Rubber mulch rubs me the wrong way

I’ve been receiving a lot of questions about rubber mulch lately.  For those of you not familiar with the product, it consists of shredded tires that can be dyed and used on ornamental landscapes or under playground equipment.  In fact, the Obamas had this material installed underneath their children’s play structure at the White House.  It seems an ideal way to recycle the 290 million scrap tires we generate annually.

  

But is it?

It’s not effective:  One of the main reasons we use mulch is to suppress weeds.  Research has demonstrated that organic mulches such as wood chips, straw, and fiber mats control weeds better than rubber mulch.

It burns:  You’ve heard stories about piles of scrap tires catching fire and burning for weeks.  Well, those same flammable compounds are in rubber mulch, too.  When compared to other mulch types, rubber mulch is the most difficult to extinguish once ignited.  In fact, some parks and playgrounds no longer use rubber mulch or rubberized surfaces because vandals have figured out that rubber fires cause a LOT of damage.


It breaks down:  Although sales literature would have you believe otherwise, rubber is broken down by microbes like any other organic product.  Specialized bacterial and fungal species can use rubber as their sole food source.  In the degradation process, chemicals in the tires can leach into the surrounding soil or water.

It’s toxic:  Research has shown that rubber leachate from car tires can kill entire aquatic communities of algae, zooplankton, snails, and fish.  While part of this toxicity may be from the heavy metals (like chromium and zinc) found in tires, it’s also from the chemicals used in making tires.  These include 2-mercaptobenzothiazole and polyaromatic hydrocarbons, both known to be hazardous to human and environmental health. 

It’s not fun to be around:  When rubber mulch gets hot, it stinks.  And it can burn your feet.  Yuck.

The EPA’s website says this about scrap tires:  “Illegal tire dumping pollutes ravines, woods, deserts, and empty lots.  For these reasons, most states have passed scrap tire regulations requiring proper management.”   So if we have legal tire dumping (in the form of rubber mulch), does that mean it doesn’t pollute anymore?

(You can read a longer discussion on rubber mulches here.)

Buddleia or Buddleja?

I recently heard that Mike Dirr has come out with the next edition of his book on woody landscape plants. Dr. Dirr (I can’t seem to bring myself to call him Mike, even after all
these years) was my major advisor in graduate school, so I’m really looking forward to getting it.  In the meantime I heard that he included a section on my thoughts about how to spell the scientific name of the butterflybush, a plant that I worked on to get my Ph.D..  Some people spell it Buddleia, but most go with the Buddleja spelling  — but it looks really silly.  So, while I’m not sure exactly what Dr. Dirr wrote, I thought I’d give you my two cents worth.

By the way, any of you out there yelling and screaming that I shouldn’t be promoting an invasive weed should be ashamed of yourselves.  I spent years working on this plant and I
refuse to believe that all of my work was for naught!

But back to the name. First of all you need to understand that the Butterflybush was originally named for a botanist named Adam Buddle.  Buddle didn’t discover this plant.  Nor was he directly involved with its naming, being an expert on mosses.  Besides, he wasn’t even around when Butterflybushes were discovered by the western world around 1730 (Buddle died in 1715).

Buddleja was first mentioned in Species Plantarum, a book by Linnaeus.  And, when it was listed there, it did have that j in it.  OK, so far it makes sense to spell the name Buddleja.
BUT, in his later works, though this plant was spelled Buddleja in the text of the book (at that time stylized print settings meant that i’s were printed as j’s u’s as v’s as s’s as f’s), in the index – where the stylized text wasn’t used – Buddleia was spelled with an i.  Hence I submit to you that Buddleia should be spelled with an i – though I’m not nearly as fanatical about it as I once was.

A Brief Discussion on the Wisdom of Barberry as Median Plant

We never know who to blame (or, rarely, thank) for roadside or median plantings. State D.O.T.? Local municipality? Subcontractor to either of the previous?

