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: 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.