The Garden Professors™

A Brief Announcement

Sometimes it’s fun to experience life unfolding around you. This past week I started my new position as the Director of the UNC Charlotte Botanical Gardens and am very excited to be working with my old friend (she’s not old – I’ve just known her a long time) Paula Gross, Assistant Director of the garden, a fantastic horticulturist, and one of the best people you could ever hope to meet. Together with our highly skilled staff we’re going to be working to bring the world of plants to people. It’s an exciting time in my life, and hopefully an exciting time for the gardens too.

That said, I’m sorry to be leaving Central Piedmont Community College. I have never seen instructors so devoted to their students as at this community college. So often at large universities professors teach because they have to, not because they want to. At community colleges, and particularly at CPCC, the opposite is true. These highly skilled instructors really care. If you are looking for a degree in horticulture I strongly recommend considering a two year school because of the cost, the attention to students, and the hands on education that most four year schools can’t compete with (I know that sounds silly, but speaking as someone who spent fifteen years working as a horticulture professor in a large university I can tell you that it’s simply the truth).

Here’s the official announcement. The only thing I’d like to add here is that we’d love to have you stop by! We are a wonderful little garden in the North of Charlotte with a lot of fascinating carnivorous plants, orchids, a great landscape collection, and a titan arum that just bloomed and which now appears to be setting seed. We hope to see you soon!

Jeff Gillman

The cardboard controversy

I’m not a fan of using corrugated cardboard as a mulch, which like other sheet mulches creates problems for the underlying soil. Long-time readers of this blog may remember several previous posts (1, 2, 3 and 4) on this topic and I won’t belabor the points made in those posts. Instead, today I’m doing to focus on cardboard itself.

First, cardboard is a generic term that can refer to many types of manufactured paper. The box you see delivered to your front door is more properly called corrugated board or containerboard. It consists of two layers of linerboard sandwiching a layer of accordion-like fluting material. The linerboard is made from sheets of pulp that may be coated to improve smoothness (more about this later). The finished linerboard is laminated using adhesives to both sides of the fluting material.

Corrugated boxes are built to be tough. — Corrugated boxes are built tough

These boxes are made to withstand rough handling and to protect the contents from the external environment. It’s tough stuff: while you might be able to bend a piece of corrugated board fairly easily, it’s more difficult to tear it in half. The more heavy duty the box, the more difficult it is to bend or tear its walls.

So let’s now consider using this tough material in your garden as a mulch. It may be coated as mentioned earlier to improve smoothness. That’s going to prevent it from absorbing moisture. The coating also reduces the ability for gases to move between the soil and the atmosphere. In fact, smoothness is measured using an air leak method – the smoothest materials have the least air leakage.

Photo credit vizpix at Flickr — Photo credit: vizpix at Flickr

A garden or landscape mulched with cardboard (or heaven forbid several layers of cardboard as part of the science-free lasagna mulch method) is now covered with a tough, relatively gas- and water-impermeable material that will take some time to break down. It’s hardly a mulch that’s going to nurture soil life.

But cardboard mulch fans swear that they find more earthworms under cardboard than anywhere else in their garden. This is almost always the first response I get from gardeners who don’t believe that cardboard causes problems. And this is where it’s important to consider earthworm behavior.

Photo credit: Kurt B. on Flicker — Photo credit: Kurt B. on Flickr

We’ve all observed that earthworms crawl to the soil surface during heavy rains; this is due in part to water filling their burrows and reducing oxygen availability (Chuang and Chen demonstrated this nicely in 2008). Likewise, the reduction in oxygen movement from the atmosphere into cardboard-covered soil would cause worms to crawl upwards in an effort to find oxygen at the soil surface.

So don’t assume your lasagna mulching draws earthworms to your garden. It’s more likely that you’re smothering their habitat.

***An update on cardboard gas permeability. We’ve just published an article comparing diffusion rates of different mulches. You can find the article here but it is behind a paywall. Here is a graphic comparing diffusion rates of various mulches. This is a logarithmic scale.
Now, until cardboard proponents publish evidence to the contrary, it’s pretty obvious that cardboard mulch interferes with gas diffusion.

