Be a skeptic – The Garden Professors™

The Dirty Truth Behind the “Dirty Dozen”

By: Abi Saeed

Pesticide residues and risk assessments have been a major topic of interest and inquiry for me for over a decade, and something that I wanted to write about on the Blog for quite some time. Over the past couple of months, I have had several inquiries from people regarding the “Dirty Dozen” list, so I thought this was the perfect time to organize the evidence-based data on this topic. To see a prior post on this topic, you should also check out Jeff Gillman’s post on the Dirty Dozen from 2010 and a follow up post from 2011.

Before diving too deeply, I wanted to acknowledge some of the articles and resources that I leaned heavily on while putting this post together. These include an excellent article by University of California Davis Extension Food Toxicologist Dr. Carl Winter on pesticidefacts.org, and an article authored by multiple experts from University of Arkansas Division of Agriculture Research & Extension (Dr. Amanda McWhirt, Dr. Jackie Lee, and Ples Spradley). Since both of these articles are over 5 years old, I have updated some of the information in my post to reflect any changes in the science and methodology since the time their articles were published. I also want to acknowledge that much of the regulatory information that I will be sharing within this post will pertain to agriculture in the United States, and for more detailed information on this topic pertaining to other countries, I strongly encourage you to seek out evidence-based resources and/or reach out to knowledgeable experts.

What is the ‘Dirty Dozen’

Aside from being a great World War II film from the late 1960’s, the term ‘Dirty Dozen’ also refers to a consumer-focused publication put together by an environmental advocacy group based in the United States. The Dirty Dozen is a list of 12 produce items (fruits and veggies) that allegedly contain the highest pesticide residue levels (dubbing them to be the ‘dirtiest’). This list is developed annually by the Environmental Working Group (EWG) with rankings that are based on United States Department of Agriculture’s (USDA) Pesticide Data Program (PDP) report. Although this sounds important and valuable to share with consumers, the information contained in these lists is derived through problematic methodology, disseminated using a lack of complete and evidence-based data, and results in unnecessary fear and uncertainty surrounding the consumption of fruits and vegetables that can have significant negative ramifications for growers and consumers alike.

The EWG’s “Shopper’s Guide to Pesticides in Produce” deters people from buying conventionally grown produce on the “Dirty Dozen” list, encouraging them to only purchase organic versions of these items. This annual guide also contains a “Clean Fifteen” list which includes produce items with the “lowest amounts of pesticide residues”. Neither list goes into detail regarding what these residues actually are, and whether they are even harmful to the consumer, and are therefore continually challenged by many scientists as lacking in scientific credibility.

The 2025 Dirty Dozen list is as follows:

Spinach
Strawberries
Kale, Collard, and Mustard Greens
Grapes
Peaches
Cherries
Nectarines
Pears
Apples
Blackberries
Blueberries
Potatoes

Recently harvested strawberries. Photo: **Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org**

EWG’s Dirty Dozen and Clean Fifteen methodology

Prior to 2025 EWG’s Dirty Dozen list was formulated primarily using percentages of samples with detectible pesticides and the number and amount of pesticides detected (with absolutely no information regarding the relative toxicity of these pesticides). As of this year, they have included the metric “overall toxicity of pesticides on a crop” as part of their screening criteria. Although this is a step in the right direction, it is still arguably incomplete information to share with consumers (especially since the most important component, whether these residue amounts are actually harmful to consumers, is still not addressed by any of their metrics, nor clearly communicated in their publications and marketing). This glaring omission is a big red flag in the credibility of this publication, and one of the main reasons why I have such a problem with it. As many of you avid Garden Professors Blog readers know from the many great science-based posts that have been shared (including Linda’s article on Recognizing Bad Science), we need to look carefully at the information being shared, regardless of the source, and make sure that it is evidence-based, credible, and complete.

Understanding Pesticide Safety

I want to caveat this section by stating that this is covering the science pertaining to pesticides and human health based on the research we have on this topic to date (which is subject to change as more evidence-based information comes to light). The scope of this Blog post does not cover environmental/ecological/economic/etc. impacts of pesticides in general nor the overarching impacts of various types of agriculture and food production systems (both of these are very complex topics which will require much more time and research to cover).