A few years ago, this appeared in the median of the Highway 460 bypass – the main road leading to Virginia Tech:

I am somehow reminded of Sideshow Bob from The Simpsons…

Two hedge rows. One of  green Japanese barberry (Berberis thunbergii, cultivar unknown); the other of the purple form (Berberis thunbergii var. atropurpurea) Side by side, they make their way up the median, alternating from the right-hand side of the culvert to the left, like two caterpillars in love.  Ooooh, lovely! Or at least SOMEBODY thought so.

Issues: 1) Barberry is a prolific fruit-setter and has made several state’s “Invasives” list.  It’s outright prohibited in Massachussettes (can’t buy, sell, or import it).  In our Blue Ridge Mountains of southwestern Virginia, it is popping up with startling regularity in state forests, road sides, open fields, etc. Interestingly, most of what I’ve seen is the purple form.  2) It’s very thorny. Which means most of the time it is adorned with plastic bags and other perforatable garbage.  3) They are actually mulching, pruning, and weeding this mess, which stretches for at least 2 miles. Best use of state budget/manpower??

I realize purple Japanese barberry is one of the bread-and-butter staples of many nurseries and garden designers. Folks just love the deep reddish-purple foliage.   Virginia Tech’s school colors are maroon and orange, so this is the go-to shrub for campus landscapers and ardent alumni desiring that particular color scheme (see below for our “living VT”). Very fun!  Growing next to a trillium on our section of the Appalachian Trail? Not so much.


Approximately one gazillion people get their photo made next to the VT logo each year – pretty good public relations for a noxious weed.

Modern day torture stakes

Torture stakes were used centuries ago as a slow means of executing prisoners.  Unfortunately, the practice lives on every time someone incorrectly stakes a newly planted tree.  Though I’ve written about tree staking before (click here to read more), I’ll use today’s blog to demonstrate another unintended result of improper staking – decapitation. A normal tree develops taper as it grows.   At eye level, a tree trunk is narrower than it is at ground level:  that’s taper.  As the trunk flares out and morphs into roots (Figure 1), a buttressing structure is created that allows trees to remain upright, even under windy conditions.

Root%20flare.jpgFigure 1.  Trunk flares as it meets soil and roots begin.

A tree that’s been staked too high, too tightly, and/or for too long does not have this structural protection.  Instead, the staking material creates an unnatural pivot point, which is not structurally capable of withstanding wind.   When the inevitable windy day comes along, the trunk snaps at this point (Figures 2-3):

Decapitation.jpg     Decapitation%20close.jpg
Figures 2 and 3.  Tree decapitation, up close and personal.

Unlike the victims of the original torture stakes, trees don’t necessarily die after breakage.  They are, however, permanently deformed and have little aesthetic value.  If trees need to be staked at planting (and many times they do not), staking needs to be low and loose to allow taper to develop normally.  (More information on proper tree planting can be found by clicking here.)

The Pile Of Ash On My Floor

Part of the problem with being a professor is that companies assume that I have a bottomless supply of funds to test their products and that it is, in fact, my duty to do so.  And of course they assume that this testing will ultimately find their product useful.

The truth is that I do love to test things, but I don’t have the funds to do the comprehensive tests that these companies usually want, at least not without them helping out at least a little – and most of them don’t want to spend money on tests!  But many times, even if I tell them on the phone that I’m not likely to test what they’re selling they’ll send along a sample anyway, hoping that I’ll be curious enough to give the stuff a shot.  And I usually let them because, well, why not?

Anyway, that brings me to this pile of ash that is currently sitting on my floor.  A guy from a company (which I will decline to name) called me on the phone and convinced me to accept about 25 pounds of rice hulls that had been burned to ash while being used to fuel something or another (I can’t remember what and there was no note in the box).  This ash is supposedly the cat’s meow for helping the media in containers to retain water and this guy wants me to test it.  I told this guy that I was unlikely to have time for it, but he was insistent.  I guess he thought that if the stuff sat on my floor long enough eventually I’d get curious, open the box, and try it out.

Turns out he was right.

So I get this box full of ash, open it up and am immediately hit in the face with black dust which I wisely (and accidentally) inhale.  Lovely. Then I take out the MSDS sheet (Material Safety Data Sheet – required for most chemicals) and read about the problems with this product.  It turns out this stuff contains crystalline silica (no surprise there, rice hulls are full on silicon), which can cause a rapid onset of silicoses as well as being a cancer hazard (crystalline silica is a known carcinogen if it’s inhaled).

