Are Soaker Hoses Safe?

By Cynthia Lee Riskin

With drought predicted for the west, southwest, and south through June 2015 (National Weather Service March 2015), many conscientious vegetable gardeners will try to conserve water by using soaker-hoses, those bumpy black hoses that weep water onto the soil through tiny pores.

Brussel sprouts and red lettuce
Soaker hoses are made from fine-crumb rubber, usually recycled from vehicle tires. Research strongly establishes that tire particles leach heavy metals, carcinogens, and mutagenics, among other toxins. Yet soaker hoses have not been studied for potentially increasing the toxicity of edible plants. Are they really safe to use safe on our edible plants?

Soil in the City
Urban soils already contain high levels of heavy metals (Murray et al. 2011) from years of household runoffs—chemicals from pesticides, cars, painting, cleaning, and more. Adding soaker hoses made of crumb tires might exacerbate the problem.

Whether plants take up enough heavy metals to be toxic, however, is a complex equation, depending on a slew of interrelated factors, including:
• Soil pH (Costello 2003) and texture (Singh and Kumar 2006; Murray et al. 2011)
• Temperature (Murray et al. 2011; Lim and Walker 2009)
• The size of the rubber particles (Gaultieri et al. 2004)
• Chemical composition of irrigation water (Singh and Kumar 2006)
Furthermore, the plant species and even the cultivar can affect a plant’s uptake of zinc and other heavy metals (Murray et al. 2009 and 2011).

Growing Healthy Food
If you’re looking for the key to ensuring that your vegetable patch grows healthy food, however, I’m sorry to disappoint you. Too many factors are involved to predict the toxicity of what we grow in our gardens.

A good way to get more information is to contact your local extension agent for a list of laboratories that test soils not only for nutrient composition but for heavy metals. Although this information won’t guarantee you’ll be able to grow heavy-metal-free produce, it’s a step in the right direction while we wait for more research to be done.

Cindy Riskin is a Master of Environmental Horticulture and freelance journalist raising edible plants, an unkempt ornamental garden, and elderly mutts in Seattle, Washington.

NOTE: This article is excerpted from a longer one soon to appear in Cindy Riskin’s upcoming blog, tentatively named Muddy Fingers Northwest. Please contact Cindy Riskin at for an advance copy or the blog’s web address.

1. Costello, Laurence Raleigh. 2003. Abiotic disorders of landscape plants: A diagnostic guide. Oakland, Calif.: University of California, Agriculture and Natural Resources. P. 117.
2. Gualtieri M., M. Andrioletti, C. Vismara, M. Milani, and M. Camatini. 2005. Toxicity of tire debris leachates. Environment International 31 (5): 723–30.
3. Lim, Ly, and Randi Walker. 2009. An assessment of chemical leaching releases to air and temperature at crumb-rubber infilled synthetic turf fields. Albany, N.Y.: New York State Department of Environmental Conservation.
4. Murray, H., T.A. Pinchin, and S.M. Macfie. 2011. Compost application affects metal uptake in plants grown in urban garden soils and potential human health risk. Journal of Soils and Sediments 11 (5):815–829.
5. Murray, Hollydawn, Karen Thompson, and Sheila M. Macfie. 2009. Site- and species-specific patterns of metal bioavailability in edible plants. Botany 87:702–711.
6. National Weather Service Climate Prediction Center. March 19, 2015. U.S. Seasonal Drought Outlook. NOAA/National Weather Service National Centers for Environmental Prediction.
7. Singh, S., and M. Kumar. 2006. Heavy metal load of soil, water and vegetables in peri-urban Delhi. Environmental Monitoring and Assessment 120 (1-3):1–3.

Nature’s Poisons

Nature's Poisons
An early 17th century “plague panel” from Augsburg. Public Domain picture courtesy of WikiCommons

It’s more than a little bit intimidating to be a part of the Garden Professors team, since I have no advanced degrees, and my undergraduate degree is in Mathematics, with no formal training in Botany, Horticulture or Plant Science at all.