Although the term ‘pesticide’ is synonymously used with insecticides by many, pesticides are actually a broad category that includes all substances used to control or eliminate pests (including weeds, arthropods, vertebrate pests, pathogens, etc.). Therefore herbicides, insecticides, miticides, rodenticides, fungicides, bactericides, etc. all fall within the category of ‘pesticides’. Humans have been using ‘pesticides’ for thousands of years, though much of the innovation in pesticides (especially synthetic formulations) has occurred over the past 100 years. We have also greatly expanded our understanding and implementation of safety protocols and consideration for human and environmental health especially over the past 50 years (since Rachel Carson’s ‘Silent Spring’ and the formation of the U.S. Environmental Protection Agency (EPA) in 1970). Thankfully we have come a long way from the ‘DDT is good for ME-E-E’ era (and still have quite a long way to go). Although we are not perfect, pesticides in general are continuing to become safer and more effective, and products with higher toxicity and non-target effects are continually being phased out in support of better chemistries with fewer human health and environmental impacts (though the latter has much more knowledge gaps than the former, and we still have a LOT more work to do on this front). As we learn more about these products with scientific studies, we continue to update our protocols pertaining to them, though there are still knowledge gaps which continue to be explored by researchers. As Extension and IPM (Integrated Pest Management) professionals, we continue to educate people on the importance of pesticide safety, and urge people to think of the environmental impacts of these products, using them only after other IPM strategies (such as cultural, mechanical, and biological controls) have been unsuccessful. Anyone who uses pesticide products (whether Restricted Use Pesticides applied by Certified Pesticide Applicators and those under their direct supervision, or readily available general use pesticides such as Neem Oil, Insecticidal Soaps, etc.) should do so responsibly and in accordance with the label (the label is the LAW!), only when needed, and minimize negative environmental impacts when possible. The history of pesticides and formation of current regulatory protocols is a fascinating topic that I encourage all of you to read up on if you are interested (and may be an interesting topic for a Blog post in the future).

Home garden pesticides on a retail shelf from 1997. Photo: **Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org**

Now that we have covered pesticide basics, let’s get into pesticides and food safety in Organic and Conventional agriculture. First and foremost, if you are purchasing organic produce, that does not mean it is pesticide-free. In the United States, Certified Organic produce refers to food items that are grown utilizing a specific set of principles governed by the National Organic Program. Furthermore, there could be several conventional operations that still follow some of these principles, though may not be Certified Organic. An organic pesticide is basically a pesticide that is approved by the USDA for use in organic agriculture. Although pesticides used in organic agriculture are usually naturally derived, there are also synthetic pesticides that meet the criteria and are allowed in organic agriculture (just as there may be organic pesticides used in conventional agriculture). All pesticides utilized in the U.S. (with the exception of minimum risk pesticides) are registered with and regulated by the EPA. Any of the aforementioned pesticides that are used and sold within the U.S. have rigorous testing surrounding their safety for humans (and maximum allowable concentrations which are set at levels significantly below [10-1000 times lower] those that caused no adverse effects during testing), labeled according to these appropriate evidence-based safety guidelines, and off-label use is prohibited, routinely investigated, and enforced. Regardless of organic/conventional designation: just because something is naturally derived does not mean that it is safer than synthetically derived products. There are many natural substances that are extremely toxic (eg. Botulinum toxin, Ricin, Cyanide, Arsenic, Asbestos, etc.) and many synthetic ones that are relatively benign in comparison. In summary: Organic does not mean pesticide free, and natural/naturally derived does not mean safe.

For any of us that have taken a toxicology class, one of the most memorable take home messages was “The dose makes the poison”. Credited to a Swiss physician named Paracelsus in 1538, this statement applies to any chemicals (including water, salt, oxygen, caffeine, Aspirin, etc.) that are consumed or absorbed by us, forming the foundation of health and safety guidelines that determine the maximum allowable concentrations (tolerance levels) of these substances in our food, water, and the environment.

One of the most useful and illuminating courses I have ever taken in my career was Environmental Risk Assessment, which covered important topics including toxicology, pesticide risks, and invasive species (among other concepts). This course also detailed how Risk Assessments are conducted, the rigorous regulatory processes and evaluations required before products are even available for use, and the evidence-based tools used to determine whether a substance is hazardous and at what level (dose). A great summary of the Risk Analyses pertaining to pesticides and food safety have been summarized by Alejandro Fernández, Agronomist and Director of Hygiene and Safety of Products of Plant Origin SENASA (Argentine Food Safety and Quality Service), on the Pesticide Facts website (link in resources). These Risk Assessments and Analyses are the foundation of how we go about making determinations regarding any substances that we may be exposed to (including food and medicine).

