Advice from the Help Desk of the
UC Master Gardener Program of Contra Costa
Help Desk Client: My mature 40 foot redwood trees seem to be showing signs of stress from the continuing drought. While it gets just as much water from my garden irrigation as it did pre-drought, I now am noticing that various branches are showing needle die-back. Can you tell me what's wrong? Is it the drought or something else affecting the tree? And if it's something else, what is it and what should I be doing to correct it and bring back the trees to full health?
We have completed our research. The symptoms are consistent with the types of water stress we are seeing on redwoods in the central parts of the county where redwoods are not well-adapted. Under the microscope, there also appeared to be some fungus, but not the aggressive type that would cause a serious problem in your trees. More likely the fungus, in an opportunistic way, came into the needles that were already dying from the drought stress. No treatment is advised or necessary, other than good cultural care of the trees.
The best course of action is to follow the advice you received while visiting us last week: making sure that you water the trees out at the dripline and beyond during the warm, dry summer and fall months prior to the rainy season. Avoid watering near the trunk which can predispose the trees to rot. Redwood trees will compete with each other if planted closer that 7 feet apart, increasing their water needs. Water stressed trees should not be fertilized. As long as the needles are green and growing during the spring and summer, fertilizer is probably not needed.
Also, as noted above, during the drought, the MGCC Help Desk has fielded many questions and concerns about redwood trees. A previous blog responded to many of your and others' concerns, especially with advice on irrigation, at http://ccmg.ucanr.edu/HortCoCo/?blogpost=19256&blogasset=12496. Your perusal of the advice and recommendations should help you determine the necessary steps to make your redwood trees healthy again.
I hope that your trees will become healthier ithis spring after all this good rain we are having along with the possibility of supplemental irrigation over the non-rain periods. Please let us know if you have any more questions.
Help Desk of the UC Master Gardener Program of Contra Costa County (JL)
Note: The UC Master Gardeners Program of Contra Costa's Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. We can also be reached via telephone: (925) 646-6586, email: firstname.lastname@example.org, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog (http://ucanr.edu/blogs/CCMGBlog/).
From the Help Desk of the Master Gardeners of Contra Costa County
Client's Questions and Requests: (Originally from a phone call to the MGCC Help Desk...) I'm a new resident of central Contra Costa County having bought a house in Walnut Creek. The house and garden are probably 30-40 plus years old and mostly mature. There is a grove of 30-40 foot Redwood trees that look like they are doing o.k. and many other mature garden plants. We intend to do some remodeling on the house and garden which will include some new planting, but the redwood trees will remain in place for privacy and shade. In our replanting of parts of the garden we would like to utilize drought tolerant plants. We also have a creek adjacent to our property that we wish to protect with minimal disturbance. Do you have some guidance for us to consider as we rethink our garden.
As we discussed previously, We'd be reluctant to recommend planting redwood trees in central or east CCC (and with some reservations in west CCC). However, with your existing mature trees, the goal is to maintain their health and promote longevity. The links provided below provide information for redwood tree care and irrigation. You mentioned that the trees are very large and that they appear to be in good condition, so it is likely that after four years of drought they have been getting water from somewhere - maybe the nearby creek provides a high water table. However, even if we get rain this winter, drought conditions are likely to continue, and you may want to plan for future irrigation.
Although some mature trees can often survive one season with only one or two deep waterings during the spring and summer, several years without enough water can result in severe drought stress and even death. Drought-stressed trees can also be more prone to damage from diseases and insects as well as the effects of increased salts in the soil from lack of ample irrigation. Salts in the soil may also increase depending on the salinity of the irrigation water provided (such as may be the case with recycled water).
Here are some great articles about redwood cultivation in California that you may find helpful in deciding how to best approach improving and/or maintaining tree health:
The article in the link below addresses a new technique (TRIC) by UC horticulturists designed to water landscape trees by the home owner maximizing the use of water and insuring that water is reaching the drip line of the tree: http://ccuh.ucdavis.edu/public/drought/tree-ring-irrigation-contraption-tric-1/tree-ring-irrigation-contraption-tric. While TRIC system provides an effective optimal and automated solution, if the cost appears prohibitive, UC has now designed a simpler solution for less cost, but it requires more home owner attention and management (see RSIC).
You also asked about finding an arborist to inspect the health of your trees - the International Society of Arboriculture has a web tool to assist you in finding qualified members (i.e.,Certified Arborists) in your area: http://www.treesaregood.org/findanarborist/arboristsearch.aspx. You may want to consider a consulting arborist first as well as friends or neighbors for recommendations.
Finally, here is the link to the UC Davis Arboretum's list of good drought resistant plants for our area: http://arboretum.ucdavis.edu/arboretum_all_stars.aspx. We also have a lot more information on this subject should you need it.
Thank you for contacting Master Gardeners. I hope you will enjoy your new home, and if you have further questions please feel free to contact us again.
Help Desk of the Master Gardeners of Contra Costa County
Note: The UC Master Gardeners of Contra Costa's Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. We can also be reached via telephone: (925) 646-6586, email: email@example.com, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog./span>