I am, however, an avid and active hobby gardener; I read a lot; and I have a life-long love of learning and sharing what I’ve learned with others, which led to a nine-year stint as a county Extension Educator, implementing a county wide mosquito management program for West Nile, with additional responsibilities for pesticide education and consumer horticulture.

So, what I hope to do with my space here on the GP site, is share some of the other blogs that I read on a regular basis … ones I’ve learned to trust for either the expertise, or writing style, or some additional insight into plants or gardening, or issues that arise in gardening circles.

First up this week … Natures Poisons, a blog written by Dr. Justin Brower a forensic toxicologist – that’s someone who is employed CSI-like, to investigate possible crimes related to toxicology.

His blog isn’t directly related to his profession, however … as Dr. Brower explains:

I also like plants and gardening, and seeing how there are thousands of plant based poisons, there’s no shortage of material.

Some things I will write about:

•Nature’s Poisons – all types chemical and biological
•Interesting poisonings – recent and historical
•Old uses of Nature’s Poisons

So he’s a gardener, like me, and the rest of you folks who follow the GPs.

I like the blog, not only for the wit and wisdom, but also because it puts a realistic perspective around the idea of “natural” … something which we gardeners often mistakenly equate with benign.

Plants make chemicals to protect themselves from being eaten, and the science behind that, and our use, and avoidance of them, is fascinating.

To get you started exploring the blog, here’s one of my favorite posts there discussing Horseradish, or Armoracia rusticana

Not only do you learn a lot about glucosinolates, and other chemicals in horseradish, but also a peek into the mind of a scientist.

Back inside the warm confines of the house, I cut off the tops of the horseradish roots, rinse off the dirt under water, and scrub them clean with a wash rag.

The “typical” method of preparing horseradish is to grate or grind the horseradish with an equal amount of water, wait a few minutes for the allyl isothiocyanate to build up to the desired hotness, then quench the reaction with a tablespoon or two of vinegar. Throw in a pinch of salt, and you’re done.

You’re always cautioned to do this in a well ventilated area or outdoors.

But screw that.

One, it’s cold outside, and two, and most importantly, I’m a Scientist.

If you like the blog, you’ll likely also like this book by Amy Stewart … Wicked Plants.


Organic insecticides that will get you high


Plants are crazy chemical factories, synthesizing a whole host of compounds that we use for flavoring and dye and medicine and… getting high. And why are they making all these chemicals? They’re certainly aren’t doing it for our sake… no, quite often they’re trying to kill something – usually insects — and it just so happens that sometimes our brains and bodies react differently enough that instead of killing us, they make us high. Well, and sometimes they kill us too.

Nicotine, the addictive force behind cigarettes, is a potent natural insecticide. if you’ve heard of neonicotinoids, the pesticides that some are concerned with in relation to honey bee health, they’re synthetic insectides based on the chemistry of nicotine, and like it, they effectively kill insects. No word on if anyone has tried smoking them yet.

Opium poppies are full of a thick latex loaded with chemicals like morphine and codeine, to name a few, which are obviously used as pain killers, and of course opium is taken directly or processed into more potent forms like heroin. The research on these chemicals indicates multiple possible functions, acting to prevent damage by herbivores (like insects), and possibly also acting to prevent pathogen damage and maybe even a more structural function in strengthening cell walls in response to damage  (see: I didn’t find any research looking directly at opium’s ability to kill insect pests. Probably because that type of research is usually aimed at a practical solution to pest problems, and even if heroin proves to be a potent insecticide, I doubt anyone would issue and extension bulletin recommending you use it to control your whitefly…

But that lack of practical application didn’t stop a researcher from publishing a paper titled  Cocaine as a Naturally Occurring Pesticide in which they found that cocaine was highly effective in killing tomato hornworm! Organic growers, take note! Maybe THAT’S why organic tomatoes are so expensive at the farmers market…

In any case, it is fascinating to note all the interesting, sometimes useful, often dangerous chemicals that have evolved thanks to the on-going chemical arms race between plants and the things that try to eat them. We’re the accidental beneficiaries – and sometimes victims – of that very, very old battle.

