Author: Linda Chalker-Scott

Dr. Linda Chalker-Scott has a Ph.D. in Horticulture from Oregon State University and is an ISA certified arborist and an ASCA consulting arborist. She is WSU’s Extension Urban Horticulturist and a Professor in the Department of Horticulture, and holds two affiliate associate professor positions at University of Washington. She conducts research in applied plant and soil sciences, publishing the results in scientific articles and university Extension fact sheets. Linda also is the award-winning author of five books: the horticultural myth-busting The Informed Gardener (2008) and The Informed Gardener Blooms Again (2010) from the University of Washington Press and Sustainable Landscapes and Gardens: Good Science – Practical Application (2009) from GFG Publishing, Inc., and How Plants Work: The Science Behind the Amazing Things Plants Do from Timber Press (2015). Her latest effort is an update of Art Kruckeberg’s Gardening with Native Plants of the Pacific Northwest from UW Press (2019). In 2018 Linda was featured in a video series – The Science of Gardening – produced by The Great Courses. She also is one of the Garden Professors – a group of academic colleagues who educate and entertain through their blog and Facebook pages. Linda’s contribution to gardeners was recognized in 2017 by the Association for Garden Communicators as the first recipient of their Cynthia Westcott Scientific Writing Award. "The Garden Professors" Facebook page - www.facebook.com/TheGardenProfessors "The Garden Professors" Facebook group - www.facebook.com/groups/GardenProfessors Books: http://www.sustainablelandscapesandgardens.com

Do your homework before hiring landscape help!

(A guest post by Rich Guggenheim. You can see Rich’s bio at the end of this post.)

When it comes to shopping, my friends all know it takes me a long time to make a decision. I methodically research out what I want. Then I narrow it down to a few items. After I look over my choices carefully, I may go home to get on the internet and look at consumer reviews; I may go from store to store and check out prices. I look for quality and I look to make sure I am getting a product that is worth the money I am spending on it. I want to make sure my investment will last. Sometimes, my shopping experience will last hours, days, or in the case of a car or computer, it could be months.

My yard is no different. When I need yard work done, such as lawn aeration or tree trimming, I am insistent on high quality work. As a homeowner you are the first and the last line of defense when it comes to making sure that a quality job is done, and done correctly! Knowing what to expect in landscape maintenance and being armed with a small amount of knowledge as a consumer can play in your favor.

Always hire a certified professional to do your work. Would you seek medical advice from an individual who was not licensed to practice medicine? Of course not! Why then would you do it with your yard? I recommend that you check into the individual or company before hiring them. Do some homework. How have they been trained? Where is their certification from? Are they insured, licensed, and can they provide you documentation? Are they registered with the Better Business Bureau? If so, what is their rating? Drive around and check on some of their previous work. Is it the kind of quality you would want in your own yard? Ask for references. Ask questions! This is, after all, a job interview for the contractor. Just because they are the cheapest does not mean they should get the job, and just because they slap a business magnet on the side of their pick-up truck does not mean they know what they are doing! In the following I will be talking with you about what to look for when hiring a contractor to do yard work and how certain procedures should be done. Armed with this knowledge, you will be better able to ensure the work done in your yard is of the quality you deserve for the money you pay.

Lawn aeration is perhaps one of the best things that you can do for your lawn. Done twice a year, once in the spring and once in the fall, core aeration combats soil compaction. Soil compaction is a problem in nearly 80% of all landscapes. In addition, aerating your lawn helps combat thatch accumulation and reduces the amount of water you need to apply to your lawn. The reason for this is because when your soil is compacted oxygen and water can’t penetrate into the soil. Fertilizer can’t get penetrate the soil either. As a result, roots are often shallow, and the lawn will need more frequent irrigation. (1, 2, 3, 4)

Core aeration removes small plugs, about 1-3 inches long from the soil. A single aeration using a machine with 1/2-inch diameter tines removes as much as 10 percent of the thatch if enough passes are made to achieve average 2-inch spacing between holes. Remember the key is 2-inch spacing. This may mean that multiple passes on the lawn are required. This small investment of an extra $10 will pay dividends in the end.

What do you do with the cores after you have had the lawn aerated? That really is a personal decision. Some people do not like the little plugs being left on their lawn, although there may be benefits to allowing them to disintegrate into the lawn again.