***And another update on how our blog works. This post, by far, is the most popular. It generates a lot of comments. All comments must be approved before they’re posted, and I don’t approve comments that are derogatory or promote a belief in the absense of supporting science. If you want your comment to be published, be polite and provide evidence to support your statements. Otherwise, you are wasting your time.

***Another update on cardboard in your garden: A recent paper reports on PFAs (aka “forever chemicals”) in various products used for poultry bedding (among other things). Cardboard was one of the worst. The article is behind a paywall but I have access to it and was able to find the table shown here. So if you need yet another argument to NOT use cardboard as a mulch (like in “lasagna gardening), maybe “keep forever chemicals out of your garden” will do it.

**Look at the top line for shredded cardboard and then the last column which has the PFAs data. Not to mention all the other contaminants listed.**

FrankenFoodFacts

Sunset papaya cultivar — Public Domain Photo of GMO Papaya via Wikimedia Commons

The subject of Genetically Modified Organisms, or GMOs, first came to my attention sometime in the fall of 2009, not long after I started following the Garden Professors Blog.

I stumbled across a site called Biofortified, run (at the time) by a couple of grad students in the field, who were trying to accomplish the same thing that the GPs were, combatting myths and misconceptions about a subject, with research based information.

I spent about 2 years lurking there, because much of the information at the time was over my head, and seemed to be targeted to fellow scientists to help with getting the information out.

So I’m incredibly pleased to introduce you to the blog of Dr. Layla Katiraee, a scientist in a related field, but with little to no experience at all with the topic of GMOs, so spent time learning about it and sharing what she learned with the public.

She is now also a contributor to Biofortified.

One of the best things I like about the blog, is her continual checking with “the spouse” to see how her posts might be viewed from someone outside the field.

Here’s a great example:

So, the spouse has often complained that I don’t have a post with an overview of what transgenesis means and the transgenic (GMO) crops themselves. They’re scattered throughout the history of this blog, but not in a single place.

…

What does this mean? To explain, I have to go to the beginning: the working units within any cell are proteins. Proteins are made up by linking together amino acids in a given sequence. The exact amino acid sequence is defined in the cell’s DNA; the DNA blueprint for a specific protein is known as a gene for that protein. In general, one gene encodes for one protein (of course, there are exceptions). Since there are thousands of proteins, there are thousands of genes. We’re still figuring out what different genes/proteins accomplish.

Another great post on how the science of safety testing works …

The first thing to keep in mind is that there are many aspects to safety. In our example, we have to select an aspect of water safety that we want to examine: health impact, water transportation, water treatment, proper water storage, etc. For our example, we’re going to select “health impact”.

Then, we have to come up with a null hypothesis. Spouse, I know that it’s counter-intuitive and the double negatives in these statements suck, but unfortunately, it’s a key aspect of this whole article. The baseline for much of research is that there’s no impact or no difference. It’s the researcher’s responsibility to disprove that hypothesis, ie. to show that there is a difference or that there is an impact. So for our exercise, our hypothesis will be “Drinking water does not cause cancer”.

So follow her blog, FrankenFoodFacts, or follow her articles elsewhere on Biofortified, or her Twitter feed, and gain some better understanding about the science behind GMOs.

Why doesn’t my plant flower? Part 2

As promised last week, here is Part 2 of “Why doesn’t my plant flower?”. If any of you know of more reasons that are not listed here or in the previous week’s blog, please let me know. Happy gardening!

There may be several reasons why a landscape plant does not flower (see last week for more reasons):

Over fertilization caused leaf burn on Liriope spicata — Over fertilization caused leaf burn on creeping lilyturf (*Liriope spicata*)

1) Over fertilization may inhibit flowering.

Do not fertilize newly planted trees and shrubs the first 2-3 years after planting
Plants need to put their energy into establishing a healthy root system to support future shoot growth
Once the plant is established (2-3 years), fertilizers may be added if a soil test suggests fertilization is needed
Over fertilization with quick-release, high nitrogen (N) fertilizers can lead to excessive leaf growth at the expense of flower bud development
Avoid using lawn fertilizers around the base of your plants, as they are often high in nitrogen
More is not better; follow all fertilizer label directions and do not add more than is required
Your landscape plants might not even need fertilization, especially if compost is added or the soil conditions are favorable for plant growth

2) Poorly-drained, heavy clay soils can result in leggy, unhealthy looking plants that may not flower or will die.

