Mulch Volcano or Mulch Donut? How to Mulch Around a Tree
Drive through almost any neighborhood around here and you'll see it: a tree sitting in a tall cone of mulch piled right up the trunk. It looks neat, and whoever built it meant well. It's also one of the most common ways a healthy tree gets hurt without anybody noticing.
Fall is a good time to top off mulch. It holds moisture and keeps the soil temperature steadier through winter, which helps anything you planted this season. So before the new mulch goes down, here's how to put it where it actually helps.
What's Wrong With a Mulch Volcano
The problem is where the mulch touches the tree.
Bark on a trunk is meant to stay dry. Pile mulch against it and it stays damp, softens and opens the door to decay, disease and insects. A volcano also buries the root flare, the spot at the base where the trunk widens out into the main roots. Under all that mulch, roots can start circling the trunk and slowly choke it, and you won't see it happening.
A deep pile also keeps the top of the soil wet all the time, so roots stay shallow instead of growing down. Shallow roots are the first to suffer in a North Texas August.
Most volcanoes aren't built in a day. They grow a few inches a year, with fresh mulch going on top of last year's without anyone checking what's already there.
How to Build a Mulch Donut
The fix is simple. Picture a donut instead of a cone: a wide, flat ring of mulch with an open spot in the middle where the trunk is.
Keep it 2 to 3 inches deep.
That's enough to hold moisture and keep weeds down. More than that can keep roots too wet in our clay.
Spread it wide.
On an established tree, go out at least 3 feet from the trunk. On a young tree, take it out toward the edge of the canopy if you have room.
Pull it back from the trunk.
Leave a few inches of bare ground all the way around so the base of the tree can dry out.
Leave the trunk flare showing.
You should be able to see the trunk widen out where it meets the ground. If your tree goes into the ground straight like a fence post, the flare is probably buried.
Fixing a Volcano You Already Have
You don't have to start over. Rake the extra mulch away from the trunk and spread it out into the wider ring. Go easy near the base so you don't scrape the bark.
Once it's cleared, look for the flare. If you find roots wrapping around the trunk, or the flare is buried under soil and not just mulch, have someone look at it before it gets worse.
This comes up a lot in older yards. Plenty of Lake Dallas front yards were planted in the early 2000s, and a tree that went in with the house can have years of mulch stacked at its base. If the rest of the bed has aged out too, our post on fixing a 20-year-old landscape covers what to keep and what to replace.
Going forward, check the depth before you add more. If last year's mulch is still a couple of inches deep, rake it to loosen it up and you're done for the year.
Want Us to Handle It?
Our landscape and planting crew can refresh your beds, pull back volcanoes and mulch new plantings the right way. If you're putting anything new in the ground this fall, read our fall planting guide first. Get a quote and we'll come take a look.
Rob Dilts
Owner
RD Services
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