If you do decide to remove them, they are great for the compost bin. Other options may be to power rake the lawn after aeration, watering, or simply running a lawn mower over the lawn after you aerate (although this practice will cause the blades on your lawn mower to dull). Once you have aerated your lawn if you need to reseed, this is the optimum time to do it. The best part of reseeding now is there is no need to top dress the lawn, as the lawn seeds will have nice little holes in which to germinate!

Another type of aeration being marketed by many lawn care companies these days as a replacement for core aeration is liquid aeration. While different ingredients make up this popular lawn service, the main ingredients seem to be liquid humates (organic matter) and sodium lauryl sulfate (soap). These are nothing more than snake oil remedies and are no substitution for the real deal of removing the plugs from your lawn by core aerating. There is no scientific research which has shown chemical aeration to be effective. You may as well throw dirty dish water out on your lawn. (5)

The thing to remember from all of this is that you want to have your lawn aerated twice a year; in the spring, and again in the fall. The plugs removed should be 2-3 inches long, and on 2 inch centers, which may require multiple passes on your lawn.

Tree pruning is something I take seriously. It is a science which should not be left to a novice and is far more than could be covered in one article. For me, spotting a bad tree pruning job is as easy as spotting a bad haircut. The only difference is a bad hair cut grows back and has no adverse side effects on your health. However, a pruning job can have enormous effects on the health of a tree, either for good, or for bad. When you hire an arborist, make sure they are ISA certified, licensed, and insured. To find an ISA certified arborist, visit their website.

The key points for a good pruning job really come back to structurally pruning the tree correctly when the tree is young. Improper or lack of pruning when the tree is young can greatly increase the likelihood of tree failure when the tree is older. Cuts on branches larger than 4 inches increase the possibility of decay and disease. If possible, prune trees when the branches are smaller than 4 inches in diameter.

When pruning trees, it is important to prune the branch back to the branch collar. Don’t leave stubs, or what I call “hangars” where you can hang your coat. Leaving these nubs will cause decay and disease to move into your tree.

The last key component to pruning is to always remove a smaller branch back to the parent branch, never the other way around. When you remove a parent branch, unless the wood is dead, you greatly increase the risk of beginning the downward spiral of death and decay in the tree. While this is great for less reputable tree-trimming companies who will have to come back year after year to remove an ever-increasing amount of dead wood from the canopy of the tree, it is hard on your pocketbook; more importantly, your tree’s life is shortened! By knowing some pruning basics, you can ensure that you are hiring a professional who knows what they are doing, and will extend the value and life of your landscape.

Carrow, R. N., B. J. Johnson, and R. E. Bums. 1987. Thatch and quality of Tifway bermudagrass turf in relation to fertility and cultivation. Agronomy Journal, 79: 524-530.
Dunn, J. H., D. D. Minner, B. F. Fresenburh, S. S. Bughrara, and C. H. Hohnstrater. 1995. Influence of core aerification, topdressing, and nitrogen on mat, roots, and quality of “Meyer” zoysiagrass. Agronomy Journal, 87: 891-894.
Erusha, K. S., R. C. Shearman, and D. M. Bishop. 1989. Thatch prevention and control. Turfgrass Bulletin, 10(2): 10-11.
Murray, J.J., & Juska, F.V. (1977). Effect of management practices on thatch accumulation, turf quality, and leaf spot damage in common Kentucky bluegrass [Poa pratensis]. Agronomy Journal,(3), 365-369.
Lloyd M. Callahan, William L. Sanders, John M. Parham, Cynthia A. Harper, Lori D. Lester and Ellen R. McDonald.Cultural and chemical controls of thatch and their influence on rootzone nutrients in a bentgrass green.Crop Science, 1998 38: 1: 181-187. doi:10.2135/cropsci1998.0011183X003800010030x

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Rich Guggenheim is a consumer horticulture educator with the University of Idaho in Canyon County and is the program director for the University of Idaho Extension Master Gardener volunteer program. Rich is also working on a Ph.D. in plant pathology. Rich has been an horticulture extension agent for Colorado State University, horticulturalist for Disney Parks, and is the host of the weekly “Avant Gardener” radio program in Boise. He can be reached at richg@uidaho.edu

My New Project — The Plants We Eat

By Jeff Gillman

I love stories, and my favorite stories, as you might guess, are true stories about plants. One of the things that I’m best known for here at the UNC Charlotte Botanical Gardens is telling random stories about some odd tidbit or another to students trapped in my classes or visitors locked into garden tours, but recently I found a new way to share my collection of those eclectic plant stories: Podcasting. Not only do I get to talk about all the things that I love to talk about, only those people who really want to hear about them have to listen. It’s a win-win!

