Looking for the lowdown on tree rings

Often we use our blog space as a soapbox from which to pontificate, but today I’m looking for some input from our loyal readers.  Last week I received a note from an editor looking for some words about tree rings.  We’re talking about landscape tree rings for planting annuals or perennials, not dendrochronology.


The editor was interested in specifics on tree rings for large existing trees such as what type of materials to use, what types of flowers or plants worked best, which trees can or can’t have tree rings, etc.  My reply was short, maybe even a little curt, “I don’t have any experience with tree rings but our general recommendation is to avoid grade changes around trees whenever possible. After I sent the reply I started thinking, is there any real harm to tree rings?  I’ve seen some that looked pretty nice (seen many that look like crap, too).  For most trees the amount of surface area covered is small compared to total surface root area.  If care is taken not to bury the root collar and trunk, would the tree notice covering a little bit of mostly structural roots?   Would appreciate thoughts (pro and con) from those with direct experience.

15 thoughts on “Looking for the lowdown on tree rings”

  1. I don’t know much about how tree rings are installed, but here are some general thoughts: It’s true you would have to be careful not to bury the root collar and trunk, as keeping them exposed to the air is key for a tree’s long-term survivability. The rule of thumb for adding mulch around a tree is to put in between 2 and 4 inches of mulch; it stands to reason that the tree would prefer (if someone does install at tree ring) that the depth of soil added inside the ring be no greater than four inches — it’s my understanding that roots themselves need the oxygen most available in the topmost soil horizon — so I’d think that more than 4″ of soil added could be iffy. The ring itself would have to be a surface-sitting material — that is, you wouldn’t want to dig down to put a base course of stone or masonry units below grade, because that would likely lead to a number of cut roots, and as a result, trunk injury. (Root trauma often is reflected in trunk health; when you see injury down low on a trunk, and it has not been caused by mechanical damage, you may be able to trace it to some sort of root trauma.) Rings with soil depth deeper than 4″, and/or with soil that covers the root flare, will likely stress the tree — the tree in the first photo looks like one on which you might expect to start seeing signs of stress…The diameter of the ring would likely be a factor, too — the rings shown in the photos are relatively small which, as you say, Jeff, makes for a relatively small surface area covered. Going wider would cover up the small feeder roots with additional soil….

    I have seen tree rings, or timber walls, added around street tree pits, and they’re never a good idea. The treepit is usually where a street tree’s roots has greatest access to moisture and oxygen, and if you pile more soil in there and then underplant you create great conditions for the underplantings, at the tree’s expense. I remember one spring seeing a tiny treepit outside a Cambridge hai
    r salon that had been raised and planted with annuals; petunias and celosia and alyssum spilled over the edges, and morning glories climbed strings up into the tree. It looked like a great way for the salon to announce its beautifying presence on the street. While the annuals thrived through the growing season, though, the tree looked sadder and sadder. It had been stressed to begin with (it was a street tree, and had to struggle in any event), and by fall it was dead, which kind of ruined the overall effect….

    Hmm. I probably would try to avoid tree rings where possible.

  2. I, myself, am not a huge fan of “Tree Rings”, especially those that are gaudy, or improperly installed.
    Although, I will put this out there, because he speaks words that only I can only wish to say! I highly reccomend reading The Renegade Gardner’s [http://www.renegadegardener.com/] amazing and hilarious article [Design > The Astonishing Truth Behind Tree Circles
    ] to which I put up a quote:
    “As my research progressed and the patterns emerged, I was left with only one possible conclusion: the heinous tree circles we witness in yards across America are unquestionably being created by beings from other planets.

    It’s one of my favorite reads of his many hilarious articles.
    If we can ge
    t a guest post from Don on The Garden Professors, I will be a happy camper!

  3. I am not a fan. It does nothing to enhance the appearance of the tree, and more often than not, results in the root flare being covered and choked by several inches of dyed red “cedar” mulch. The only instance in which a ring would be beneficial would be if it were simply a safety perimeter, putting several inches between the lawn and the trunk. This helps reduce lawn mower and trimmer injuries, which as we know, can be fatal.

