When some people visit my yard or see photos of my trees, they spot a violation of the rules: Aren’t you supposed to keep mulch away from the trunks of your trees?
(That’s my rule-breaking lime tree in the photo above.)
It’s true, there’s no real benefit to keeping mulch, such as leaves and wood chips, right next to the trunk of a tree. The main reasons to mulch are to prevent weeds, conserve soil moisture, and feed the life in the soil below. Little of that is needed right beside the trunk.
No benefit but some risk
On the other hand, mulch touching the trunk has a potential negative consequence. I’ll let this be stated by the University of California publication, “Fruit Trees: Planting and Care of Young Trees.” It says, “Mulch should be kept several inches away from the trunk to minimize the occurrence of crown rot.”
It’s helpful here to learn more about crown rot. Then we can make sense of why this mulching “rule” can be bent, of why I do bend it.
Crown rot is a disease said to be caused by the Armillaria mellea fungus and especially different kinds of Phytophthora fungi (actually, recently reclassified as oomycetes rather than fungi — but that’s of no practical importance here). The symptoms of the disease can look like drought stress and can show as darkened, even oozing areas at the base of the trunk. (Read more at this UC Integrated Pest Management page, “Phytophthora Root and Crown Rot in the Garden.“)
Why the risk?
But what’s most important is to know why it’s happening.
It so happened that the other day I spoke with Pat Nolan, Plant Pathologist for San Diego County, and this topic was on my mind. So I asked her about the conditions needed for crown rot. Constantly moist, she said.
And so this is the reason for the advice to keep mulch away from trunks: Mulch retains moisture. This is a great thing when it’s conserving moisture in the soil where the tree’s roots are. It’s dangerous when it’s keeping the base of the trunk moist.
It’s all about the watering
When applying mulch, I never deliberately pile it up against the trunk. That’s both wasteful and daring. But neither do I scrape it several inches away from the trunk. Not during application and not later. I just don’t bother.
I can get away with this for two reasons.
One, I don’t water my trees right at the base of the trunk — except during the first month for newly planted citrus or avocados. I apply water out near the edge of the tree’s canopy. So the trunks of my trees stay generally dry because of this.
Two, I water as infrequently as possible. Remember, as Pat Nolan said, it’s constant moisture that is required, not just any moisture at any one time. (Obviously! All trees get wet trunks during a heavy rain.) This is crucial because I use sprinklers and sometimes they get knocked and end up spraying the trunk for one or more irrigations.
Lamb avocado tree with micro-sprinkler that has a deflective wedge aimed at trunk in order to keep trunk dry — dryish at least.
No big deal. As long as the irrigations are far enough apart such that the soil at the base of the trunk has dried out in between, Phytophthora won’t find the environment hospitable.
If you use drip emitters on your trees, then make sure they are at least a foot away from the trunk — again, except for the first month or so after a new tree is planted.
Take away
So what’s the answer? Should we keep mulch away from tree trunks? Sure. But don’t stress about it. The stress should be more on watering trees as infrequently as possible and watering them where they prefer to grow their roots, which is away from their trunks.
You might also like to read my posts:
For the first time ever (like 10+ years) I composted and mulched (composted green waste and compost blend) my citrus this winter and all of them took off this spring like I’ve never seen before. Huge green growth spurt (as in almost double in height and 50% wider) in the case of my lemons and limes) and exponential bloom production, so much so that they are totally crowding each other. I wish that I’d planted them farther apart than they are. Anyhhoo…compost and true mulch are amazing!!! What took me so long?!
Thanks for clarifying the distance from trunk issue. This makes complete sense.
Makes sense. I can get so caught up in the details and caveats. If our trees are organic, so should we be about the rules. Thanks for easing my rule-following mind.
so glad I found this site, i’m devouring all your info… thank you for all our knowledge and effort in spreading it
Hi Greg, I see this “rule” most often broken… especially at my home. I’ve noticed when I pull mulch back from the trunk of fruit trees, Argentine ants come scattering out… never good news. So I’ll fill area with water to discourage the ants.
1. How do I treat white Fungus on my avocado tree?
2. How do I deal with cracks in my avocado tree trunk
Hi Robert,
Have a look at this post: https://gregalder.com/yardposts/white-powder-on-avocado-branches/
Hi Greg,
I’m a bit confused as to mulching.