The Issues with the ‘Dirty Dozen’

One of the biggest issues with the Dirty Dozen list is the fact that they do not communicate what having the highest (and lowest) pesticide residue levels even means. They do not conduct an accurate Risk Assessment to be able to support their message for avoiding conventional produce on this list. Although they do talk about the hazards (substances that have a potential to cause harm to us), they omit the crucial component of actual risk (likelihood of that substance causing harm to us), which incorporates another critical component of Risk Assessments: Exposure (how much of the hazard we are exposed to over a given period of time). If we looked at actual risk from the residues (incorporating hazard and exposure) we would find that the residues found on these produce items on the Dirty Dozen list are extremely low, and far below the threshold of having any risk associated with them, especially if we account for exposure (how many we consume on a daily basis, and over an extended period of time). A peer-reviewed Risk Assessment on pesticide residues published in the Journal of Toxicology by Winter and Katz (2011) in response to EWG’s 2010 Dirty Dozen list found just that (link in resources). Their conclusions were: (1) exposures to commonly detected pesticides in the 12 Dirty Dozen commodities had negligible risks for consumers, (2) substituting organic commodities for these conventionally grown ones did not result in any significant reduction of risk, (3) the EWG methodology for determining risk of these 12 products lacks scientific credibility (Winter and Katz, 2011).

Based on this cool pesticide residue calculator (link in resources), a woman of average height and weight could consume 774 servings of spinach or 453 servings of strawberries (the #1 and #2 produce items on the Dirty Dozen list) in a day without any effects. This calculator utilizes the highest possible amount of pesticide residue recorded by the USDA in these produce items, and not the average amount. Now I don’t know about you, but I would personally struggle to consume even 10 cups of strawberries in a day (every day), let alone over 450 cups. This is a great illustration of how dose/risk works, and why these produce items are considered safe for human consumption in conventional agriculture.

Pesticide residue calculator results. https://www.safefruitsandveggies.com/pesticide-residue-calculator/

In summary: the EWG fails to mention that these residue levels are still safe, and far below the thresholds that can begin to have an impact on the consumer. This can have negative ramifications for farmers that grow the produce on these lists, especially if they grow conventionally as opposed to organically. Concerns that people may opt to avoid conventionally grown produce, or avoid those specific produce items altogether is an added hurdle for growers to worry about. Both conventional and organic farmers care about what they produce, and also want our food to be safe (for their families and ours). Our regulatory processes further monitor this safety in both conventional and organic production systems, and as the science is updated, so are these processes. Although many lack access to this, if you have access: reach out to local growers and get to know what their practices are to get a better understanding, and support local farmers when possible.

Furthermore, marketing and messaging like EWG’s Dirty Dozen list discourages people from consuming certain produce, and with only 1 in 10 Americans eating enough fruits and vegetables in their diet, the cons far outweigh the pros for this messaging. An article from the Alliance of Food and Farming details some of these negative impacts (see Resources). This type of fear-mongering disproportionately impacts consumers in lower income brackets, and those that lack access to certain produce. A 2016 consumer survey showed 15% of lower income shoppers surveyed would opt to eat less fruits and vegetables after hearing about the ‘Dirty Dozen’ (Huang et al., 2016).

The take home message should be: the produce that you purchase, whether conventional or organic, is safe to be consumed (and backed by rigorous testing that determines this). Do not be deterred from eating the produce of your choice. Choose produce that is enjoyable, affordable, and accessible to you. And whether conventional, organic, or home-grown: eat more fruits and veggies!

Delicious strawberries. Photo: **Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org**

Resources:

Pesticide Facts: ‘Dirty Dozen’ List Contaminated with Non-Science:
https://pesticidefacts.org/perspectives/dirty-dozen-list-contaminated-with-non-science/

What is the “Dirty Dozen” list and should you be worried about it:
https://www.uaex.uada.edu/farm-ranch/crops-commercial-horticulture/horticulture/ar-fruit-veg-nut-update-blog/posts/dirtydozen.aspx

Organic vs. Conventional Pesticides:
https://www.pubs.ext.vt.edu/ENTO/ENTO-384/ENTO-384.html

Pesticide Facts: Pesticide Risk Analysis Ensures Food Safety:
https://pesticidefacts.org/perspectives/risk-analysis-ensures-food-safety/

USDA PDP Report (2024):
https://www.ams.usda.gov/sites/default/files/media/PDPLABOPSOP.pdf

Pesticide Residue Calculator:
https://www.safefruitsandveggies.com/pesticide-residue-calculator/

Alliance for Food and Farming: Consumer Impacts
https://foodandfarming.info/alliance-for-food-and-farming-dirty-dozen-list-scientifically-unsupportable-hurts-consumers/

