Mulch: More than Just a Pretty Face

By: Alison O'Connor, Horticulture agent, Larimer County Extension

We horties gossip as much as any other office clique...generally about bad gardening advice.  Usually I just roll my eyes at the stuff (something I perfected as a teenager), but this time…it struck a nerve.  Maybe it’s because I’m a huge advocate of that shredded wood we call "mulch", but I felt the need to blog about it.  Whether you agree with me or not…

Fellow blogger, Tony Koski, emailed this link to me and a few colleagues last week, from a blog, called “Grounded Design”.  The author, Thomas Rainer, does have some valid points.  But I just can’t get on board with his philosophy about hating tree mulch rings?  If you choose not to read the article, Mr. Rainer suggests the following about mulch rings at the base of trees:

--They are “ugly” and “have got to go” and “make Swiss cheese out of a continuous lawn”

--They don’t make mowing easier; he states that it’s not difficult to mow around trees, and mulch rings actually require more maintenance [compared to turf]

--Rather than mulching, he suggests planting continuous vegetation to the base of the tree

I do agree with Mr. Rainer on a couple counts.  First, improper mulching is very bad for the tree.  Volcano mulching and covering the flare does lead to stem girdling roots, creates a textural interface that can reduce oxygen availability to the tree’s roots and disrupt water movement to the root ball.  Second, he admits that it does keep mowing equipment and string trimmers away from the base of the tree—one of the main reasons I advocate for mulch.  How many of you have seen trees nicked or wounded from equipment?  It’s tough on the tree (and often leads to decline or death), and it looks horrible.  I’d gladly pick the “Swiss cheese” look over gaping trunk wounds any day. 

If that doesn't make you wince! Ouch.



Clearly the tree "guard" failed.  Mulch may have prevented this from happening.

While his expertise in landscape architecture is admirable…I wonder how he’s never run into the difficulties of growing turf (or other vegetation) under shade trees?  This is a very common question I get each year—“Why can’t I grow [insert plant here] under my mature tree?”  More than likely, it’s because it’s just too darn shady.  Turf needs a minimum of 4-6 hours of sun to grow (more like limp along).  Plus, the tree is sharing water with the lawn—and neither are likely getting enough.  So why would you want to increase the irrigation, and risk killing the tree from overwatering it, in order to grow some grass?  Instead, use mulch and focus your watering efforts on just the tree!  While you can plant shade tolerant perennials or groundcover under trees, I don’t think they are easier to maintain than mulch.  (I just spent the weekend cleaning up my yard—let me tell you—those perennials can be cantankerous.  The scratches on my arms prove it.)

My mother-in-law says it best: mulch is like make-up for the landscape—it looks good and has many benefits…if applied correctly.  In most of our urban areas, water restrictions begin today.  It’s been proven than mulch can reduce water evaporation from the soil surface by up to 70%.  That’s significant.  In addition, a study conducted at the College of DuPage in Illinois by Morton Arboretum staff found that trees that were mulched had significantly greater caliper, crown and root development compared to those with turf growing up to their base (Green and Watson, 1989).  Another study found that mulch modified the soil environment, increased root and shoot growth and aided in plant establishment of desert willow, while turf impaired its establishment (Kraus, 1998).

Trees with mulch rings...does it really look that bad? Is it better to sacrifice tree health at the expense of design?  Trees struggle enough in our tough Colorado climate.

My advice: be sure to mulch, but do it correctly.  Don’t volcano mulch.  Don’t mulch to the trunk (keep it a few inches away).  Don’t have too thick of a layer—2-4” is perfect. Don’t overwater areas that are mulched, since it does hold soil moisture better than unmulched areas.  Keep your rings a diameter of 2-3’ wide (but the wider, the better).  And find a mulch that works for your location and your plants.  So here’s to helping trees with…trees….just little chipped bits of them.