From apples and artichokes to digitalis and peyote, our world is full of amazing plants that we interact with on a daily basis. This greenery can sustain us, intoxicate us, cure us of disease, and even kill us.

I have had the opportunity to read about and work with an incredible variety of plants, but the ones that I find most fascinating are those we ingest as food or medicine, and that’s what this podcast is about. From toxic honey made from Rhododendrons to the incredible photosynthetic efficiency of sugar cane and the natural genetic modification of sweet potatoes there are an incredible number of stories that the plants around us have to tell, but if you’re just interested in growing these plants then we have you covered there too. I am doing these podcasts with a friend of mine, Cindy Proctor, who loves to talk about how to grow these plants, so there’s plenty of that in the podcast as well.

Rhododendron from which Mad Honey is made

So to make a long story short, we would love it if you would take the time to listen to our podcast. You can find it on the podcast app on your iPhone or on Sound Cloud, or here at the Botanical Gardens website.

And since we’re new at this we would love it if you would let us know what you think. You can comment on the blog post here, or on the post on Facebook, or feel free to write to me at jgillman@uncc.edu.

Master Gardeners at a crossroads

{Warning. Today’s post is a rant. So I’ve illustrated it with pretty flowers in soothing colors to make it more palatable.)

Anyone who gardens in the United States will be familiar with Master Gardeners. The Master Gardener program was started by Washington State University in 1971, when Extension agents in the largest urban counties found themselves overwhelmed with questions from the gardening public. These agents proposed training volunteers to help with educational outreach efforts, and with support from the university the first Master Gardener program was born. The history and function of Master Gardeners is further detailed in a couple of articles I co-authored (Chalker-Scott and Collman 2006 and Chalker-Scott and Tinnemore 2009): the more recent article also raises concerns about the decline of programmatic support in Washington state and elsewhere. If you’re a Master Gardener, the repercussions of this should alarm you.

What makes a successful Master Gardener? According to Sharon Collman, the last surviving founding agent of the WSU program, it begins with this:

A commitment to basic and advanced training program;
An open-minded approach to continuing education of themselves as well as others;
A willingness to provide science-based, unbiased information regardless of personal beliefs. (From Chalker-Scott and Collman, 2006)
Pink fawn lily

To be successful, volunteers need high-quality education consistently provided by university discipline experts. And that’s where the model is starting to fail in Washington state. Extension specialists who used to provide training to Master Gardeners in plant pathology, entomology, lawn and turf management, soil sciences, and other important fields have not been replaced by the university when they resign or retire. More and more training is left to the devices of individual counties, whose Extension funding from WSU has been gutted over the decades. The previous university-centric approach to Master Gardener training has devolved into volunteer-driven county programs with little educational oversight.

While counties should be commended for keeping programming alive in the face of crippling budget cuts, the lack of meaningful curricular oversight by the university means that volunteers often don’t get the most current and relevant information pertaining to the science of gardening. Worse, they may be taken in by popular products and practices with no basis in science. Other volunteers may let their personal beliefs interfere with their pledge to provide objective, science-based information on topics including pesticides, GMOs, and other controversial topics. This undermines the credibility of the county program and ultimately the university who claims these volunteers.

If you are a Master Gardener in Washington state or anywhere else in the U.S., it’s really incumbent upon YOU to insist that your land-grant university live up to its public outreach mission. You DESERVE access to Extension faculty specialists whose primary focus is to educate the gardening public. The university takes credit for your volunteer hours when they make reports to the state legislature. Make them earn it.

Don’t waste your time contacting the university – you’ll get nothing but platitudes there. The place for change to start is with your elected state representatives.

