Periodic drought is a way of life for those living in southern California – this means not only the people, but the plants and animals as well. Fortunately, most trees – even those hailing from faraway lands – can survive the long, dry summer with a little extra water.
Home Sweet Home
Most of the plants and trees native to Los Angeles, Santa Monica, Beverly Hills and the rest of the region have developed physiological mechanisms or physical characteristics that enable them to cope with these regular dry spells. Even those that tend to grow in riparian areas or in low-lying grounds must develop some ways of surviving waterless periods, as particularly dry periods may turn creek beds into little more than sunbaked mud.
But these adaptations are hardly infallible. While the healthiest individuals often survive extended droughts, many trees battling pests or growing in sub-standard locations struggle to survive prolonged dry spells. Fortunately, many of these trees can be saved with a little supplemental irrigation.
Exotic Introductions
In stark contrast to native plants and trees, which have adapted to the region’s Mediterranean climate, many ornamentals and trees that homeowners install hail from regions with more rain. For these plants and trees, supplemental watering is often necessary for any reasonable chance of emerging from the drought unscathed.
Recognizing the Signs of Water Stress
Whether your trees are native to southern California, or they are native to some lush rainforest, you’ll need to keep an eye out for the signs of water stress. Some of the most common and important signs include:
- Leaf Lightening
- Crown Dieback
- Premature Leaf Drop
- Browning Leaf Edges
- Wilting
For further reading on the subject, check out this great PDF from the City of Santa Monica Urban Forest Division.
Providing Water Appropriately
Having decided that your trees are in need of some extra water, it is important to provide it to them in the most efficient manner possible. This not only ensures your trees will derive the maximum benefit from the water, but it will also help you avoid wasting any water in the process.
It is important to water trees in a much different manner than you would water grass and other shallow-rooted plants. You want to saturate the upper 16 to 24 inches of the soil, which means that you’ll need to apply water very slowly and over a long period of time (hours). This will encourage the tree roots to penetrate more deeply into the soil, while frequent, light water applications will encourage the proliferation of shallow roots. By encouraging the development of deep roots, your trees will be better able to access moisture from deep in the soil, thereby giving them an even better chance of emerging from a rainless summer unscathed.
A basic guideline for watering calls for 10 gallons of water for every inch of the trunk diameter at breast height (about 4.5 feet above ground), up to a maximum of 160 gallons. You can do this with a hose, but it is perhaps easier and more efficient to provide water via a water bag or drip-irrigation system. Most drought-resistant species can survive the summer with only two water applications per month, although species with more moderate water needs may require 3 or 4 applications per month.
Note that these guidelines are for established trees. Newly installed trees require more supplemental water than those who’ve already established deep and robust root systems. New trees typically require about 10 to 20 gallons of water, administered on a weekly basis.
Don’t Be Afraid to Ask for Help
With a little research and hard work, many homeowners will be able to support their trees through the summer. However, it is often advisable for homeowners to solicit professional assistance – particularly if your trees are battling disease, pests or other stressors.
If your trees are struggling with the lack of rain, give your friends at Evergreen Arborist Consultants a call. We’d be delighted to help you care for your trees and give them the best chance for a long life.