Washing fresh fruits and vegetables safely:
https://extension.umn.edu/preserving-and-preparing/wash-fresh-fruits-and-vegetables

Carl K. Winter and Josh M. Katz, 2011. Dietary exposure to pesticide residues from commodities alleged to contain the highest contamination levels. Journal of Toxicology, Article ID 589674, doi:10.1155/2011/589674.
https://pmc.ncbi.nlm.nih.gov/articles/PMC3135239/

Yancui Huang, Indika Edirisinghe, and Britt M. Burton-Freeman, 2016. Low-income shoppers and fruit and vegetables: What do they think? Nutrition Today 51(5): 242-250.
https://journals.lww.com/nutritiontodayonline/fulltext/2016/09000/low_income_shoppers_and_fruit_and_vegetables__what.6.aspx

Hort couture or hubris? The growing trend of genetically engineered novelty plants

A few months ago I wrote about the newly released Purple Tomato, one of the first direct-to-consumer genetically engineered plants made available to the general public. (I’m happy to report that my Purple Tomato seedlings are growing along quite well.) Shortly after I wrote that article, I learned about another new genetically engineered plant being released to home gardeners, this time a bioluminescent petunia. So, of course you know I just had to have some.

The Firefly Petunia was released recently from Light Bio, a company based in Idaho. The company states that they grew out 50,000 plants for initial sale, but have worked with third-party growers to grow out additional plants from cuttings due to high demand for the plants.

The petunia itself is pretty nondescript. It is a small-flowered, white variety that wouldn’t get a second glance at a garden center. But the company introduced a set of genes from a bioluminescent mushroom called Neonothopanus nambi that make the faster growing parts of the plants (mainly flowers, but also other growing points) glow. The glowing is caused by a reaction between enzymes and a class of chemicals called, funnily enough, luciferins. And this is bioluminescence – it glows all the time in the dark. It isn’t like a “glow in the dark” where they have to charge up with a light source and only glow for so long.

How a mushroom gets its glow — *Neonothopanus nambi* daytime look to night time look Source: Science News

Just like the petunia, the fungus is pretty nondescript during the daytime, but glows brightly once darkness descends. I’ve seen glowing fungus once in my life. As a kid I once saw what is called Foxfire, a glowing fungus on some decaying logs. It is pretty cool seeing something glowing so eerily in nature. Now, I have that same glow in my garden.

Back to the plants. The plants are a bit of investment, ringing in at $29 per plant plus shipping, but there are some price breaks at higher quantities if you order several or put together a group order. As a startup, I suppose the company is banking on the novelty of the plant to demand such a high price to cover costs. According to several sources, these white petunias are just the start. They’re working on roses, houseplants and more.

But why glowing petunias?

Before I placed my order, I had to take a step back and think about why. Why a glowing petunia? With the tomato there is at least the case of increased health properties with added anthocyanins. But what is a value of a glowing petunia other than a novelty? Is there a purpose? Or is it just hubris? And why are there genetically engineered plants on the market all of a sudden?

While the petunias don’t have a culinary or health value, the value that they bring is one of acceptance and familiarity. For decades now, well organized and funded campaigns have spread fear of genetic engineering. Seed companies embraced “Non-GMO” as a marketing scare tactic to drive up sales due to a fake boogie man. And even bottled water and salt are labeled as “Non-GMO”. But it seems that the tide of public opinion seems like it might be turning.

Seeing the excitement around both the Purple Tomato and this bioluminescent petunia seems to show a growing interest, or at least a waning of distrust, in genetically engineered plants. And It think that is one of the benefits, or maybe the causes, of seeing genetically engineered plants on the market. Researchers have found that the online conversation about genetically engineered organisms seems to be shifting – from less polarized to increasingly favorable.

While there are sill some hiccups and some ethical and environmental issues, most scientists see genetic engineering as the most important tool in addressing issues such as endemic plant diseases affecting staple crops and developing plants that can withstand warmer and drier conditions as the climate changes. In order for us to be able to fully use these tools, the conversation needs to continue to shift to a more favorable position.

Starting off with tomatoes, petunias, and other flowers is also a choice of ease. Growing plants that don’t have native counterparts where there could be unintentional spread of genes in the wild reduces some of the regulatory hurdles plants face in the United States. And while the purple genes introduced into tomatoes could spread to plants in the food supply, the safety risk is minimal. It would be much harder to get approval for, say, a genetically engineered sunflower or coneflower where there are wild-growing natives into which the glowing genes could inadvertently spread.

Why are genetically engineered plants popping up all of a sudden?

