Don’t Mulch Too Much

August 1, 2011 | By | Comments (16)

Volcano

Ken Schmidt calls them “mulch volcanoes.” And while they don’t spew molten lava or stand thousands of feet tall (like Mount Hood, above), they definitely spell bad news for trees in the landscape.

A landscape architect with the prestigious landscape architecture firm of Mahan Rykiel Associates in Baltimore, Ken bemoans the widespread practice of piling up ever-growing “volcanoes” of mulch around trees. Instead of helping trees grow, overdoing the mulch does just the opposite.

Mulchy See, Mulchy Do

Why do so many people pile up mulch around trees every year without thinking? It’s a copycat crime. Nothing is more persuasive than seeing your neighbor do something with confidence. It’s even worse when you see a landscape contractor do it.

“Right now, I’m looking out my window across the street at a willow oak that has 8 inches of mulch piled against the trunk for no reason,” he says. “It sends the wrong message to the community, because they think it’s the right way to do it.”

The Right Way to Mulch

Mulching with organic matter – whether it’s shredded hardwood bark, shredded cypress, ground pine bark, or pine straw – can be a boon to trees. It keeps down weeds (preventing damage to trunks from lawn mowers and trimmers), cools roots, and helps the soil retain moisture. Plus, as mulch slowly decomposes, it adds organic matter to the soil, enriching it.

Grumpy recommends planting a tree so that the top of the root ball is ½ to 1 inch above the soil surface. When the loosened soil settles in the hole, the top will be about even with the soil surface. (Planting too deeply, so that the top of the ball is below the soil surface, is a big no-no.) Then cover the ball with a layer of mulch 2 to 3 inches thick. No more. Depending on the size of the tree, the diameter of the mulched area around the tree could range from around 3 to 6 feet. Mulch should not come in contact with the trunk.

Good example 2A properly mulched tree lets air and water reach the roots, while keeping down weeds.

The Wrong Way to Mulch

Many people mulch too deeply. They either apply way too much to begin with or pile new mulch atop last year’s mulch that hasn’t fully decomposed. So instead of the desired 2 to 3-inch layer, the layer grows to 6 inches, 8 inches, and even 10 inches deep.

Bad mulching example 3Here’s a typical “mulch volcano.” Notice the mulch piled up against the tree trunk.

What harm does deep mulch do? Let Grumpy count the ways.

 

1. Roots need oxygen in order to work.  Burying them deeply under mulch decreases the oxygen supply.

 

2. Lack of oxygen prevents beneficial soil microbes from breaking down the mulch. Instead, harmful soil microbes produce substances that are toxic to roots.

 

3. Trees surrounded by mulch volcanoes may send shallow roots into the mulch, instead of the soil. This makes them more susceptible to drought, stress, and wind.

 

4. Piling up mulch against the trunk provides a safe haven for chewing voles and harmful insects and can promote rot due to excess moisture retained by the mulch.

 

Can We Talk?

While we’re on the subject of bad mulching, here are some other heinous practices you should avoid at all cost.

 

1. Using red-dyed mulch (below). As Ken notes, “The color draws your attention to the mulch instead of the plantings.”  Think of it this way. How many of you have a bright orange toilet in your master bedroom, so it’s the first thing that folks look at when they enter? (Although to be fair, orange would help at night.)

Red mulchNotice how the circle of red mulch draws attention away from this stunning fire hydrant.

 

2. Using black-dyed mulch. Black absorbs heat in summer. So instead of cooling the roots, your mulch does the opposite.

 

3. Using shredded rubber mulch. Yep, it’s recycled. But do you really want your yard smelling like a NASCAR track on a hot summer day?

 

4. Using lava rock mulch. Where do you think you live? On the slopes of Krakatoa? Now that’s what I call a mulch volcano!

 

—-

Thanx to giveawayguy for the cool fire hydrant shot and Mahan Rykiel for the mulching pix.