  4. I’m with Cynthia – I’ve utilized very basic tree rings in the lawn part of the landscape to keep people from butchering the bark. Mulch around the tree, grass edged regularly during the growing season – no other interface. Mostly it works. I would concur with not changing the grade – it spells ruination! My only other experience is in a play area where kids love to dig at the soil around some old firs. I’ve used old windfall branches to create a very informal (yet still nice) ‘ring’ around the tree that functions as an inexpensive way to create a visual barrier to deter foot traffic and digging in the root zone.

  5. I concur with Donna B, the Renegade Gardener’s take on tree circles (tree rings) has the best take. I hate snobbishness, but Don has pretty much turned me nearly into an anti-tree circle snob . . .

    If mulch volcanos are a bane, how are tree circles (rings) better?

  6. My favorite tree rings still bring a smile to my face. I lived in an old apartment complex in Blacksburg and it had some nice mature trees. The sugar maple right outside my front door had a mulch ring about 15′ in diameter and each year it was planted with Impatiens. It looked like they bought a flat of each color and planted all of one flat before starting the next. The result was concentric rings in orange, hot pink, lavender, white, red, etc. It was spectacularly awful…like a hairless dog 🙂 Thanks for the memories!

  7. Boy I wasn’t the only one who thought about the Renegade Gardener’s delightful article.
    In my yard we try to remove grass to the drip lines of our trees and then mulch with just enough to replace the amount of sod we removed. Having a good number of trees we do not do this treatment to every tree annually. I have some then planted with a groundcover or some type of non invasive perennial depending on the tree species.
    Too many trees I see with a ring of about 6″ removed and the inevitable mulch volcano (*shudder*). Its rare that I see a tree circle that loos good.

  8. I have always thought this would be a great topic for research. In my travels, I found very little effect on matures trees. But with smaller trees, all that can go wrong does. Even when planted at the soil level of the new ring, the roots will act like a large contaner, hitting the edges and start to circle. They don’t grow down under the ring. I have one resident who buried 3 crimson king Norway maples 30 years ago, all three survived, but all 3 are dwarfed, and look at the closely, all are in horrible shape.

  9. Bob, that’s an excellent observation. It makes sense that trees with structural roots outside the ring would do fine, while younger trees might have difficulty passing the barrier.
    Bert – sounds like a great long term demo project!

  10. The tree ring discussion has moved on, but I wanted to share what I think might be an extreme example: a pink chestnut (horse chestnut? buckeye?) in our backyard, completely surrounded by a section of cement (sewer?) pipe. I’ve put up a photo here: http://www.flickr.com/photos/revalani/5611647732/

    Several neighbors have similar cement rounds in their yards, remnants, I’m guessing, of some public works project in the 1950s, when these houses were built.

    Our ring is cracked in a couple of places, and the tree roots have grown down and out into the rest of the yard. The tree appears healthy, so I don’t think we have a root-circling problem.

    I called an arborist when we bought the house to see if we should be concerned; his attitude was that the tree was probably a little bonsai-ed, in that it would never reach its true potential, but that overall it was healthy and not stressed.

    But it sure is bizarre — and yet another example of how difficult it is to visualize how large a tree will get in 50 or 60 years.

  11. Reva, thanks for the link! It’s…unique. What more can I say? Back then people thought tree roots looked like carrots.

  12. I have been using metal tree rings to keep mulch from building up over time on the shoulders. I put the rings at soil grade to prevent the unsettled mulch from coming over and building up what looks like original grade over the shoulders. I do this at planting when creating a new bed. When trees get underplanted and the area mulched over time, this levelling commonly happens and it can’t be readily seen.
    My question is how far out from shoulders should ring and then mulch start?

    1. There isn’t any evidence that mulch over the root “shoulders’ causes any harm (and by mulch, I mean arborist wood chips, not bark or compost or any other mulch that can cause harm). And in fact, it’s not natural for trees to be bare shouldered – their root zones are covered in mulch that builds naturally. So I would advise removing the ring and just allowing the mulch to move naturally.

      (If you aren’t using arborist chips, I strongly advise you replace whatever you are using with them. They are superior to all other mulches in terms of tree and soil health).

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