Beware of Mulch Volcanoes

They might be killing your trees

I’m obsessed with mulch volcanoes. These are the dark brown or red or black piles of mulch you see mounded up against the bases of trees in the landscape.

I spot them everywhere when I’m driving. I pulled over to take the photo above, for example. And once I see them, I can’t unsee them.

You might have created mulch volcanoes at your house, thinking you’re helping your trees. That’s understandable. It does seem like a good idea. Like if some mulch is good, more must be better.

In fact, adding a mulch circle around a tree can be very beneficial if done properly. It prevents lawn mowers and weed whackers from getting close enough to a tree to damage its bark and roots, and more.

But too much mulch can cause trees a lot of harm, even death. And the sad thing is that landscape professionals sometimes get this wrong.

To be honest, I’m pretty sure I used to do this myself before becoming enlightened by an arborist friend. Before I became a no-mulch-volcano evangelist.

During the pandemic, I completed Master Gardener training. For my final project, I created a no-mulch-volcano infographic. I gave an impassioned presentation about it to my fellow gardeners.

I’ll put the infographic below, which explains the problems caused by mulch volcanoes and best practices.

Please note, if you have an existing mulch volcano around a mature tree, it’s worth consulting with a certified arborist about the best way to remove it. This can be tricky if the mulch has broken down into soil, and tree roots have grown into it.

Otherwise, if you can gently rake away any mulch touching your trees, leaving flat circles no more than 3” deep, please do.

My new hori hori knife

Here’s something I’ve resisted for a long time—using a garden knife. Even when my friend Julie told me about the Japanese version years ago, I wasn’t interested. Which was unusual for me, because I’m deeply inspired by Japan, its landscapes and gardens, rural Japanese life, Japanese design, and so forth.

But as a “landscaper,” I learned to use full-length tools for efficiency of movement. I loved having a minimalist set-up, with a small pruner as my only hand tool.

Over the past year, I’ve become interested in no-dig methods of gardening, and I appreciate the rationale behind minimal soil disturbance. So instead of pulling weeds, lifting them with a garden fork, or digging them out, I’ve learned cutting them just beneath the soil line is a better way to go.

My Nikasu NJP650 Original Hori Hori Namibagata Japanese Stainless Steel Weeding Knife arrived from Amazon. Ray and Aoife (husband and daughter) both made comments upon seeing it on the kitchen table, because it does look scary! It’s extremely sharp, much more so than I expected.

The knife has a straight edge, a serrated edge, and a wooden handle. Compared with other hori hori knives I saw online, this one has the most basic design. The blade is stainless steel, and the sheath is leather. It seems sturdy and well-made.

I tried cutting out some dandelions in my front garden. The hori hori knife worked beautifully. I’m sold. I still need to learn how to sharpen this tool. Thoughts welcome.

A few good small landscape trees

Cercis canadensis (Eastern Redbud)

Friends invited me over yesterday to discuss their landscape. The inciting incident was the recent removal of trees.

One, an old crabapple, had provided a nice separation from the neighbor’s side yard as well as a pleasant view from the kitchen window. My friends wish to replace it as soon as possible and were looking for suggestions.

The site has average soil, southern sun with shade from the neighbor’s house at times, and a nearby driveway (and therefore possible salt runoff from car tires in the winter). We live in USDA Plant Hardiness Zone 5a.

Here are my top five choices for the new tree (including a new smaller crabapple cultivar, since the old one had been healthy but just grew too large), all of which will remain less than 30’ tall and wide:

• Syringa reticulata (Japanese Tree Lilac)

  Full sun tree. Hardy to zone 3a (the lower the number, the colder it will become in winter). Salt-tolerant. Tolerates most soils. Deer-resistant once established.

• Betula nigra (River Birch)

  Full sun tree. Hardy to zone 3b. Salt-tolerant. Tolerates acid to neutral soils. Can grow larger than 30’—look for a small cultivar if needed. Deer-resistant once established.

• Crataegus virdis ‘Winter King’ (Winter King Hawthorne)

  Full sun tree. Hardy to zone 5a. Salt-tolerant. Tolerates most soils.

• Cercis canadensis (Eastern Redbud)

  Full sun or part shade tree. Hardy to zone 5b (three are thriving across the street from my house here in zone 5a). Tolerates most soils.

• Malus spp. (Flowering Crabapple)

  Full sun tree. Hardy to zone 4b. Salt-tolerant. Tolerates most soils. Can choose a more compact cultivar than was previously planted at my friends’ house.

I’m going to suggest they take this list as well as a photo of their site to our largest regional nursery and talk to the staff there about their needs. Especially since the nursery could deliver and plant the tree for them and will offer a warranty for one year.

I’m also going to suggest they meet with our village’s tree commission expert, a retired forester. He’ll have good ideas about deer protection needs and more.

Last, it could be a great idea to plant two of the new trees, rather than just one, locating the second further down into the backyard where there is plenty of room. From a design perspective, it would add to a sense of unity in the landscape.

Mystery plant identified

Remember the giant plants that sprung up in my mini meadow? Beth, the community garden manager, tracked down Chloe, the person who gardened in my raised bed last year.

Chloe tells us it’s Korean perilla leaf, or “Kkaennip” (Korean name). Perilla frutescens is its botanical name.

Chloe was thrilled to hear the perilla leaf had reseeded, and she’s coming over to harvest the bounty. She said in an email, “It’s delicious as wraps for Korean barbecue, chopped up with noodles, pickled, etc., and you can eat the seeds, too, and make oil from them.”

Who knew? Let me know if you’ve grown or cooked with this plant!