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.)

Whoo hoo!

I promise I’ll post something more substantial today…but I had to pass this email message along that I received this morning.  Way to go colleagues and commenters!

Hi Linda,

Your new weblog, the Garden Professors, is an impressive piece of work! I plugged it today in the consumer horticulture CoP blog [http://www.consumerhortcop.wordpress.com].

Regards,

Bill Hoffman
National Program Leader (Ag Homeland Security)
CSREES/USDA

More Good Stuff from the Garden Writer’s Conference in Raleigh

I should add “in absentia”… Played hooky from the convention center Thursday afternoon for a trip out to Plant Delights Nursery, Inc. with my former grad student and plant geek extraordinaire, Paul Westervelt. We followed proper Plant Delights etiquette: you make an appointment to visit at a time other than open house or tour. I teach herbaceous landscape plant i.d. as well as ornamental plant production courses, and take every opportunity to bring back images of new technology, growing systems, and great plants to my students.  Since Paul is a now a grower for a large nursery, he’s also keen to learn anything he can.

We certainly didn’t go to shop [“She lies!”].


Tony amongst the yucca pups.

Even though we arrived a good hour before our appointed time (we were…excited), and even though a throng of 500+ salivating conference attendees were to besiege him and his staff the next day, owner Tony Avent very kindly made time to give Paul and me a personal tour of the back 40: where the real action is. Tony patiently answered our gazillion questions and filled our pockets with seeds. The propagation houses and trial areas have more amazing plants than you can shake a stick at. Many are one-of-kind hybrids or species. The vast Colocasia trials actually gave me goose bumps – alas, no photos were allowed. A walk through the display and trial gardens (Juniper Level Botanic Garden), resulted in several trips back through the retail houses to find that OMG! plant we just saw. We topped our visit off with the purchase of way too many yummy plants. Delightful, indeed!


The trial and breeding collection of Epimedium species and hybrids. Who knew there were that many???


North Carolina or Hawaii?? That’s  Colocasia ‘Diamond Head’.


I’m in an Agave/Yucca phase and this isn’t helping a bit.


Paul demonstrates “The Joy of Plant Shopping”.

Baring it all, again.

Earlier in this blog we had a rather robust discussion about the merits of transplanting trees bare-root.  Bare-root transplanting has had a renaissance in arboricultural circles, based in large part on the work of Dr. Nina Bassuk and her colleagues at the Urban Horticulture Institute at Cornell.

As our bloggers noted, transplanting trees bare-root has advantages over balled and burlap trees (larger portion of the root system stays with the tree) and over container-grown trees (more natural root system development).   One disadvantage of bare-root trees is the need to protect roots from desiccation during storage and handling.  Also, some trees respond better to bare-root treatment than others.  Nevertheless, I think we will continue to see increased interest in bare-root planting.  One notable trend is planting relatively large-caliper (4” and larger) trees bare-root.  This phenomenon has coincided with the development of the air spade, a tool which produces powerful a jet of air that allows arborists or nursery workers to carefully excavate an entire root system with minimal disturbance.  Unlike digging a tree with a traditional tree spade, the air spade allows nursery workers to maintain virtually the entire root system when lifting a tree.  Last week,  my esteemed colleague, Dr. Tom Fernandez, and his Nursery Management class at MSU worked with Paul Swartz, MSU campus arborist, to lift a 10” caliper weeping white pine from our campus nursery.  Members of the class took turns using the air spade to excavate the entire root system of the pine.  Since the class is divided into lab sections that meet throughout the week the process was spread over several days.  After each lab period exposed roots were covered with wet burlap to prevent drying.  By the end of the week the tree was ready for lifting and was transported via flatbed truck to its new home at the front entrance to the MSU Horticulture Teaching and Research Center.   Paul Swartz reports that he has successfully used the air spade to move several large specimens on campus and the technique is especially useful for moving trees from tight spots that can’t be reached with a mechanical spade.  As more and more arborists acquire air spades look for this technique to become more common.

NOTE: Photos courtesey of Dr. Tom Fernandez.