Let’s be rational about roots

One of my colleagues alerted me to a blog post on tree myths currently making the rounds on social media. As a myth debunker myself I was particularly intrigued by the last myth “Root Pruning Stimulates Root Branching:”

“When planting a tree’s root ball, It is very tempting to cut back on roots that are circling the ball. It is very often thought that a dense root ball will stimulate new feeder root growth…but that is not the case.

“Don’t worry about encircling roots as they will correct that on a new site.

“Most new root growth occurs at the end of existing roots. Root pruning is often done at the nursery to accommodate packaging and to resume growth before the final sale. If you are planting the tree at its final site, it may be best that you gently break up the root ball but never prune root tips.”

Most surprising of all was the statement at the end of the post which cited an Extension publication by Dr. Ed Gilman at the University of Florida.

Let’s straighten this out (pun intended).

First of all, root pruning DOES stimulate new root growth. It’s just like the response you see when you prune the crown of a plant – the buds below the cut become active and develop into new shoots. There are growing points behind the cut ends of roots which act in the same manner.

Second, circling roots will NOT correct themselves after planting. If they are flexible, you can tease them out to radiate from the trunk. If they are woody, you will have the same luck straightening them as you would in straightening a dowel. If anything, it’s going to break. Not bend.

Seriously. You think this root is going to straighten out?

Finally, root elongation (growth) DOES occur at the end of existing roots – IF they are intact. If they’ve been cut, then we’re back to my first point.

This is basic plant physiology. The response of roots to pruning has been known for several decades. So how could the University of Florida publication be so wrong?

Excessively long roots can easily and safely be pruned before planting

I was able to track down the publication “Dispelling Misperceptions About Trees“. It was written in 1991 and has since been archived – meaning that it’s not considered to be a current source of information any longer. But let’s take a look at what it says, especially the underlined portion:

“Root pruning does not stimulate root branching all the way back to the trunk. Roots are often pruned before moving a tree in hopes of creating a denser root ball.However most root growth after root pruning occurs at the end of the root just behind the root pruning cut, not back toward the trunk. Therefore, dig the root ball of a recently root pruned tree several inches beyond the location of the root pruning. Root pruning should be conducted 6 to 10 weeks before moving the tree. Root pruning more than 10 weeks before moving the tree will reduce the advantages of pruning, because regenerated roots will quickly grow outside of the root ball.”

Root pruning when these trees were dug results in many new flexible roots

This says exactly what I stated in my first point: root pruning stimulates new root growth – which is root branching.

Dr. Gilman’s document goes on to say:

“Roots circling around a container do not continue to grow in a circle once the tree is planted in the landscape. Roots frequently circle within the perimeter of a container several times before the tree is planted into the landscape. The portion of the root which grew in the container does not straighten out, but new growth on this root will not continue to circle.”

So yes! You DO need to worry about those circling roots!

Circling roots turned this crape myrtle into a crap myrtle (Courtesy of Roger Duvall)

In 1991 Ed was an assistant professor at UF and went on to write hundreds of Extension publications and research articles during his career. And in 1991 he was well aware of how root pruning affects root growth.

The moral to this story: read your sources carefully and cite them accurately. And if what you read doesn’t jibe with the current state of science, ask questions!

Notes from the botanical etymology division, toxicology subcommittee

By Charlie Rohwer (Visiting Professor)

The recent assassination attempt England, interesting and significant geopolitically, has reminded me about one of my favorite Latin plant names. A report on the radio stated that atropine therapy is used to treat the specific poison involved in the attempt. To paraphrase Dr. Randy Pausch, “I’m a doctor, but not the kind who helps people.” Therefore, I have no authority on the medical uses of atropine. The world Health Organization lists it as a preoperative anesthetic on its list of essential medicines, so it must be pretty important.

Atropa belladonna, Leipzig botanical garden

But I do like horticulture and I like words. That’s where my interests lie in relation to this story. Many medicines are or have been plant-based. Atropine itself comes from certain plants in the nightshade family. Like any chemical people use, dosage of atropine determines its effects; atropine can be medically useful, or it can be deadly. The drug is named after a specific plant from which atropine can be obtained, Atropa belladonna. The omnibotanist Linnaeus named it in 1753 (can someone come up with a better word for him than ‘omnibotanist?’).