Rubbing salt into wounds

Last week I posted about some horticultural disasters I witnessed in the Czech Republic.  This week the chamber of horrors is little closer to home; virtually in my back yard to be specific.  Our property backs up to US 127, the main North-South through route in our area.  It’s a limited access highway with a posted speed of 70 mph, which means an average speed of 82.7 mph.  It also means the road is regularly salted whenever it snows during the winter.  As a result, some plants along the highway really take a beating, sometimes with some interesting results.

On Friday I received an email from Susan Gruber, our Undergraduate Advisor, who also commutes on US 127.  “Hey Bert, Have you seen the pear trees on the east side of NB 127 just south of the Round Lake Road (and Price Rd) exits?  Street side fried, shows up great with flowers on the other side. Also same trees planted at the same time doing great by the ramps, farther from the road, slower traffic, some up on the berms etc. Make great GP fodder, but I didn’t have a decent camera or the guts to pull over and do phone photos in rush hour.”

Unaffected pears upslope and away from salt exposure

Indeed I had seen the trees.  As Susan noted, the sides of the trees facing the highway were fried, the opposite sides were in full bloom.  I got a few photos over the weekend but the effect was a little less striking than earlier in the week when the trees had blooms but hadn’t begun the leaf out.

Pear trees in the line of fire

The planting illustrates a classic example of wrong tree-wrong place.  Interestingly there are several crabapples that were installed as part of the same planting project that seem to be doing well.  Selecting trees for exposure to deicing salt is a dicey proposition since, like this example, most of our information is anecdotal.  Where the effects of deicing salt on plants have been systematically examined, the studies may focus on only soil exposure or only aerial deposition; whereas trees in the real world get it with both barrels.

Eastern white pine after one winter at a rest area along I-96 east of Lansing. An ideal proving ground for salt tolerant plants.

Ironically a colleague of mine in our department and I put together a proposal several years ago for our state Department of Transportation (MDOT) to identify salt tolerant plants for roadside plantings.   Our plan was to install a series of replicated plantings of perennials (trees, shrubs, herbaceous perennials) at highway rest areas throughout the state.  We would then correlate plant performance with degree salt exposure and identify plants that could survive, grow and maintain their aesthetic value under the highest salt loads.  Initial discussions were positive until the proposal worked its way up the chain of command.  Finally it was determined – I am not making this up – that MDOT could not participate in a project on indentifying plants that were tolerant of deicing salts because that means they would have to admit that salt was causing a problem.  OK; just don’t tell the trees on US 127…

In our studies we rate plants on a scale of 1 (alive) to 5 (dead).  These are class 4 (wish they were dead…)

The invisible, insidious presence of heavy metals

I spent the last two weeks in Spain, combining business with pleasure.  It’s interesting when something that starts out as part of the pleasure ends up being business instead.

Charlotte translated this sign for me – it’s historical information. Note the brightly colored mine tailings in the background.

My daughter is teaching English in Mazarrón, a small town in the province of Murcia. The climate there is very similar to southern California, though drier and not as warm: it’s pretty much a scrubland ecosystem. Since we both enjoy hiking, we decided to take advantage of exploring the abandoned mine sites.  Unlike such sites in the United States, there are no restrictions to hikers and in fact there’s signage explaining the history of the mines. This is a popular hike after a rainstorm because of the unnaturally red pools that form in the landscape.

The abandoned mine works; these buildings are over 100 years old, though this area was mined since Roman times.

It took some Internet research to find out that lead, silver and zinc were the minerals of interest extracted from these mines.  For those of you who aren’t aware of how ore processing works, it includes adding various chemicals to crushed rock to solubilize and isolate the desired minerals. The leftover tailings are nearly always highly acidic and full of environmentally available heavy metals.  The various metal oxides and sulfides that formed at Mazarrón are vividly red, orange, and yellow, and there is a pervasive sulfur smell throughout the site. If this isn’t hell on earth, I don’t know what is.

Mountains of mine tailings

So it was really quite a shock to both of us that not only could we walk into this mine site, but that there were no warnings regarding exposure to whatever toxic chemicals might be in the soil and water.  We took pains not to touch anything – but others were not so cautious. Some hikers ahead of us watched their dog cavort through the largest of the pools, and later took photos of each other on the mine tailing spoils.