Azaleas planted in poorly drained, heavy clay soil will not live long

Poor drainage will stunt growth, limit flowering, and may make plants more susceptible to root and crown rot
Before planting, assess soil for drainage
Dig a hole in the soil about 12 in. (30.5 cm) deep and 8-10 in. (20.3-25.4 cm) wide
Fill the hole with water to the top and let it drain for one hour
After an hour, measure the water depth with a ruler and record the new water level from the original level
If the water level drops less than 1 in. (2.5 cm) from the original water filled level, soil drainage is slow
The following day, if water is still in the hole, your soil needs much improvement
Desired range for water drainage is 2 to 6 in. (5.1-15.2 cm) per hour
Drainage can be improved by adding organic matter such as compost, composted leaf mulch, or other organic material; works well prior to planting
If possible, plant in raised planting beds amended with compost, topsoil and other organic amendments to improve drainage and root establishment

3) Under watering can cause a lack of flower buds or poor flower development.

Wilted hydrangea (*Hydrangea* spp.) source http://chatham.ces.ncsu.edu/2014/07/helping-your-yard-survive-drought/

Water immediately after planting for all landscape plants with a hose
Water trees, shrubs and perennials several times a week for the first month or two, depending on weather
Watering may be needed daily especially if windy, dry and hot
Check actual root ball/soil directly where the plants’ roots are located; insert your finger or soil probe as far as it can go
If you feel moisture, the plant may not need additional watering
Plants previously grown in soilless media in containers and bareroot plants require more frequent watering
Do not rely solely on rainfall as the amount may be inadequate to penetrate the root ball
If you see wilting of foliage, the plant is too dry
Plant establishment will take several years or more for trees, slightly less for shrubs and one to two years for herbaceous perennials
After establishment, 1 in. (2.5 cm) of water a week is recommended; check rainfall with rain gauge in yard
Avoid overhead irrigation as this keeps the foliage too wet and may increase foliar diseases
Water at the base of the plant using soaker hoses, drip irrigation or a hose set at a very slow flow rate to allow for percolation into the soil and avoid water runoff

4) Road salt injury can damage or destroy flower and vegetative buds

Winter road salt injury on eastern white pine (Pinus strobus) — Winter road salt injury on eastern white pine (*Pinus strobus*)

Fast-moving traffic and high winds from wet, salted roads accumulate on dormant plants in winter
Sodium chloride (NaCl) is most common deicing salt used and causes the most damage
Most damage occurs within 60-100 ft. from road
Desiccates and may kill buds, twigs; can burn foliage of evergreens; reduces water uptake by roots
Also accumulates on soil surface from melted, salted water from roads
Plant salt tolerant plants near roads, use physical burlap barriers to protect plants, leach soil in spring
Use of anti-transpirants and dormant oil sprays are ineffective in prevention of salt spray injury

5) Insects or diseases may be present which can reduce or eliminate flowering

Shoot death of TINY DANCER™ common lilac (Syringa vulgaris 'Elsdancer') from bacterial blight — Shoot death of TINY DANCER™ common lilac (*Syringa vulgaris* ‘Elsdancer’) from bacterial blight

Oystershell scale on 'Redwine' lilac [Syringa (Villosae Group) 'Redwine'] — Oystershell scale on ‘Redwine’ lilac [*Syringa* (Villosae Group) ‘Redwine’]

Plant is stressed and may not flower; more energy within a plant used for defense
Various bacterial pathogens can kill emerging buds and flower clusters, i.e. bacterial blight
Fungal pathogens can also do the same or reduce the size or quality of the flowers, i.e. powdery mildew, Botrytis
Certain insects, such as borers and scale, weaken a plant so it no longer flowers or flowering is reduced
Treatment for these pests needed or the plant may die
Improve plant health by watering and judicial pruning of infected/infested branches
Do not fertilize at this time as the plant is trying to recover from pests

6) Black walnut (Juglans nigra) and butternut (J. cinerea) trees can kill sensitive plants nearby.

