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Green news from the UC Division of Agriculture and Natural Resources
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Comments:
by Mary N Tran
on May 5, 2015 at 12:45 PM
This article on oaks in the drought is terrific!  
I am currently editor of the PVFA Turnout, a newsletter sent to residents living in the Pioneer Volunteer Fire Protection District, El Dorado County. The article on oaks would be very useful in this area. Can we include your article in our June issue? If so, how do you want to be credited?  
Thanks, Mary
Reply by Pamela Kan-Rice
on May 5, 2015 at 2:46 PM
You are welcome to use the oak article. You can say it first appeared in the UC Agriculture and Natural Resources Green Blog http://ucanr.edu/Green. If you need a name, I’m the one who wrote it.  
 
Thanks for sharing our information with people in El Dorado County!  
Pam
by Robert Meyer
on May 31, 2015 at 1:25 PM
I am on the board of Ojai Trees, a non-profit in the Ojai Valley concerned with preserving the tree canopy here. I would like to use a great deal of your article (crediting you, of course) in an article I would like to submit to our local paper, the Ojai Valley News. May I have your permission?
Reply by Pamela Kan-Rice
on June 1, 2015 at 11:10 AM
You are welcome to use this article as a source for your article for Ojai Valley News.
by Joanne Jackson
on August 7, 2015 at 9:15 PM
My husband and I just bought a neglected 7.25 acres of oak trees in Solano County. We have been cleaning up decades of fallen branches and trees. The larger trunks will be firewood, but the twigs, branches and rotten pieces we would like to put through a wood chipper and use as mulch rather than hauling it to the dump. One of our neighbors has apparently been weed whacking part of our property, so the ground under some of the oak trees is "bare naked" of fallen leaves, etc. Darn near bare dirt. We thought we could used our oak debris as mulch but the article mostly mentions leaves, not twigs, etc.
Reply by Pamela Kan-Rice
on August 18, 2015 at 5:44 PM
From UC Cooperative Extension advisor Steve Swain and specialist Bill Tietje: The short answer to Joanne Jackson's question is that applying the chipped material is fine and will help to conserve soil moisture.  
 
If the homeowner just wants mulch (which is what it sounds like from the email), the chips will do fine going straight from the chipper onto the ground. Adding freshly composted material to the mixture would not hurt, and it might even help to increase desirable microorganisms in the soil and the moisture-holding capacity of the soil. However, it’s not necessary to add commercial mulch to the chipped material. Moreover, because the material the homeowner is considering using came from their own back yard, it is unlikely that any diseases will be transmitted by moving the chipped material. Therefore, the threat of imported diseases is NOT a serious consideration.  
 
Our advice would be to simply chip and apply what they have.
by Linda
on July 11, 2016 at 10:01 AM
Great article! I board horses at a property where we can't do deep watering. The oaks are very stressed, and I've taken a few gallons of water from the tap in our home and lugged it to the barn to water a few of the oaks. I can't obviously do much this way, but the ground is so dry that it soaks in instantly. I figure that a few gallons a week at the base of a tree is better than nothing. Is that true? And, I don't want to cause any rot. Any idea about the best way to do this, and how often? Thank you!
by Lukas Martinelli
on February 1, 2021 at 6:52 PM
Thank you for this informative article! It helped inspire my friends and I to apply mulch to help the drought stressed oak trees on their property in Sequoia National Park.  
 
The foliage has responded well as has the life below ground. We were able to see that the common mycorrhizal network living on the oak roots has been revitalized as a result of the surface decomposition of the wood chips.  
 
It's encouraging to learn that methodical intervention can aid oak woodlands in climate resilience and adaptation.
by Georgette Victor
on June 9, 2021 at 7:42 AM
I have a big problem with a very large and tall Multi trunked Madrone losing an incredible amount of leaves. Should I follow the same instructions?SPTBVV
by Sandra Glover
on April 6, 2022 at 9:47 AM
A city park in Southern California is applying very deep heavy mulch under the canopies of mature coast live oaks. There are 2 layers, the earlier application from 1 year ago which has formed a dense mat that is 3-4inches thick and then a more recent layer that is another 3-4 inches. I’ve pulled the mulch away from the trunk but am concerned about the health of these large trees and have noticed wet cankers on them. Any thoughts?
Reply by Mike Hsu
on April 11, 2022 at 10:04 AM
Hi Sandra, here is a reply from the original blog post author, Steven Swain, UC Cooperative Extension environmental horticulture advisor, Marin & Sonoma counties:  
 
That does seem like a lot of mulch. Oak trees like mulch, but usually their own leaf litter is exactly what they need. Excessive amounts of mulch can and often do lead to the development of cankers, particularly at the tree’s base. In the early stages of canker development, bleeding can occur, as you have described.  
 
A mulch application rate of 3 to 4 inches per year is on the high side, but as long as the mulch breaks down with time, this should be manageable. But the problem is that the rate of mulch decomposition can vary significantly from site to site depending upon environmental conditions. Generally, mulch breaks down best when it’s both warm and slightly moist for extended periods of time. Under relatively ideal landscape conditions, we might expect to see four inches of mulch applied in November break down to less than two inches of mulch by the following June. In less than ideal conditions (e.g., severe drought) it’s possible that the mulch won’t break down much at all. In that case, adding another 3 or 4 inches of mulch may not be appropriate.  
 
Another consideration is exactly where in relation to the tree the mulch is applied. Generally, a thin layer of mulch is fine if it touches the buttress roots / trunk base. But we’d expect that to be one inch or less, as the root flare is generally a key area of oxygen exchange, and mulch application here hinders that. Many arborists/landscape managers prefer to keep the root flare entirely free of mulch, for a distance of up to six inches or so radius from the trunk. For the remainder of areas within the dripline, any mulch layer deeper than about six inches will begin to smother feeder roots, regardless of whether the mulch is close to the trunk or not. Mulching methodology/depth beyond a tree’s dripline is usually dictated by the needs of plants that grow there. The tree has many feeder roots beyond the dripline, but these are generally small and routinely replaced anyway, so exact mulching depths in this region may not matter so much. That said, it’s probably not a good idea to sheet mulch to a depth of 8 inches around a tree’s entire dripline either.  
 
In short: A few inches of mulch is a good thing, but any wisdom taken to extreme becomes folly.
 
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