Probably one of the reasons we are seeing so many new genetic engineering projects now is that it is so much easier. With the discovery of CRISPR-Cas9 technology, it is much easier for scientists to transform plants with DNA insertions or extractions. This technology has revolutionized the world of genetics and genetic engineering not only in the plant world, but also in the areas of human health and more.

Before CRISPR, there were a few methods of introducing DNA into organisms. The most common one for plants was probably using a plasmid from the bacterium Agrobacterium tumefasciens. This is the cause of crown gall and it works by inserting its own ring of DNA, called a plasmid, into the DNA of the plant. The plant then produces proteins based on the virulent DNA and also replicates the DNA. One of the common method was bombardment, putting the DNA on tiny microscopic beads, usually gold, and shooting them into the tissue. Tobacco mosaic virus was also used for plant genetic transformations, especially in related plants such as tobacco, tomato, and…..petunia. Most of the work I did in undergrad was with the commonly used with model plant Arabidopsis thaliana (mouse-ear cress).

The transformation, or success, rates for these methods was relatively low compared to CRISPR. Plus, where the DNA ended up was random. There was no control over where the new snippets of DNA ended up, or what genes they would disrupt, or knock-out, in the process. I did quite a bit of research as an undergrad on figuring out just what genes were knocked out in certain transformations and what that changed in their physiology or response to stimuli (our research focus was gravitropism and response to red light).

CRISPR has taken away the guessing game from genetic transformations. Scientists can now target exactly where they want genes to be inserted, or in some cases “knocked out” or interrupted so they are not expressed. For example, Arctic Apples were developed by knocking out the gene in apples that makes polyphenol oxidase, the enzyme that causes them to turn brown after cutting. This has created a technology that has the potential to substantially reduce food waste in crops that have similar reactions as well, such as potato.

So I think the trend of genetically engineered plants for consumers will continue to grow. Evolving from novelty plants to plants that serve a higher purposes, such as nutritional value enhancements, climate change resistance, and more. It will take us a while to get there, but as the technology advances so does, it seems, public opinion. Until then, I’ll just enjoy my glowing petunias and purple tomatoes.

Additional Sources

https://www.scientificamerican.com/article/this-genetically-engineered-petunia-glows-in-the-dark-and-could-be-yours-for-29/

https://www.science.org/content/article/mushrooms-give-plants-green-light-glow

https://www.fastcompany.com/91073850/glow-in-the-dark-petunias-are-just-the-beginning

Plant lists that shouldn’t exist

Nothing drives me crazier than simplistic solutions to complex problems. Given our changing climate, there has been an explosion of “drought tolerant” and “firewise” plant lists in the gardening world. Most of these lists are devoid of science and all of them are removed from reality. The fact is that taxonomy plays a minimal role in determining whether a plant will tolerate environmental extremes.

**Lack of irrigation and mulch guarantees a drought-stressed landscape regardless of the selected species.**

Let’s start with the most obvious problems with these lists. The goal isn’t to have plants that require less additional water – it’s to have a landscape that requires less additional water. Similarly, the relative flammability of plants is less important than whether the landscape surrounding those plants is protected from fire. Plants don’t exist in vacuum and unless you are strictly a container gardener a single plant’s impact on water use or fire resilience is negligible. So a gardener’s questions should be “How can I make my landscape more drought tolerant? How can I reduce the likelihood of wildfire damage?” And these are questions that can be addressed with knowledge gleaned from applied plant and soil sciences.

Drought Tolerance

***Arborvitae can tolerate droughty summers, but they don’t tolerate improper planting and management.***

First of all, let’s think about what “drought” really means: it’s an unusual lack of rainfall. It doesn’t mean no irrigation, and it doesn’t mean dry soil. Drought is a climatological term, not one associated with soil water management. Fine roots and their root hairs require water to function. Without sufficient soil water plants will go dormant or die, particularly during establishment. Plants that are drought tolerant can tolerate seasonal lack of rainfall, but they can’t tolerate chronically dry soil conditions.