Black walnut (Juglans nigra) tree roots, twigs, leaves and roots all contain juglone that can inhibit or kill nearby plants susceptible to juglone — Black walnut (*Juglans nigra*) tree roots, twigs, leaves, nut hulls and bark all contain juglone that can inhibit or kill nearby plants susceptible to juglone

Both of these trees and to a lesser extent hickories (Carya spp.) excrete juglone, a phytotoxic chemical produced in the leaves, twigs, bark, nut hulls, and particularly in the roots
Not all plants are sensitive to juglone, but those that are sensitive die either quickly (tomatoes, peppers) or over several years
Ornamentals sensitive to juglone include lilacs, crabapples, rhododendrons and azaleas, hydrangeas, etc.
Black walnut tree roots extend far beyond the drip line of a tree
Even if the tree is removed, roots remain in soil and continue to excrete juglone for several years

7) Deer or rabbits may be browsing on the flower buds.

Stems girdled by rabbit feeding on stems of burningbush (Euonymus alatus) — Stems girdled by rabbits feeding on stems of burningbush (*Euonymus alatus*)

During winter, deer and rabbits like to feed on the twigs, bark, and flower buds of many plants
Once the flower buds are destroyed, have to wait another year for flower bud set unless the plant flowers later in summer
Plants resistant to deer and rabbits are available, but if hungry enough, they will eat most any plant
Rabbits and voles chew on bark of shrubs and trees causing girdling of twigs or major stems/trunk
Girdled stems may die or barely flower or leaf out
Damaged branches should be pruned back to live wood

Laura Jull, Ph.D. aka The Lorax

Corny Ancestry

I love growing weird plants, and I’m endlessly fascinated by plant breeding and the extreme transformations humans have made in our crop plants over the history of agriculture.

Which is why growing teosinte, the wild ancestor of corn, was a no brainer. Even before I planted it, comparing the seeds is fascinating. teocornseed

Once growing you can see the similarity. Teosinte is on the left in the picture below, corn on the right.

The most dramatic difference between the two, I think, is the “ear” of teosinte, which is nothing more than a thin sprig of half-a-dozen seeds.

It is amazing to me that native Americans in Southern Mexico, with no knowledge of genetics, were able to transform this grass with a handful of tiny, rock-hard seeds into one of the single most productive crops in the world.

Perennial Funday: Rudbeckia grandiflora ‘Sundance’

Just back from the always-inspirational Perennial Plant Association Symposium, this year held in Baltimore. The theme celebrated the massive influence of German plantsmen and designers on both the mid-Atlantic and the perennial business as a whole. Whether a grower, garden center owner, or landscape designer, the names historically associated with Mid-Atlantic horticulture – Kurt Bluemel, Oehme, van Sweden & Associates, etc. – resonated with all attendees.

The history of the “perennials movement” was recounted – where the Germans (and more than a few Dutch) admired, utilized, and selected cultivars of our fabulous summer and fall-blooming native perennials – long before we North Americans ceased relegating them to ditch weeds. And then they taught us how to use them in “New American Garden” style – sweeping herbaceous plantings (fewer species but larger quantities of each), mixed with ornamental grasses and non-native but pollinator-friendly beauties such as Salvia nemorosa and Perovskia atriplicifolia.

'Sundance' massed with Rudbeckia triloba 'Prairie Glow' in the Bluemel garden. — Rudbeckia grandiflora ‘Sundance’ massed with Rudbeckia triloba ‘Prairie Glow’ in the Bluemel garden.

But this was my first encounter with Rudbeckia grandiflora ‘Sundance’. This seed strain was introduced by Jelitto® Staudensamen seven or eight years ago. It has a pretty broad native range… Midwest to South-Central United States. USDA cold hardiness zone ratings listed as 5-8 and 4-9 from various sources. Always full sun. Didn’t see a speck of powdery mildew.

The flower habit is a bit like Ratibida pinnata – the slightly drooping petals give the sensation of movement (even with zero breeze, 90% humidity, and 96° F). The clear yellow color works with just about anything. Around 4’ tall, the sturdy stems showed little sign of flopping. I’m sure the cones will persist, adding texture as the fall progresses.

'Sundance' in action at Emory Knoll Farms. — ‘Sundance’ in action at Emory Knoll Farms.

