In our June 2021 newsletter, we discussed how to water your mature trees in a drought. This month we continue that discussion by sharing with you the water-saving benefits of mulching around your tree.  
What is Mulch?
Mulch is a layer of material applied to the surface of the soil. There are a variety of mulches that are used for this purpose; it can be chips produced by tree companies, gravel or cobblestones, composted material to immediately enrich the soil, plastic sheeting to suppress weeds, or a variety of products you can buy in bags at your local home improvement store. 
The Benefits of Mulching for Trees 
Mulching is great because it:

  • Reduces the amount of water needed in your yard by 10-25%
  • Decomposes and releases nutrients into the soil           
  • Reduces soil compaction so roots can breathe           
  • Maintains soil temperature and protects roots from cold and heat           
  • Discourages grass and weeds―which compete for nutrients―from growing near the tree trunk            

What kind of Mulch Should I use for My Trees?
Of course, we believe wood chips, produced by tree services such as ourselves, are best! The mixture of wood and leaf material creates a wonderful beneficial product for your tree and it is FREE!
What about other kinds of mulch?
Gorilla Hair is the trademark name for a product created from chipping redwood and cedar bark which turns it into a stringy hair-like product, hence its name. It has characteristics that make it very popular with landscapers: it is consistent in appearance, clings to steep slopes, and doesn’t decompose as quickly as tree chips. However, we do not recommend Gorilla Hair as a mulch around trees. Because it decomposes so slowly it doesn’t improve the soil and, in our experience, it tends to collect water and not allow it to reach the soil surface and beyond, thus not helping to conserve water around trees.
Cobblestones are another popular “mulch.” Even though it is not organic and does not decompose, it does help prevent weeds and sort of helps to retain water, but only if the tree or surrounding landscape completely shades the cobblestones. If placed in direct sunlight, the cobblestones will heat up and bake the tree roots. Because of this, we do not recommend this type of mulch for trees in sunny areas.
The same can be said for weed mats or plastic sheeting. They are good for suppressing weeds but add nothing to the soil and can hamper watering. Not what you want during a drought!
How Much Mulch Should I Apply? 
When you’re mulching around trees, a 2-4″ layer is best. Any thicker and future rain will have a harder time penetrating down to the soil. There is also the possibility of smothering the roots. Roots need oxygen to breathe and if the mulch is too thick, the roots may grow into the mulch base searching for air. You also want to keep the mulch away from the trunk of the tree. Make sure there is at least a 3-5″ wide mulch-free ring around the base of the tree. You do not want to bury the trunk with either mulch or soil as you can create an environment for decay fungus to thrive. We also recommend you deep soak your tree before you apply a layer of mulch. And, if you are using a soaker hose or laser tubing to water your mature tree (as suggested in our last newsletter), it is best to put it under the mulch. 
However, if you are spreading mulch on an empty lot with no trees and lots of weeds, then thicker is better. A thick layer of mulch will keep the sunlight from germinating weed seeds. 
I have been told to avoid eucalyptus wood chips
Contrary to public opinion, there is absolutely nothing wrong with using eucalyptus for mulch around trees. All wood eventually rots and becomes part of the soil. The only way eucalyptus could kill plants is if you work the fresh woods chips into the soil as an amendment. Wood chips need nitrogen to decompose and if you work them into the soil before they have fully decomposed, they will pull nitrogen out of the soil and cause the plants to yellow. This is not just with eucalyptus chips, but will happen if you use any kind of fresh wood chips. One positive attribute of eucalyptus chips is that they are weed-free! However, because of this, eucalyptus chips can affect the seeds of plants you want to grow. So it is not recommended to use eucalyptus mulch around annuals or vegetables. But around trees, it’s fine.
Free Wood Chips – what to expect
The biggest complaint about using free wood chips is its appearance. The load is either not consistent enough or people complain there are too many leaves. Living in California where every yard is full of evergreen trees and shrubs, it is difficult to create leaf-free wood chips. Theoretically, if you get chips in January and February after the deciduous trees have lost their leaves, the chips should have fewer leaves. However, the only way to achieve leaf-free chips is to remove a dead tree. In fact, the picture to the right shows chips from a nearby dead pine. But there is a potential drawback to these chips. As you can see, compared to my shoe at the bottom, the chips are really big. That’s what happens when you chip good-sized logs (12″-20″) as compared to chipping smaller diameter (2″-10″) branches. However, even though the chips are bigger than usual, they are perfectly fine to spread around your trees and help retain water just like the smaller chips.
If You Want Perfect Looking Chips – You Can Buy Them
If a uniform and formal look are important to you, then there are places where you can buy mulch that has been processed to achieve that consistent look. EcoMulch, located in Martinez, takes wood chips from local tree companies and re-processes them to create a uniform-looking product. You can visit their website at and see what they have to offer.
If you would like a truckload of free wood chips from Traverso Tree Service, we are happy to provide them for you. Simply CLICK HERE to submit a request online to be added to our chip list or call our office at (925) 930-7901 and ask to be put on our “Chip List.” Our office staff is also happy to answer any questions you may have about mulching the root zone of your trees.