***Even “drought tolerant” species like Sempervivum will die if there’s not enough soil water.***

So we need to look at the landscape factors that allow plants to survive droughts. This includes

Root systems that are well established. This means no barriers between the roots and the landscape soil system. Barriers include soil amendments and any materials left on roots during transplant (like soilless media, clay, and burlap). Obviously proper planting is key.
Adequate water movement into and within the soil environment. Anything within the soil environment that creates a textural barrier, like soil amendments, prevents water movement. Anything on top of the soil environment that creates a physical barrier, like sheet mulches or compacted layers, prevents water movement into the soil. Sheet mulches include plastics, fabrics, cardboard, and newspaper.
Adequate irrigation to support all plants in the landscape. The easiest way to determine whether there is enough soil water is to focus on one or two well-established indicator plants that you notice are the first to show wilt in the summer. That’s when the irrigation should be turned on. For our landscape in Seattle, it was a south-facing hydrangea.
Properly mulched soil. Mulch is crucial for soil and plant health, especially in terms of soil water retention and temperature moderation. The best choice for a tree- and shrub-dominated landscape is arborist wood chips. The best choice for arid landscapes is stone mulch – but if this landscape is dominated by trees and shrubs, you need the wood chip mulch. Trees and shrubs, by and large, are not the dominant plant form in arid environments. If you are going to grow plants out of place, you need to include the mulch that matches.

**The broad, thin leaves of hydrangeas lose water rapidly and make a good indicator plant for water stress.**

These four environmental conditions are key to maintaining a drought-resistant landscape. In terms of appropriate plants, just realize that plants with small, thick leaves lose less water than those with broad, thin leaves. If you want a landscape that conserves water, by all means choose plants whose evaporative water loss is the least.

Firewise Landscapes

***Jack pine (Pinus banksiana) produces cones that require fire to open and release their seeds.***

I’m not crazy about the term “firewise” as it’s not really a science-based concept. There are natural landscapes that routinely experience fires, and plants native to these landscapes have evolved mechanisms to survive moderate fires. Trees with thick bark, for example, can survive fires that are low to the ground and quick to move through. Other plants may perish in a fire, but leave behind fire-resistant seeds that are able to germinate after the next rainfall. This is not what’s meant by a firewise landscape. Instead, the premise appears to be selecting plants that are low flammability. (Jim Downer tackled this one a few years back but the message just isn’t sinking in.)

***Failing trees of any species are more flammable than living trees of any species.***

Once again, the focus of this approach is mistakenly directed to plant selection rather than landscape resilience. The best way to reduce the risk of fire is to have a landscape filled with healthy, hydrated plants and a soil protected by the least flammable mulch. The two mulches recommended for drought tolerant landscapes also happen to be the least flammable: stones and arborist wood chips.

Bark mulch is hydrophobic and flammable in the landscape.

Despite published evidence that arborist wood chips are not very flammable when compared to all other organic mulches, many governmental groups specifically recommend against them. This is a problem. Stone mulches are great choices IF the plants in question are native to arid zones. Trees and shrubs that are not from arid zones generally require the presence of woody debris to enhance mycorrhizal and root health. Without the proper mulch, these woody plants are less healthy and likely less hydrated than their counterparts under arborist chip mulches. That makes them more, not less, susceptible to fire damage.

***A stone mulch in a southwestern desert landscape.***

Most of the confusion around arborist chip mulches is probably the result of regulatory agencies confusing bark mulches with wood chip mulches. Bark mulches ARE flammable as they contain waxes and are not great choices for root and soil health. They should be avoided. Agencies associated with fire control methods need to be better informed about the significant differences between these two types of mulches and how they affect plant resilience.

***The wildland-urban interface faces the risk of extreme fire danger. [Photo byAnthony Citrano]***

And finally, it is important to understand that major wildfires are going to burn anything that’s organic. If you live in such an environment, the best thing you can have in your landscape is no plant material of any sort. A buffer of stone mulch is the only logical option.

Everything is chemicals: the myth and fear of “chemical-free” gardening

“Chemical-free” – a term I’ve seen several times attributed to many products, especially food and produce at farmers markets and even in gardening circles these days. This term is often misused to describe plants grown without the use of any pesticide, either conventional or organic. I have my thoughts that I’ll share later on that subject but first let’s talk about this “chemical-free” that gardeners, farmers, and others use and why its not only a myth, but a dangerous one at that.

Ain’t such a thing as “chemical-free” anything

At face value, the term “chemical-free” would literally mean that whatever the label is applied to contains no chemicals. That the entire item, whether it be animal, vegetable, or mineral is devoid of any and all chemicals. Factually this can never, ever be true. Everything that exists is made of chemicals. Oxygen, water, carbon dioxide, and any simple molecule, by definition, is a chemical. Plants and animals are organized structures filled with complex chemicals. Even you and I, as humans, are walking, talking bags of chemicals. The air we breathe, the food we eat, and the water we drink are all composed of a great mixture of chemicals. The use of the term “chemical-free” to describe anything is uninformed at best, and intellectually dishonest at worst. But a bigger problem, as we’ll discuss later, is that using the term can cause confusion and even fear of things as simple as food and as complex as science and medicine.