‘Belladonna,’ as it’s commonly called, is a small shrub native to Europe and Asia. ‘Belladonna’ comes from the Italian words ‘bella’ and ‘donna,’ meaning ‘beautiful woman.’ An extract from the plant was applied topically to eyes during the Renaissance to dilate pupils. One sign of sexual arousal is dilated pupils, so the extract would cause a response that looked like sexual arousal. If you were a lady going to a fancy party during the Renaissance and you wanted to look beautiful, belladonna may have helped (according to beauty standards of the time). My optometrist told me atropine isn’t used for retinal exams today because its effects last too long.

The other common name for Atropa belladonna is ‘deadly nightshade.’ The drug, atropine, is made of two isomers of hyoscyamine, made by the plant (and some other related plants). At some doses, hyoscyamine causes muscles to relax (like the iris, for example) due to its effects on nerves that control muscles. At larger doses, it can kill because you need muscles to breathe and to pump blood at a reasonable rate. Dosage and route of entry are important!

The author with one of his favorite books.

So Atropa belladonna was used to make ladies beautiful, hence the epithet ‘belladonna.’ But what about ‘Atropa?’ What’s that mean? Where does the drug atropine ultimately get its name? My favorite book as a kid was “D’Aulaires’ Book of Greek Myths.” Linneaus borrowed from the Greek myth of the three Fates in order to name deadly nightshade. According to D’Aulaires, these goddesses of destiny “…knew the past and the future, and even Zeus had no power to sway their decisions.” Nobody can escape fate. The three fates were named Clotho, Lachesis, and Atropos. The fates are responsible for the thread of everybody’s life. Clotho spins the thread at birth, Lachesis measures it out and determines destiny (what’s on the thread and how long it is), and Atropos (‘inflexible’ or ‘unturnable’) cuts the thread after Lachesis has apportioned it. Atropos is the goddess directly responsible for the end of everyone’s thread of life, and her action is final.

Atropa belladonna simultaneously means something like ‘inevitable, inflexible death’ AND ‘beautiful lady.’ Indeed, the dose makes the poison.

Hello Again, and a fun article that was called to my attention.

By Jeff Gillman (posted by Linda C-S, who has taken liberties with using photos from UNC Charlotte gardens that have nothing to do with Jeff’s post.)

It has been almost two years since I have had the chance to post anything as a Garden Professor. Since then I’ve taken a job as the Director of UNC Charlotte Botanical Gardens and there are all kinds of things I’d like to share with you, and perhaps sometime over the next few weeks and months I will, but for now what is probably most pertinent is that I absolutely love my job. I am still doing some work on garden myths, but what I’m finding more entertaining is investigating the histories of different plants and their interactions with humans. In fact, in about a month or so, my friend Cindy Proctor and I will be releasing a podcast titled The Plants We Eat that investigates the interesting history, culture and biology of the various plants we use for food. We’ve already recorded shows on strawberries, grapes and mad honey, and we’ll be doing shows on apples, figs, and a few others before we release it – we want to have a decent backlog of shows so that we can maintain a pace of one podcast a week.

But enough about me! The current Gardens Professors called my attention to a recent article titled “The effect of ad hominem attacks on the evaluation of claims promoted by scientists”, and I found it informative to say the least. This article provides instructions on how to stop people from trusting a particular study.

No, seriously. If you wanted to you could actually rewrite this as a short manual on how to make people question the results of any scientific study.

And if you did I think it would look kind of like this:

(Short Disclaimer – I’m pretty sure that the authors of the above article never intended it to be taken in the way I’m presenting it. I’m posting this purely as satire.)

So, someone has published a scientific article that you disagree with. Hey, we’ve all been there. Scientific evidence that contradicts your beliefs/works/preconceived notions sucks, but it isn’t the end of the world. There are things you can do.

You might consider conducting your own well-designed experiments that would call into question some of the claims of the offending work. Once upon a time this was been the standard way to address this kind of problem, but this could take months or even years to accomplish. And the truth of the matter is that your experiment might not even say what you want it to and even if it does, with attention spans the way they are, nobody will even remember what you’re even talking about when your paper comes out.