‘Sundance’ will never impress in a nursery container in May. It’s one of those you-must-see-it-in-the-garden plants. OR or you can take my word for it. And that word is “Yowza!” (Followed by “gimme gimme gimme.”)

Hey, Consumer Reports Wrote Back! And Yes, They Are Comfortable Recommending Useless Chemicals That Might Cause Cancer!

Two weeks ago I wrote an open letter to Consumer Reports voicing my concerns about some recent articles they had published regarding lawn and garden care, as well as reiterating some issues that Linda Chalker-Scott Ph.D. had with one of their stories. You can read the article for yourself, but the long and short of it is that they made some weed control recommendations that don’t work and recommended a chemical which might cause cancer. Honestly, I fully expected my post to be ignored, but you guys grabbed onto it and posted it over on the Consumer Reports Facebook page and, amazingly enough, they wrote back to me that night and told me they’d get back to me!

Man, was I excited, because hey, even though I’m no longer with a University Extension Service I still have that “impact” mentality. I was looking forward to Consumer Reports writing a little letter in the front of the magazine saying that their recommendation was faulty and that they would do better in the future. Or at least I was expecting them to write me a little note saying hey, we were wrong, and in the future they’ll do better. Look, I’ve worked with pesticides and plants for over 20 years, and to have the chance to influence Consumers Reports, a magazine whose integrity I’ve respected for years…. and maybe even help them see where they’d gone wrong and improve their future recommendations?…Wow…This was a dream come true!

After a week I was getting a little antsy, but they wrote back again, told me some people were on vacation delaying their response, and I’d get something soon.

Then last Thursday they sent me the letter which I have included at the end of this post. It was totally worth the wait!

The first thing I noticed was that Linda Chalker-Scott had somehow lost her Ph.D.. I think I speak for most Ph.D.s when I say that it isn’t a big deal if you don’t include our degree when you write to us, but if you write a letter to two Ph.D.s and include the Ph.D. for one and not the other it’s a little weird, especially if the Ph.D.s are a man and a woman and the man gets the Ph.D. and the woman doesn’t. But I quickly got over any insult I felt for Linda because hey, they misspelled my name. Linda and I have both been insulted before, but to insult us both before even starting the body of the letter?

That’s pretty special!

Now I knew I was in for a good read!

In our letters Linda and I voiced concerns about the efficacy of the treatments that Consumer Reports was offering. With that in mind I provided in my letter my name and a few of my credentials demonstrating that I had some idea of what I was talking about when it came to weed control. Consumer Reports obviously took this very seriously and when they wrote back to me they provided the names of the organizations they contacted for information including “experts from the Beyond Pesticides and the Great Healthy Yard Project”. The experts themselves went unnamed.

Though unnamed, they did provide the credentials of the experts from these organizations, namely that they were “two groups we’ve consulted in the past.” Wow, impressive.

Let me be clear here, these are two fine organizations with worthy goals and good people, but do they have people on staff whose horticultural knowledge approaches the two Ph.D.s and decades of experience that Linda and I have? If they do then please let us know. There’s a comment section below.

Our degrees and experience don’t automatically make us right, but they do suggest that we deserve to be taken seriously. Specifically, if we tell someone that wiping clove oil on a cut stump won’t kill kudzu or barberry then guess what? IT ISN’T LIKELY TO KILL KUDZU OR BARBERRY. It is not a matter of speed or repeated applications as you infer in your letter. If Consumer Reports doubts the information that Linda or I provide then it would be appropriate for them to contact some other experts with legitimate credentials – regardless of whether they are members of “groups we’ve consulted in the past” or not. Or they could try it themselves. Shoot, this is Consumer Reports we’re talking about. They’re supposed to test everything!

To take this a step further, if Consumer Reports were looking for credentialed experts then why didn’t they contact Extension personnel from their favorite state university? Sure, they consulted some extension articles but, based on what was written, I’m not sure they understood what they read. For example, I looked all over and nowhere could I find a University of Minnesota publication suggesting that “going over the lawn with a core aerator might eradicate [dandelions]”. Eradication is a strong word that isn’t usually associated with aeration and, unless they can demonstrate otherwise, I think it likely they’re either misunderstanding or misrepresenting what they read.