Expert reveals how even natural foods contain chemicals | Daily Mail Online — The “ingredient list” of a peach.
Source

What most people intend to say when they use the term “chemical-free” in relation to plants or produce is that they are produced without use of pesticides or conventional “chemical” fertilizers. Therefore, a better term to use would be “pesticide-free” instead of “chemical-free” as it more accurately represents the situation. Many may ask why the term “organic” or “organically grown” couldn’t also be used to describe “pesticide-free” plants. And while those terms would be accurate, organic production can involve the use of organic pesticides that are derived from natural sources such as plants, bacteria, or natural minerals. Natural sources of fertility for plants, such as composts and even soil itself, are all composed of a myriad of chemical substances. Plants don’t differentiate between the chemicals they uptake from compost or soil and those from fertilizers. To plants, nitrogen is nitrogen and phosphorous is phosphorous no matter where it comes from.

For some clarification on what different growing and production terms like these mean, check out this lecture I gave for the Oregon Farmers Market Association earlier this year.

While many have a strong opinion on the use of pesticides and fertilizers, I’ll state here that the use of any pesticide, organic or conventional, must follow the label on the container by law. And the use of any pesticide according to the label instructions means that the use of that pesticide should present a minimal risk to the health of the applicator, consumer, off-target species, and the environment. And don’t use any home remedy recipes or products that aren’t labeled (or at least scientifically researched) for use as a pesticide. In most cases these remedies aren’t effective, in some cases they can be more dangerous to human health or the environment than the pesticide they are trying to replace. And applying them as a pesticide could also be illegal.

Reading Pesticide Labels - Pests in the Urban Landscape - ANR Blogs — Pesticide label signal words that denote relative toxicity of a given pesticide.

Any gardener or producer, whether they use pesticides or not, should also be practicing Integrated Pest Management (IPM) to decrease or mitigate the effects of insect and disease pests on their plants. For those using pesticides, use of the least toxic pesticide that offers control of the problem should be the last step in a series of steps to avoid damage from pests after a threshold of damage has been reached. For those who don’t use pesticides, IPM should be a central practice in their gardening or farming practice. Unfortunately, the tradeoff for not using pesticides is often time and labor, so successful “pesticide-free” growing often involves more work (and for produce at the market or grocery store, a higher price). I have seen some gardeners and farmers who don’t use pesticides and don’t make an effort to practice IPM, taking whatever plants or produce mother nature and her children deal them. I’ve sometimes referred to this type of growing as “organic by neglect” as I see insect and disease riddled produce harvested and even sold at local farmers markets.

Why does it matter?

“So what if I use the term ‘chemical-free’? It doesn’t hurt anyone,” you may say. While this may seem the case, the use of the term “chemical-free” has risen as a result of what many call chemophobia, effects that reach far beyond the garden or the farmers market. This kind of thinking leads to the incorrect notion that all “natural” remedies are safe and all “synthetic” remedies are dangerous. True, many chemicals do pose a risk to human, plant, animal, and environmental health but many do not. Just like not all natural substances are safe. Poison ivy, anthrax, botulinum, and cyanide are all natural and cause everything from a skin rash to instant death (sometimes I get poison ivy so bad I wish for instant death).

This chemophobia can lead to, or is a symptom of, a broader mistrust of science, the scientific process, and modern medicine that has developed in society in the last few decades. Many attribute this to an anti-intellectual or anti-science stance in society resulting from mistrust or political saber-rattling against universities, education in general, science/scientists, “big Pharma”, “big Agriculture”, and others. As a result, the news is filled with people who eschew well-researched scientific advances that have been proven safe and instead turn to home remedies that have no such guarantee of either effectiveness or safety. The results can be worse than the effects of the proven advance the person was trying to avoid.

While the outcomes of “chemical free” gardening might not have such dire consequences as immediate death, the misuse of such terms can feed into a cycle of anti-science cause and effect, serving as both a cause and a symptom of mistrust of science and the scientific process. While everyone has a right to choose whether or not they use pesticides (or any other scientific advancement), making such decisions from a place of knowledge instead of fear is paramount for success and continued advancement.