Which is to say, there are better, faster ways to take care of inconvenient research, and that’s where this convenient manual comes into play.

First, realize that attacking the research itself isn’t a sure thing. Sure, it’s the right thing to do, but morals be damned, attacking the research itself can be waaaayyy too technical. People won’t understand what you’re talking about, so forget about it.

Attacking researchers personally by making nasty comments about where they graduated from college or that they do sloppy research would seem like winner, that kind of attack just doesn’t cut it today. Maybe it’s the political climate, but, to their credit, people just aren’t responding to non-specific personal attacks the way they once did.

So you’ve got to be smart and hit them where it hurts. You could say that data was fabricated in the paper that you want to discredit, but this could be problematic if it isn’t true. Not to worry. All you really need to do is find an instance where the researcher did do something wrong. In fact, it’s possible that some past misconduct could be even more effective at discrediting a paper than misconduct on the paper in question itself.

The gold standard, however, is conflict of interest. By establishing that the researcher who has caused you grief has some sort of conflict of interest you can cause people to question the results of research just about as effectively as if some sort of misconduct had taken place, and conflicts of interest are much easier to find! You could blame a company, a person, or even a University. Shoot, want to show that a study, which demonstrates that an herbicide is effective at controlling a weed, isn’t true? All you need to do is show that the company which makes the herbicide gave a few hundred dollars to an athletic program at the school, or show that one of the student workers in the lab has a second cousin employed by the company. It’s all good.

And so there you have it. The fast, easy way to discredit someone. And remember, just implying things can be as effective as having facts. No need to lie! Good Luck, and remember The Truth is What You Make It!

Cryptic cladophylls – stems hiding in plain sight

One of my favorite topics back when I taught Botany 101 was plant oddities. A recent question on our Garden Professors’ discussion group on Facebook reminded me about cladophylls, like the one pictured below.

Cladophyll literally means “branch leaf.” Anatomically it’s a branch (it has nodes from which new stems, leaves, flowers, and even roots can arise), but it functions as a leaf. It’s the main site of photosynthesis in plants such as holiday cacti (Schlumbergera species). Like other cacti, they have reduced leaves and if you look closely at the photo, you can see the leaves as tiny hairs arising from the nodes at the end of the stem and along the sides.

But unlike cacti, these plants aren’t found in deserts, and their leaves are soft threads rather than the vicious sharp spines you’ll find in typical cacti. Instead, these are generally epiphytes in coastal mountains where humidity is relatively high. But root water is limited for epiphytes and these waxy cladophylls probably are adaptations against water loss. Their reduced leaves are immune to drought stress, unlike those of other succulents which appear only when water is plentiful.

Euphorb leaves will drop when water is unavailable

As you might expect from their red, tubular flowers, holiday cacti are pollinated by hummingbirds in their native environment. Gardeners who have a sufficiently mild climate to grow these outdoors might be lucky enough to see them visited.

What’s in YOUR honey? It may not be the nectar you expected.

This month’s National Geographic has a brief article from an ongoing study of the DNA profiles of urban honey. While we can all observe honeybees visiting flowers in our own gardens, until recently we could only assume what nectar they were collecting for honey production. This tantalizing snippet completely blew me away.

The study, undertaken by an entomologist who founded the Urban Beekeeping Laboratory and Bee Sanctuary, is sampling urban hives from major cities, including Boston, Portland (OR), New York, San Francisco, Seattle, and Washington DC. For each of these cities, National Geographic reports the top three plants for honeybees based on relative DNA levels.

Here’s what I found amazing about this research:

- - The top sugar sources are from TREES. Not wildflowers. We don’t see bees visiting trees as easily as we see them visiting flowers, so our perceptions are biased. Over 75% of the sugar used for urban honey is from trees.
    Honeybee visiting flowering tree
  - The trees that are most popular for bee visitation are not necessarily native to those regions. Seattle bees, for instance, prefer linden and cypress trees, neither of which are part of the native coniferous forest. Likewise, the despised eucalyptus trees of San Francisco are one of the top three sugar sources.
    Flowers and leaves of linden
- You’ll notice that I didn’t use the word “nectar” in describing what bees are collecting. That’s because much of the sugar they are gleaning isn’t coming from flowers. It’s coming from sap-sucking insects like aphids that produce honeydew. Bees apparently collect honeydew as well as floral nectar.
  Aphids!
- Urban areas usually have higher plant diversity than rural areas, given the variety of woody and herbaceous plants that people use in their gardens and landscapes. The researchers speculate that this higher plant diversity may be one reason that urban hives are healthier and more productive than rural ones.
  Garden beehive

