When to Mulch Trees

The best time to mulch a tree is:10 Years Ago.  The second best time is:Right Now!



In order for any tree to make the transition from a maturing tree to an old tree, organic matter (mulch) must be in place, ideally it will have been in place since the tree sent out roots.


The functions of mulch with respect to trees are:

1. Water retention.  This is easily observable in the landscape especially in a drought year like we had in 2023.  Trees that had an adequate amount of mulch in place prior to spring showed significantly less stress in their crowns than trees that did not have mulch in place.
2. Protection from hot/cold temperature extremes.  The mulch acts as insulation against the hottest hot and coldest cold snaps that have been happening with greater frequency.
3. Increased availability of nutrients for use by the tree(s).  As mulch breaks down, the organisms doing the work- mycorrhizal fungi- trade water and micro-nutrients to the trees roots in exchange for carbohydrates.  This relationship is symbiotic and the Trees (above ground portion) can be described as a byproduct or expression of this underground symphony.  Trees have co-evolved with the mycorrhizal net over millennia to capture sunlight, store it under ground, and have their parts recycled for the next generation.  Left alone the forest (nature) diversifies and makes itself richer and more resilient.

So when we mulch our trees we are making a choice to align ourselves with Natural Law.  The new term we are seeing is “biomimicry”.  This does a good job of describing what we try to do in our yards.  A ½ acre of grass is basically a desert from a biodiversity standpoint (we do have a lawn to play in at our home).  For a huge organism like a White Oak planted in the yard, there is no resupply of nutrients taking place and the primary functions of the tree- Grow, Reproduce, Defend, Stabilize- will suffer.  The plight of the tree is exacerbated by the use of chemical fertilizers and poison’s like herbicide.   As the tree gets older, it will start to draw on its reserves more and more-eventually starting to decline much sooner than its forest dwelling brethren.  A 100 year old tree in the Urban environment is becoming rare.  


Does this mean that we ought to be covering our entire yards with wood chips?  Not necessarily (although that would be a HUGE ecological benefit to your corner of the world), but are there areas that we are mowing that we could let go wild?  There always are, we simply need to reframe our perspective on what beauty is (I’m talking to the dandelion haters here).  If you want to support trees that are in the middle of your yard, you can start by establishing a mulch ring a minimum of 2x the diameter of the trunk (4x diameter would be exceptional) that is 8-10” thick upon first application.  Keep in mind that the mulch is going to degrade to about 2-4” thick within a calendar year and will need to be reapplied.  The other 6-8” of mulch will have transformed into an ⅛” thick layer of black gold compost.


Anecdotally, when the deforestation of our Eastern Woods commenced in the 1700-1800s there was reported to be 3 FEET of this composted topsoil over the now remaining red clay (subsoil).  If all the dead tree parts that it took to make 3 FEET of topsoil were piled up, we would be swimming in 192 Vertical Feet of wood chips.  WOW.




Arborist love,
Jason