The air spade uses a stream of compressed air to excavate roots.


Note the extent of the root system.  A 90″ mechanical spade would have missed at least half the roots of the tree.

Once the roots are excavated the tree is ready for lifting.


The pine resting comfortably at its new home.

My Favorite Class Project

Every year  I teach a class called nursery management.  In this class students have the opportunity to try all kinds of different growing techniques out in the nursery.  They get to use a tree spade and prune and all kinds of other stuff.  But something else that I have the students do is to make hydroponic systems for growing plants.  No, hydroponics is not a common technique for growing plants in a nursery, but to grow plants hydroponically you need to know what you’re doing, and so this is a convenient way to make the students think about the plants they grow and what these plants need to prosper.

To start this project I give the students a water pump and an air pump (courtesy of our friendly neighborhood drug dealers — no, seriously — when the cops bust pot growing operations they give us the equipment that they’ve confiscated after they’re done using it as evidence.  Much of the equipments is new, some is very high end.)  Then I divide the students into a few groups, tell them what they’re growing, and give them two weeks to come up with a growing system and a nutrient solution to grow their crop (I do allow them to use our stock hydroponic solution, which will grow the plants, but won’t win anyone any prizes — most groups choose to use this as a base solution and then add to it.).  The group whose plants grow the largest after twelve weeks wins a modest bonus to their grade.

So, what do we have for set-ups this year?  Some very, very cool ones!  First, we have a number of groups who went with a simple, non-circulating system, as seen below.  Basically just an air-hose and a container filled with nutrient solution.

Another group decided to use a flood and drain system.  They use a timer to trigger the water pump to fill a tray with nutrient solution for five minutes every few hours.  This hydrates the containers which hold the extremely well drained ceramic beads in which the plants are held.

And finally, one group decided to use a capillary action system where the base of the container is filled with nutrient solution which is wicked up into a well drained media (a combination of rockwool, vermiculite, and perlite) into which the plants are placed.  This group decided to lay their plants on their sides to encourage extra root growth.

I’ll let you know in about 12 weeks which group wins!

Eat your veggies! (But not the arsenic, or the chromium, or the lead…)

vegetables_jpg.jpgThe last few years have been a perfect storm for the resurgence of home vegetable (and fruit) gardens.  Grapevines are trellised along sidewalks, herbs replace the grass in parking strips, and tiny gardens of carrots and lettuce are shoehorned into any available spot.  It’s all good  – but we need to be particularly careful about what those plant roots might be taking up along with nutrients and water.

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1)  Contaminated soil.  Many urban (and suburban, and even rural) soils are contaminated with heavy metals, pesticides, and/or industrial wastes.  Lead is commonly found in soils near roads (from the old leaded gasoline we used to use) or from old lead-based paint chipping away from houses.   Arsenic is a very real problem in North Tacoma soils, for instance, thanks to the smelter that operated there for decades.   Overuse and incorrect use of home pesticides will leave residues in the soil for years.

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2)  Contaminated compost and soil mixes.  Many of the same contaminants mentioned above can be found in unregulated composts and soil mixes.  (More on this topic here.)

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3)  Treated lumber.  The old treated lumber (CCA = copper, chromium and arsenic) is no longer being sold, but it’s out there.  These timbers should not be used around vegetable gardens, as they will leach their heavy metals into the soil.  Vegetables vary in their ability to take up and store these metals.  (More on this topic here.)  Likewise, rubber mulches may leach unwanted chemicals into the soil and should not be used around food plants.  (More on this topic here.)

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What can you do to avoid these problems?  A few things are quick, easy and cheap:

1)  Have your soils tested.  I’ve mentioned this in an earlier blog on urban soils.  It’s the best way to find out exactly what you have in your gardens – the good and the bad.

2)  Use only certified composts and soil mixes.

3)  Plant in containers if your soils aren’t safe for food.  This is especially easy to do with perennial herbs, which can be kept like any other container plant on your deck or porch for years.

4)  You can also replace the soil in your vegetable garden.  This isn’t quick, easy, or cheap, but is a solution for some people.