Many gardeners operate under the assumption that native plants are the best choice for gardens and landscapes. Though certain landscapes (like those undergoing ecological restoration) should only be planted with natives, there is no evidence-based reason that we shouldn’t be using non-invasive, introduced species as part of our planting palette. In fact, research has demonstrated that tree species nativity plays only a minor role in urban landscape biodiversity: most animals learn to use new resources in their environment. Honeybees, considered to be “super-generalists” insects, are demonstrating that in spades.

Our New Year’s Resolution – to keep you informed and entertained every week.

Happy New Year!

The Garden Professor’s collective resolution is to have at least one new blog post a week for 2018. So I’m kicking things off with a little fact checking on the claims made for a product that’s “a complete ecosystem in a bottle.” The company touts its strong connection to science (“our products revolve around biology”). There is a long list of ingredients and claims – way too much for one post. We’ll start with the first four this week.

All this can be yours if the price is right!

Ingredient claim #1: “Chitin/chitin degrading Bacillus: Chitin is a natural polymer that is found in crustaceans, such as crabs, lobsters, shrimp and oysters as well as other organisms, such as insects, worms and fungi. When added to the soil ecosystem, chitin (also referred to as chitosan) promotes the growth of chitin-degrading bacteria. These bacteria, in turn, create a hostile environment for pathogenic fungi and parasitic nematodes. Chitin also acts directly on plants to promote tissue repair and disease resistance.”

Fact check #1: A couple of technical points: oysters don’t have chitin. And they’re not crustaceans. They are MOLLUSKS. They have shells with CALCIUM. And chitosan is not the same thing as chitin. It’s an industrially produced material that comes from chitin.

Chitin is indeed found in arthropods, which include crustaceans and insects. Now, most of us don’t have crabs, lobsters and shrimp roaming our landscape, but we do have insects. Lots of them. They produce a lot of chitin when they molt and when they die. Do you really think we need to add more chitin for Bacillus to consumer? I sure haven’t seen any science supporting that practice.

What about the Bacillus species that degrade chitin? Well, if you’ve got insects in your landscape, you can bet you’ve got microbes that break down chitin as well. Otherwise you’d be up to your garden boots in chitin carcasses. So why do we need to add more bacteria?

Imagine billions of these in your garden…

Finally, there’s no evidence that chitin applied to plants in the landscape has any effect whatsoever. You might get responses in the lab, and chitosan (not chitin) might have some direct application. But like many other elicitors, you have to get it inside the plant to have a cellular effect. And plants are particularly adept at keeping things like decomposing bug bits outside of their tissues.

Ingredient claim #2: “Compost tea: The disease suppressive characteristics of compost have long been known and therefore the liquid extracts from compost, known as compost teas are being use to battle plant disease while stimulating plant growth. Beneficial organisms including bacteria (primarily from the genera Bacillus, Pseudomonas, and Penicillium) along with some yeast and fungi form a physical barrier against disease causing agents and provide a competitive environment in which the pathogenic species lose out. In addition, compost teas stimulate plant growth, translating into a healthier plant, which is more resistant to attack from disease. Compost teas have shown effectiveness in the control of late blight, grey mold, downy and powdery mildew, fusarium wilt, and apple scab among many others.”

The visuals are more interesting than the product.

Fact check #2. Just because compost has disease suppressing characteristics doesn’t mean that water leaching through it will have the same. We’ve been hearing for years that compost tea suppresses disease. Where’s the definitive research? It’s a topic I’ve been following for nearly two decades and there’s still nothing that’s consistently effective. (Another technical point here: it’s illegal to make pesticidal claims of a product that’s not registered for that use. Company lawyers may want to review that.)

There are many species of bacteria, including the ones mentioned, that form protective and beneficial biofilms on plant tissues such as fine roots. You can find these bacteria in compost and other sources of organic material – that’s their food source. You won’t find many of them in compost tea.