Now I don’t want to blow the danger of this stuff out of proportion.  I have little doubt that my exposure to it wasn’t enough to do anything terrible to me (just as I’m pretty sure that the two packs of cigarettes or so that I smoked during college aren’t going to eventually lead to lung cancer).  And I’m all in favor of using industrial byproducts for other purposes whenever possible.  But my goodness, this stuff is ash!  It just flies into the air!  I just can’t see how, even with the recommended protection, nursery workers could avoid inhaling this stuff on a daily basis if they were using it to pot up plants (perlite is pretty bad – but this stuff is worse) — which just seems like a heck of a bad idea.  In terms of the ability of this stuff to hold water….well, I put some into a plastic container with some water which the ash absorbed none of.  All that said, it might be possible that this stuff helps container media to hold more water, but for an unintended reason.  This ash is extremely fine.  When we mixed it with container media it quickly found its way into all of the pore spaces between the media particles making the media more like clay than media. This did potentially increase the media’s ability to retain water, but decreased its ability to hold air – which is not a good thing for young roots.  So the quick and easy summary is that rice hull ash is not the best idea for containers.

Bad roots and deceptive marketing

I guess today’s blog should be entitled “The Cranky Garden Professor.”   Really, I’m not always cranky, and when I am I go outside to do something constructive in my garden.  Last weekend I finally tackled a 5-gallon container of lavender that I’d bought several weeks ago.  I had intended to wait until fall to transplant it, but I was watering it every day to keep it from wilting.  I figured I might have better luck getting it into the soil where a good mulching would help keep the soil moist without daily watering.

So I carefully slid the lavender out of its pot and into my root-washing tub (Figure 1).  (If you’re not familiar with root washing trees and shrubs, be sure to check out my web page.  I’ve got a fact sheet and some myth columns on why it’s important to bare-root containerized and B&B woody plants before installing them in the landscape.  Please visit www.theinformedgardener.com to access the entire site, or this link for the fact sheet:http://www.puyallup.wsu.edu/~Linda%20Chalker-Scott/FactSheets/Planting%20fact%20sheet.pdf)


Figure 1.  Five little lavenders.

As I worked the potting media out of the root mass, I suddenly discovered why I was using so much water to keep the lavender happy.  It wasn’t one plant.  It was 5 separate lavender plants all placed in the container to LOOK like one large plant.  Worse, all 5 plants had some of the crummiest root systems I’ve ever seen (Figures 2-6).  They were poked into the pot like little carrots.  Most of the pot was filled with untouched potting media.

    
Figures 2-6.  The beehive is back!

What you see in these figures are root systems that look like upside down beehives.  They were obviously left in their original small pots too long and developed circling root systems.  So rather than growing outwards into the soil, they stayed in these little spirals and eventually would fuse into woody knots.   They don’t miraculously straighten out when they’re put into larger containers (or the garden).  If they did, they would have rapidly spread throughout the big container to soak up all that water I was pouring on daily.

Sigh.  Now I was cranky again.  These lavender roots were just like those I’d seen on hundreds of landscape plant failures over the last 10 years.  Since these roots were so tightly woven together there was little hope of untangling them.  So I made one vertical cut through each of the root masses (Figure 7), spread them out horizontally (Figure 8), and planted them (Figure 9).

    
Figure 7.  The cut.           Figure 8.  The spread.   Figure 9.  In the ground.

This is the worst possible time of year to transplant trees and shrubs (it’s August, after all) and I most definitely put a world of hurt on these roots.   But I will say that since I moved them I have been able to reduce irrigation, since the soil holds moisture better than the potting media.  I’ll keep track of their progress through the next 12 months.  I’m hoping they make it through this summer – if so, they stand an excellent chance of growing a decent root system over the fall and winter.

Back to the cranky part.  I really resent nurseries that deliberately bunch small shrubs together in one pot to make them look like one big plant.  It certainly cost more to buy this one pot than to buy five smaller pots.  If this isn’t deceptive marketing I don’t know what is.