Actually, this part of Consumer Reports letter was kind of funny because they called it “the University of Minnesota extension”. That’s kind of like saying “the University of Minnesota music” or “the University of Minnesota botanical”. It should be “the University of Minnesota Extension Service”. But I’m being petty.

Now to the heart of the letter, and my greatest concern since it deals directly with Consumer Reports status as an advocate for consumers.

I am no fan of any pesticide, but I am especially concerned about organic pesticides because, as natural products, consumers often assume that they are necessarily safe. The clove oil recommended to kill the cut stumps of certain plants in the original article is a perfect example. This was a great opportunity for Consumer Reports to demonstrate that natural does not necessarily mean safe. Instead Consumer Reports defended their position stating, simply, that they consider clove oil to be a safer alternative to Round-up. For anyone concerned about the safety of their family I’m sure it’s comforting to know that the precipice they’re hanging over by using clove oil is 50 feet rather than 300.

To summarize why I feel they’re making a mistake in taking eugenol so lightly you can view the blog post I made previously and follow those links (To summarize, it offers a study where tumor incidence increased in mice exposed to eugenol and shows that the Registry of Toxic Effects of Chemical Substances lists this compound as a carcinogen). And, just for fun, here are some additional sources that demonstrate that eugenol may have some serious potential to be hazardous to one’s health.

It has been found to be a potential mutagen

It has been shown to cause chromosomal aberrations in hamster embryo cells

It has shown some level of genotoxicity

It is quite cytotoxic to skin cells even at low levels

Here’s another poisoning besides the one I offered in my last letter

And another

These poisonings are only a few of the ones listed in the literature – you can find more, and you can bet that there’s even more that have occurred which simply didn’t get written up.

Wait! Wait! I’ve gone too far! Consumer reports did say in their letter that they would include a section which states that: “we will note in the future that the oil can be dangerous if ingested.” That’s great, especially considering the cytotoxicity that this chemical has to human skin cells (see the article above).

I know I feel a lot safer now.

And the crazy thing here is that anyone using clove oil as suggested by Consumer Reports is subjecting their family to a danger that isn’t even necessary – because clove oil won’t even be effective for many of the purposes for which it was recommended!

There’s a lot more to the letter below than what I’ve listed here, but this post is getting way too long. Please feel free to read and comment as you see fit. I will not be renewing my subscription to Consumer Reports this year. I do not necessarily encourage you to do the same, but I do encourage you to let them know how you feel on their facebook page or otherwise. If you don’t, things will not change.

I recently read that there was a brain drain at Consumer Reports, I dearly hope that this is not true.

If Consumer Reports really wants to advocate for consumers, then let’s hold them to it.

Jeff Gillman

Here’s the letter:

Dear Linda Chalker-Scott and Jeff Gilman Ph. D. (cc Garden Professors),

Thank you again for your responses to our article “Beat Those Weeds,” which first appeared in the June 2015 issue of Consumer Reports. Though our advice was aimed at homeowners, we appreciate this opportunity to engage with the professional gardening community, and we welcome any additional insights you have into the issue of sustainable lawn and garden care.

Our goal was to introduce homeowners to non-toxic forms of weed treatment. As we noted in the article, the average yard contains 10 times more chemicals per acre than a typical commercial farm, according to the U.S. Fish and Wildlife Service. The article also alerted readers to the fact that the International Agency for Research on Cancer, a division of the World Health Organization, had recently designated glyphosate (the active ingredient in herbicides like Roundup) as a probable carcinogen.

In developing our list of alternative weed treatments, we worked with experts from the Beyond Pesticides and the Great Healthy Yard Project, two groups we’ve consulted in the past. We also referenced numerous cooperative extensions. For example, our point that aerating soil can help control dandelions is supported by the University of Minnesota extension (on whose faculty we understand you served, Dr. Gilman), while the statement about Canadian thistle being common in vegetable gardens with peas and beans came from the Penn State extension.

