line and continue in a spiral outward. Let the hose run until the water soaks in to a depth of about 8-12 inches, but watch for runoff, especially on clay or compacted soils. Depending on soil type and flow rate of the hose, this may take a few minutes to a few hours. Check the soil to make sure you’re not watering too deep or too little. To prevent runoff you may want to install a simple battery operated or wind-up timer to shut off the hose after a certain amount of time. If water runs off before water soaks in, turn the water off and turn it on again after a couple of hours of soak-in time. If the tree you are watering is small, start laying the soaker hose closer to the trunk or hand water.

If this upcoming winter has long dry spells, check the soil once or twice a month and water trees when necessary. Dormant (bare) trees need moisture to keep the roots alive and it is especially important to keep the soils moist for broadleaf evergreen and needleleaf evergreen trees that grow year round.

As part of your plan to keep your trees healthy, check with your local water supplier about the days of the week you are allowed to water your landscape. As the seasons change, watering days may change. Remove grass and weeds around the trunk and add mulch such as shredded leaves or wood chips for the added benefit of keeping lawn mowers and string trimmers away from the tree. Fine compost can also be applied to the grass surrounding the tree to give it and the grass some natural fertilizer.

If you have questions about your trees call the local Cooperative Extension Master Gardeners or your local urban forest/ tree foundation.

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