Taking Care of Our Trees During Drought

All garden trees. even native oaks and sycamores need extra care during continuing drought conditions. Photo by Rosi Dagit

While cloudy skies are welcome harbingers of some rain ahead, the reality is that most of southern California is still suffering from continued drought. Although we have moved out of extreme drought classification to abnormally dry as of October 2017, the trees and chaparral are suffering from the recent heat spells, as well as the lack of rain since last March. Although these plants are adapted to the hot, dry Mediterranean summers, these past six years have taken a toll.

What can you do to help your trees?

Add water, but not too much and not directly on the trunk. Use a soaker hose spread out like a smile on the downslope side of your trees that can cover most of the area under the canopy of the tree. Turn it on around dinner time and let the water slowly seep in overnight. You want to get moisture down to about 3-6 inches under the hose. It is recommended to water once a month from November to March, unless we get some rains to help.

Mulch is magic. Shredded composted tree mulch, or even better the leaves that fall from the tree, should be left on the ground underneath the canopy of the tree.  A layer 3-6 inches works best. Mulch helps retain moisture, moderate soil temperatures and increases the soil biodiversity.

Beware of import mulch. Sadly, the newly arrived “bad beetles,” the polyphagous shot hole borer (SHB) and gold spotted oak borer (GSOB), can thrive in chippings that are larger than one inch. Be sure to check that any mulch you bring on site is from trees that were not infested. We suspect contaminated mulch is responsible for the spread of the SHB throughout Calabasas that is killing many sycamore trees there. Certified mulch is also available by the bag at garden centers.

Minimize Pruning. Now is not the time to do a major pruning. Every green leaf on the tree is providing critical food and energy for the tree, helping it survive the stress of drought and attacks from insects and disease. Removing green leaves puts the tree at a loss for producing energy it needs. Deadwood can be removed at any time, but wait until the rains start and the trees are not as stressed to do any pruning. Then take as little as possible.

Pruning with contaminated tools can spread pathogens that are hard for trees to fight off during drought. Be sure that whoever trims your trees has carefully followed the industry standards for cleaning their chainsaws and pruning saws between trees and sites. If your tree trimmer looks confused when you mention this, find a more educated and skilled trimmer.

Don’t’ move or buy firewood from infested trees. Know where your firewood came from. Buy firewood without bark to make sure that you don’t import any pests to your property. Mark, across from the library, has good stuff available.

Monitor your trees for signs of stress and infestation. Many times, we take our trees for granted and only tend to notice problems when they are well advanced. Take some time to walk around your property and photograph your trees so that you have a baseline to compare their condition over time. Be sure to get the whole tree canopy in the photo and pick your time of day carefully so that the canopy is not backlit. If you see ooze, holes, dark stains or sawdust, take a photo of the problem area with a pen in the image for scale. Check online at www.pshb.org to see if these are normal problems associated with native insects and not a problem, or if they are perhaps due to one of the new problem beetles. If so, contact rdagit@rcdsmm.org for assistance.

Be sure your landscape and tree care crew is up to speed. There are many unscrupulous contractors who are using the invasion of the SHB as an excuse to sell expensive treatments that are not tested or effective and, worse, sometimes downright harmful. To date, there are no approved treatments for SHB. Trunk injections, soil drenches, trunk sprays, etc., all have consequences. Be a careful consumer and check the websites to see if what your contractor is proposing is the current state of care.

The antidote to the loss of so many native trees is to plant more. The bad beetles seem to like larger more mature trees, which buys us some time for baby trees to get established while the researchers find ways to stop these pests.

SAVE THE DATE! Join us on Saturday, January 20, to help reforest lower Topanga State Park. Stay tuned for more details.


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