As you know, lawn and garden care often involves a lot of trial and error, and there’s no shortage of controversy surrounding certain techniques (for years we’ve said corn-gluten meal can be an effective natural pre-emergent herbicide, though we know there are those who disagree). It’s also true that “home remedies” usually aren’t as aggressive as chemical treatments. We tried to make this clear by telling readers that repeat applications would probably be necessary with certain methods, though perhaps we could have stated the fact more clearly. Again, our principal goal was to offer safe treatments, not necessarily those that deliver the fastest results.

That takes us to your point about clove oil, which we offered up as an effective treatment for barberry and kudzu. You note that its main ingredient, eugenol, is classified as a carcinogen by the Registry of Toxic Effects of Chemical Substances. You also reference a case in which a 2-year-old child nearly died after drinking between 5 and 10 ml of clove oil.

We would certainly agree that clove oil should not be ingested. However, we would also note that, according to the World Health Organization’s International Agency for Research on Cancer (WHO IARC), eugenol is classified as Group 3, where there is limited evidence for carcinogenicity from experimental animal studies. Glyphosate, on the other hand, was recently classified by the same agency, WHO IARC, as Group 2A, a probable carcinogenic to humans, due to limited evidence of carcinogenicity in humans for non-Hodgkin lymphoma from agricultural exposure studies and sufficient evidence of carcinogenicity from experimental animal studies. So relatively speaking, we feel strongly that clove oil is a safer alternative to Roundup. However, we will note in the future that the oil can be dangerous if ingested.

Moving forward, we will also emphasize the advice you end your letter with—that the most effective, safest, and easiest way to eliminate weeds is to pull or dig them out. On that point, we couldn’t agree more.

Thank you again for your feedback. We look forward to more spirited collaboration and dialogue on future lawn and garden-related content.

Sincerely yours,

Consumer Reports

Joe Diliberti
Corporate Relations Associate, Consumer Reports

Out of the bottle and into the bag

Last week I was having lunch with my mom at our favorite nearby nursery/café. After failing to resist the grilled cheese sandwich (3 cheeses! And buttery panini bread!), we walked off lunch in the garden supply part of the nursery. Normally I’m on my best behavior when I’m shopping with my mom (i.e. I don’t take photos of things I’m going to take to task on the blog). But like the 3-cheese grilled sandwich I was unable to resist the bags of biodynamic compost.

Biodynamic compost is now available at garden centers

Long-time readers of the blog may remember my earlier column and post on biodynamics. Since I wrote the original column over 10 years ago I’ve watched biodynamic marketing move from boutique wines to coffee, tea, tomato sauce…and now to garden products. Really expensive garden products, as in $19.99 for one cubic foot of compost.

An "untapped source of power and majesty" makes this compost different. — An “untapped source of power and majesty” makes this compost different.

What makes this bag of compost worth $19.99? One has to assume it’s the biodynamic preparations used to treat the compost. They’re referred to in the label under “concentrations of yarrow” and so on. Do these preparations make a difference? The label suggests it might be to restore the soil’s vitality. Is there validity to this claim?

It's doubtful that all of these ingredients are locally available. And why are so many materials needed? — It’s doubtful that all of these ingredients are locally available. And why are so many materials needed?

In 2013 I published a review of the scientific literature on biodynamics, specifically looking at whether biodynamic preparations have a measurable impact on anything they’re applied to. In a nutshell, the answer is no. (Though this article is behind a paywall, I can send a pdf to you by email if you’d like to read it.)

Don’t let packaging and magical words sway you. Compost made with local materials like bark or agricultural wastes and certified by the US Composting Council is reasonably priced and sustainable.

James Kennedy on Chemistry

Caffeine_(1)_3D_ball — Caffeine Molecule – Wikipedia

Sometime in the last twenty years or so, the word “chemical” has become a dirty word. Hard to pronounce words. Unnatural synthesized substances. Mad scientist concoctions brewed in a laboratory.

I used to try to introduce some perspective when I facilitated pesticide workshops for the general public by teaching how scientists and regulators determined toxicity, so comparisons between familiar substances, like caffeine, aspirin, or detergents could be made, to varying degrees of success.

It was the “unnatural synthesized substances” part that I had the most difficulty overcoming.

James Kennedy, a chemistry teacher in Australia noticed the same problem, and started a blog and outreach effort, using infographics to illustrate the chemical make up of familiar fruits and vegetables.