I understand from above that mulching is good.
However in the winter, it’s recommended to not have anything on the soil under the plant as the earth can emit warmth.
If the mulch is removed, won’t the avocado plant’s roots that grow up through the mulch be laid bare to the cold?
Do you mulch year round even in winter? Ie. The mulch is never removed. And will the mulch in winter hold too much water?
I’m in a SF Bay Area zone 9 near Stanford U. I’ve just put in an avocado sapling. The plant is 3 years old but it’s only the second month in the ground. So far it’s doing well. Fingers crossed.
Best regards,
-Elaine.
Hi Elaine,
All good questions. I leave my mulch in place year-round, including in the winter. I’ve experimented with removing mulch from under young trees in the winter but haven’t seen an obvious difference in the cold damage sustained so I’m not yet convinced that removing it is worthwhile. I’m going to experiment with it more this winter though.
Young avocado trees don’t usually have any (or at least not many) surface roots yet, but for older trees, removing the mulch would certainly mean exposing many roots.
I’ve never experienced or seen a problem where mulch retains too much water. Mulch like compost or wood chips is coarse compared to soil and so it has a lot of air within it. Even if it is fully saturated, it remains well aerated too.
For your newly planted tree in your area, I would just be ready with something to protect it on nights that are predicted to get below freezing. See this post if you haven’t already: https://gregalder.com/yardposts/protecting-avocado-trees-from-cold/
Awesome, thank you!
Our Hass avocado tree has many roots that are at the surface. We currently have a messy lawn planted under the 18-year-old tree. I would like to remove that messy (weedy) lawn and replace it with something that requires little maintenance. I have asked at nurseries and have not really received a response. We live in Fontana (Santa Ana wind zone). Our very large tree produces well. Any ideas?
This website is fantastic. I’m binging your content as I plant a bunch of new fruit trees in Lakeside. Thank you!!!!!
Thanks, Jessica! Lakeside is so near to me in Ramona and has very similar growing conditions.
Hi Greg. I’m thinking of removing soil in the front yard and laying paver over there. I think of putting these soil under my avocado tree canopy (10-feet diameter). I guess it’ll be at least one foot high. Are there any problems with that for the tree and landscaping-wise?
Hi EP,
Don’t do that. Trees in general don’t like this, but avocados especially don’t because their roots need a lot of oxygen so they like to form roots near the soil surface. Adding a bunch of dirt on top of them will likely suffocate them.
By the way, you can add a foot of wood chips under an avocado tree because the wood chips are far less dense than dirt; the wood chips are full of air spaces.
Great! Thanks Greg so much for your fast reply. Have a great day!
Hello Greg.
Do U have any experience with growing Fuyu Persimmon tree in southern California?
I have one about 4-5 years old, in a sunny spot, loaded with green good size fruits now, but the upper young delicate leaves of the canopy got brown burnt like spot on the edge., almost like sunburn..
how much watering do they need? maybe I over watered them? ( twice a week,10 min each, drip system .)
with the water restrictions we have here (LA), I wonder if they need more or less than what they get?
U give such a clear down to earth explanation with good photos. !
Thanks!!!
Hi Esther,
My guess is that the tree is not getting enough water. Up the water, but don’t be dismayed if you don’t see an improvement in the tree’s appearance at this point in the year. It’s no longer in a growth phase. You’re just aiming to not cause further stress at this point.
Hi Greg, I recently had a tree trimming co. deliver a free load of wood chips to my property in San Clemente. I have about 35 fruit trees including 23 Avocado trees. I applied the wood chips around 1 of my avocado tree & it became druppy & brown tip leaf about a week later & before it was looking good? So now I’m worried about applying the wood chips to the rest of the orchard. The wood chips are hardwoods from south orange county areas as I requested. Any thoughts on what may be going on?
Hi Peter,
One possibility is that you applied a layer that was thick and fresh enough to compost, and therefore it was “cooking” the roots near the soil surface.
If so, it was a temporary problem and will go away once the wood chips cool although the leaves have been permanently damaged and only new leaves will be undamaged.
In the future, you can either add a thinner layer of fresh chips (less than four inches is thin enough) or wait a couple weeks before applying a thicker layer.