Visitors and dog and red pool of ????

Yes, the dog went in the water

And then a photo op on the side of Spoils Summit

This hideously beautiful landscape was unearthly, primarily because there was absolutely nothing alive in it.  No plants, no insects, no birds.  Along the edges of the mine tailings there were spring flowering shrubs, bees, and birds, just as one would find elsewhere in the region. (But not in the spoils.  What an apt name…)

A blood-red seep into the pond

Crystals forming as water dries in the pools

Just off the side of the tailings, life continues

How do the mines of Mazarrón fit into gardening?  Unlike this mine site, where the evidence of heavy metal contamination was clearly visible, it’s not so obvious in our garden soils. The residues of arsenic-containing pesticides, leaded gas, zinc from car tire wear, and other possible contaminants are unseen and unknown unless we have soil tests done to confirm their presence or absence.  Yes, it can be expensive to have these tests done, but if we are handling our soils, breathing the dust, and eating the plants that grow there, wouldn’t it be smart to find out what’s there first?

A Note To Horse Owners

Every once in awhile I get to work with really, really cool people who do really, really cool work.  This is one of those times.  About a year ago I received a message from Dr. Stephanie Valberg, a Professor over at the University of Minnesota’s Equine Center.  It seems that she was interested in looking at a deadly disease called Seasonal Pasture Myopathy which she thought might have something to do with horses ingesting maple leaves.  Specifically, at the time she contacted me, she thought that this disease might be associated with horses ingesting tar spot, a common disease that maples get. Seasonal Pasture Myopathy is a particularly nasty disease because it is fatal in over 90% of cases, and the death is far from painless.

After doing site visits to many farms where this disease was found, she discovered something very important: Every farm had box elders in a location where horses could feed on the seed when they got hungry.  And for most of the farms, horses were also dealing with scant pickings in terms of food.  They usually had sparse pastures and not much supplemental hay.  So, in these conditions, the horses might find box elder seed attractive, or at least palatable.

After a literature search, Dr. Valberg discovered an old article showing that box elder seeds could very well contain a toxin, hypoglycin A, which might cause this disease if they were eaten.  After testing the seeds for the presence of this toxin (Done by a friend of mine, Adrian Hegeman, located here in the University of Minnesota’s Department of Horticultural Science) it was established that, Yep, box elder seeds have this toxin, and if your horse eats them, it might be in trouble.  You can find out more here.

Right now more work is going on to see if this toxin is more or less present in box elder trees that are under stress, if it is present in other parts of the tree besides the seeds, and at what time of year the toxin might be most present in the seeds.  It also looks as though some other maples may have this toxin in their seeds, most notably sycamore maple.

All in all, having the opportunity to watch this work unfold has been one of the highlights of my career.  It was like watching an episode of House unfold in real life.  And the great part is that this work has the potential to save the lives of dozens, if not hundreds or thousands, of animals.  So if you have horses, and box elder or sycamore maples in your pasture, be careful!

Toxic mulch: When shredded bark goes bad

We typically think of mulching landscape beds as a good thing.  And it usually is; helping to conserve soil moisture, reducing soil temperatures and contributing to soil organic matter.  Recently, however, I received an e-mail from a local landscaper that reported severe damage to annuals and perennials in a landscape bed immediately after applying hardwood mulch.  The problem, sometimes referred to as ‘sour mulch’ or ‘toxic mulch’, occurs when mulch is left is large piles and undergoes anaerobic conditions.  This results in the production of acids and other compounds that can volatilize when the mulch is placed in beds, especially during hot weather.  These vapors can quickly damage annuals and other sensitive plants.  Mulch in this condition is often characterized by a ‘sour’ smell.  If you suspect your mulch has gone sour, spread it out before use to allow toxins to dissipate and water thoroughly either before or immediately after application.  The University of Arkansas Extension has a nice fact sheet in the subject “Plant injury from ‘sour’ wood mulch.

Fried Gerber daisy

Sedums are usually pretty tough…

And, yes, I did steal the title of this post from one of my all-time favorite ‘Far Sides’…