In this NY Times piece, he gives the reason why:

As a high-school chemistry teacher, I made these posters for my students as a visual introduction to our organic chemistry course. I want to erode the fear that many people have of ‘chemicals’, and demonstrate that nature evolves compounds, mechanisms and structures far more complicated and unpredictable than anything we can produce in the lab.

The success of the basic chemical makeup posters led further to include the evolutionary history of fruits and vegetables from their wild ancestors, as explained in this Brad Plumer article at Vox.

Fruits and vegetables have changed a lot since the onset of agriculture 10,000 years ago, as generation after generation of farmers artificially bred crops to select for more desirable traits like size and taste.

But that change can be hard to visualize. So James Kennedy, a chemistry teacher in Australia, created some terrific infographics to show just how drastic the evolution has been.

His blog is simply called James Kennedy, and here are all the infographics, which also can be ordered as posters.

Show me the data!

One of my favorite bumper stickers from days gone by said simply “Stop Continental Drift”. Good luck with that.

Today’s topic deals with another type of drift – a phenomenon one of my professors referred at ‘Bibliographic drift’. This type of drift occurs when authors cite a paper without bothering to look up the original source. Then a second author cites original source based on the first author’s paper; then a third author cites it based on the second paper and so on and so forth. This is why grad students learn that second citing is a cardinal sin.

It’s an easy trap to fall into even in the age of access to electronic journals. It can happen in all sorts of ways, especially if the point the author trying to support is something that is intuitively appealing and not likely to be questioned. For example, I was recently reading through The Practical Science of Planting Trees by Gary Watson and E.B. Himelick. It’s a good book with lots of great info and photos but under the section on digging the planting hole there is a subsection “wider is better”. This is something we all ‘know’ but there is no data with any scientific rigor to support it; at least not that I’ve ever been able to find and I’ve looked repeatedly. So I was intrigued to see Watson and Himelick cite four papers to support the notion that wider is better. Cool. So I went through the bibliography to look up the citations.

Can you dig it? My former research technician Dana Ellison installs a tree in Detroit.

First up, Arnold and Welsh 1995. Effects of planting hole configuration and soil type on transplant establishment of container-grown live oak. J. of Arboriculture 24:213-218. This paper doesn’t even discus planting hole width, at least not directly. The authors looked at various planting hole configurations (round, square, star-shaped) but made a point to keep the planting hole volume the same. Zero points for wider is better.

Next, Corley 1984. Soil amendments at planting J. Environ. Hort. 2:27-30. One of the experiments in this paper compared root and shoot growth of four shrub species transplanted from #1 containers into holes that were with 1.75x or 3.5x the width of the root-ball. The author measured root and shoot growth after two years and the results were a mixed bag. They found the wider hole was better about half the time, the other half of the time it didn’t make a difference. One point for wider is better (sort of).

Next, Montegue et al. 2007. Influence of irrigation volume and mulch on establishment of select shrub species Arboriculture & Urban Forestry. 33:202–209. The title of the paper says it all; the authors compared water relations and growth in response to mulch and irrigation but planting hole size wasn’t included as a variable. (Spoiler alert: mulch improved growth and water relations). Zero points.

Last and most interesting, Watson et al. 1992. The effect of backfill soil texture and planting hole shape on root regeneration of transplanted green ash. J. of Arboriculture 18:130-135. In this study the authors looked at new root growth and shoot and diameter growth for three years after transplanting green ash trees into planting holes that were 1.2x, 2x, or 3x the width of the root ball. And they found… nothing. Well, not nothing but they didn’t find any effects of planting hole size on root density, shoot growth or caliper growth. To help visualize the response I’ve summarized their growth data three years after transplanting below. One point for it doesn’t matter.

Cumulative growth response of green ash trees to planting hole width 3 years after transplanting. adapted from Watson wt al. 1992

As a final note I include a photo from the Waston et al. paper 1992. The photo is fuzzy but the caption should be clear.

So where does that leave us? Digging a wider hole doesn’t hurt, except maybe your back. And I think that’s part of the appeal of this advice: If it’s more work it must be better. Dig a hole 2 times, 3 times, 10 times the width of the root-ball if you want. Just don’t say “Research shows wider is better…” because it’s ambiguous at best.