 

COMMENTS

  1. Carol Harris

    I am desperate to get information about best practices for mature Leland cypresses. We have 12 mature. Just bought out home and they are not doing the best they could. I need to know how to winterize them best. Should I add compost throughout the understory? Should I add mulch spread out throughout the understory? Can browned needle limbs be removed in November ? I’m in zone 6b. And lastly when it says to water deeply is thus full open hose and how long under each tree. I simply must save these trees and I’m desperate for info. Pleaee help. I’ve read online and books and need situation specific info. Thanks in advance. Best regards Carol Harris Shenandoah County Virginia October 31 2016

    October 31, 2016 at 10:20 pm
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  3. Speaking of leafing out…

    […] around the trees (which I discussed in an earlier post, can be very good for the trees but you don’t want to overdo it). I also applied these tree guards. There are two reasons for this. The first, is that various […]

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  4. Mulching 101 — Your Questions Answered – The Daily South | Your Hub for Southern Culture

    […] is called a “mulch volcano.” It’s bad for several reasons. Tree roots can grow into the mulch instead of the soil, making […]

    May 12, 2013 at 8:00 am
  5. Grumpy Gardener (His Benevolence)

    Sonia,
    Don’t disturb the roots that are already there. Next spring, apply a 1-2 inch layer of fresh mulch around the tree, but do not let the mulch rest against the trunk. Pine straw stays in place better than big pine bark chunks. If Bermuda spreads into the mulch, pull it by hand or spray it according to label directions with Grass-B-Gon. You can get this at home and garden centers.

    November 25, 2011 at 11:55 am
  6. Sonia

    Hello! I see all the info about the volcanoes and couldn’t agree more. We bought our house 3 years ago and had crazy amount of mulch piled around our bushes and our small Maple tree in the front of the house. I tried to dig into it and take the stuff of but the roots are already grown into it all over and I am worried that I would hurt the tree if I tried to level it down a little. This summer couple brunches died and I am worried I will loose the tree if I don’t do something. I feel like I should put another layer of mulch on it to prevent from the cold and the horrible droughts we get here in NC every summer but it just doesn’t make sense if it washes right off. We even got our “super” Bermuda grass growing in it now. Please tell me what I should do with it. It’s at least 13-15″ high. Thanks

    November 22, 2011 at 3:15 pm
  7. Grumpy Gardener (His Magnificence)

    Beth,
    Don’t try to lift it until after it’s dropped its leaves in fall. Since it was just planted this year, replanting it shouldn’t be too difficult.

    August 8, 2011 at 2:42 pm
  8. Beth@UnskinnyBoppy

    Thanks for that info, Ken. Now I just need to remember to actually DO it. 🙂

    August 7, 2011 at 2:29 pm
  9. Ken Schmidt

    Since the crape myrtle was just planted this past february, the roots have likely not grown much (“first year sleeps, second year creeps, third year leaps”). I would wait until fall dormancy and then dig it up and replant it at the correct depth. Tamp soil firmly beneath the rootball before setting. the flare of the trunk should be at finish surface grade.

    August 7, 2011 at 1:49 pm
  10. Beth@Unskinny Boppy

    I planted a crape myrtle in my front yard in February. I’m afraid I might have buried it too deep to start with and now after it’s settled it’s gotten even deeper just like you described. Is there a way to raise it up without disturbing it too much? It’s blooming right now and I hate to mess it up during it’s first blooming season.

    August 6, 2011 at 5:19 pm
  11. Grumpy Gardener (His Magnificence)

    Actually, mulching with a layer of attractive gravel (not white rock or lava rock) has some advantages over shredded hardwood mulch. Water and air penetrate more easily and roots grow down and not up into the mulch. Of course, gravel doesn’t decompose into organic matter, but you can’t have everything.

    August 5, 2011 at 1:57 pm
  12. Freda Cameron

    It took me awhile to get my husband to understand that what the “professional” landscapers were building around the trees wasn’t normal….because every yard in every high end neighborhood has volcanoes of mulch. Who started those volcanoes anyway?
    Now, he’s on to gravel (for certain plants) and that’s working better than I ever imagined (so far… got to get through winter with it).

    August 4, 2011 at 4:45 pm
  13. Grumpy Gardener (His Magnificence)

    Well, if HGTV says to use red mulch, who am I to argue? Answer: I’m the Grumpy Gardener!! That’s what I do!

    August 3, 2011 at 4:52 pm
  14. esh

    Thanks goodness someone is willing to come out against red mulch and other dyed mulches! You are my hero.

    August 2, 2011 at 9:23 pm
  15. Jeff

    Watch it – they use red dye mulch on HGTV, so it has to be the trendy thing to do.
    I think the mulch volcano must be written into Hoover’s city code or something because I see this done everywhere.

    August 1, 2011 at 10:08 pm
  16. Jean

    Another reason is you can spend a gazillion dollars on mulch every year not to mention your back at shoveling all that!

    August 1, 2011 at 9:25 am

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