I’d love to see evidence of anything stimulating plant growth other than plant growth regulators (or hormones as they’re sometimes called).

Aren’t marketers getting tired of compost teas yet? I’m getting tired of hearing about them. I reviewed the science about them 10 years ago and haven’t seen anything to warrant an update.

Ingredient claim #3: “Essential oils: or essences they are called, are highly concentrated substances extracted from various parts of aromatic plants and trees. Essential oils are combined with other carrier oils and teas for stabilization. Essential oils are used against plant pests and disease by interfering with their reproduction and feeding habits while protecting beneficial predatory organisms.”

Fact check #3: Essential oils have no documented benefit when applied outdoors. They can be effective in closed spaces, like homes and greenhouses, but they dissipate quickly outside. What I really want to see, however, is the mechanism by which oils can identify – and actually protect! – beneficial insects while killing pests. (Hey, lawyers…we’ve got another pesticidal claim here…)

Ingredient claim #4: “Streptomyces griseoviridis: Is a naturally occurring soil bacteria. The microbe deprives pathogenic fungi of living space and nourishment by colonizing roots in advance of fungi. In addition the microbe secretes various enzymes and metabolites which inhibit pathogenic growth. Streptomyces griseoviridis has been shown to promote the growth and yield of all plants. Streptomyces griseoviridis is used for the prevention of root and stem rot, Pythium, Rhizoctonia, Helminthosporium, Sclerotinia, among others.”

All those stickers keep the bad guys from colonizing.

Fact check #4: While this is a naturally occurring soil bacterium, it’s not clear where it naturally occurs. EPA information states it was first isolated in Finland from peat bogs. Is this something we should be introducing to our own soils? Its effectiveness in disease control and plant performance is sporadic and confined primarily to greenhouse application on crop plants. The diseases listed are common in greenhouses, but not necessarily in gardens and landscapes (presumably because there are natural controls outdoors in healthy soils). There is certainly nothing to support its use in gardens and landscapes, especially considering that many native, beneficial bacterial species can colonize plant roots and act as a protective biofilm.

Stay tuned for next time!

“Mulch Murder” Misinformation

This weekend I received a link to a Maryland gardening column with the intriguing title “Murder by Mulch.” My correspondent was concerned that her planned use of arborist wood chip mulch was going to cause problems. I assured her that it would not – but then spent some time looking at the column and putting it through CRAP analysis (credibility, relevance, accuracy, and purpose). It’s a skill that I encourage everyone – not just gardeners – to develop. (You’ll need to read the linked column to understand the context of my comments below.)

So we’ll start with credibility. The column is not a peer-reviewed resource, but then again neither is this blog. The author is a retired Extension specialist with research publications in compost science. That would seem to fit well with the topic. We’ll give it the benefit of doubt for now.

Use of arborist wood chips in a home landscape

How about relevance? Is this information relevant to the use of mulches in home landscapes? Absolutely.

Is this accurate information? At this point the column starts to fall apart. Let’s start with the photo (you’ll need to go to the linked column to see it). This tree didn’t die because of mulch, but because it had girdling roots – the result of planting trees improperly. Furthermore, there is no mechanism I can think of in which mulch would “strangle” a tree.

Next, there is no distinction made among different types of mulch. Bark is not the same as wood chips, and coarse materials function differently than fine mulches. Bark mulches don’t absorb water like wood chips do, and fine mulches inhibit air and water movement into the soil (coarse mulches don’t cause this problem).

Wood chip mulches are an excellent choice for weed control and woody plant establishment

Finally, there is the statement that repeated application of bark will raise soil pH and increase manganese levels. There is no research I could find to support either one of these claims.

The purpose of this column was to educate – but it has failed to do so for the reasons outlined above. Where did the CRAP analysis fall apart?

We need to go back to looking at the author’s credentials. It’s not apparent from his publication record that he’s researched mulches at all. His work was primarily on composts, with the most recent article published in 1998. Nor has he published articles relevant to management of woody plants.

Urban horticulture and arboriculture are relatively new fields of study that are rapidly evolving. Information once accepted as factual decades ago may no longer hold true, as newer research changes our understanding of the way that plants and soils work in managed landscapes.