Sources and further reading:

https://www.columbiasciencereview.com/blog/debunking-the-myth-of-100-chemical-free-slogans

https://www.sciencedirect.com/science/article/pii/S0278691520302787

https://www.canr.msu.edu/news/chemophobia-fearing-chemicals

https://www.businessinsider.com/what-chemicals-are-in-an-all-natural-banana-2017-6

Garden Logic – understanding correlation and causation in our gardens and landscapes

*This home landscape is managed using science-based methods; the only routine additions are water and arborist chip mulches.*

Upon reading this post’s title, you may be inclined to stop right there. (That’s why I have an eye-catching photo to lure you in.) While logic may seem irrelevant to your enjoyment of gardening, I can guarantee that reading this blog post will challenge many seemingly logical assumptions you’ve heard or read about. Recognizing unsubstantiated assumptions and avoiding their pitfalls means you can make wise choices about how you care for your gardens and landscapes.

*You can find this and thousands of other silly correlations at www.tylervigen.com*

A few definitions are needed before we get started:

Correlation refers to variables whose changes mirror one another. For instance, the addition of nitrogen fertilizer to container plants is correlated to plant growth: as nitrogen levels increase so does plant growth. You can also have inverse correlation, where the variables move in opposite directions. An example is water availability in soil and planting density: the more plants you have in a specified area, the less water is in the soil.

*Plant growth is correlated with increased nitrogen and other nutrients (from Xu et al. 2020)*

Causation takes correlation one step further: it establishes that one of those variables is causing the change in the other. Using the same examples, we know through published evidence that the increase in nitrogen is causing the increase in plant growth, and the increase in planting density is causing the decrease in soil water because of competing roots. These relationships are obvious to us, but what’s important is that these causative effects have been established through scientific experiments.

*Inverse relationship between planting density and soil water content (from Shao et al. 2018)*

Sometimes scientific evidence doesn’t exist to demonstrate causation. That may be because it’s impractical or impossible to run an experiment that tests for a causative effect, or it may be because the experiments just haven’t been conducted yet. The latter is the unfortunate reality for those of us interested in managing gardens and landscapes: there is no major funding agency that supports field research for us. There is research being done, but it’s on a small scale with a shoestring budget…so the body of literature develops very slowly. In such situations, we must rely on established applied plant physiology and soil science to ask whether a suggested correlation might be elevated to causation.

*Something caused these arborvitae to fail…but what? Research is slow to catch up to our observations of landscape failures.*

Which brings me to my current source of online irritation: the constant blaming of tree failure on mulch volcanoes. Yes, tree failure is definitely correlated with mulch volcanoes – because lots and lots of newly planted trees fail. But is the mulch to blame? No one seems to care much that there is NO published work to show that mounds of appropriate mulch materials will somehow kill otherwise healthy trees. Instead, observers jump to the conclusion that thick layers of wood chip mulch kill trees. They are elevating correlation to causation in the absence of either experimental research OR known plant physiology. In fact, there is published research to show that thick layers of arborist wood chip mulch enhance tree establishment and survival. And there are many poor planting practices that increase the likelihood of tree failure. But it’s easiest to blame the wood chip mulch, though it’s merely masking a multitude of planting sins.

Not interested in mulch volcanoes? Well, there are lots of other examples of garden and landscape management practices or phenomena that fall into the logical fallacy camp. I’ve linked to appropriate references, when available, that go into more detail:

Black walnut allelopathy;
Companion planting;
Hot-weather watering and leaf scorch;
Hugelkultur;
Humus formation and importance in soils;
Lasagna mulching;
Native plant superiority;
and just about any gardening product you can think of where there is NO published evidence – or appropriate, established plant or soil science – that supports any causative, beneficial effect on plants or soils. Cornmeal, Epsom salt, gypsum, and kelp products are just some of these.

All of these products, practices or phenomena are correlated with some anecdotal observation (increased yield, healthier soil, plant failure, etc.) that elevates them to causative relationships. But no science.

I’d encourage you to think objectively about your closely held beliefs about your gardens or landscapes. Are you sure that what you’re doing is actually beneficial? How do you know there’s a cause-and-effect relationship? I’m not going to talk you out of your cherished beliefs – but if you are a science-based gardener, you might talk yourself out of them instead.

Willow screams in pain
What is its source of anguish?
More research needed!

SUPER Thriving Lettuce?

The Garden Professors have previously written about the ubiquitous garden center product, SUPERthrive, here and here. The manufacturer claims a plethora of beneficial uses for SUPERthrive —everything from Christmas tree care to turf to hydroponics. They claim SUPERthrive will “revive stressed plants and produce abundant yields” and that it “encourages the natural building blocks that plants make for themselves when under the best conditions” thus “fortifying growth from the inside out,” but I know of no body of rigorous, peer-reviewed literature to support any of those claims (1, 2, 3, 4). In fact, I’m not entirely sure what those claims really mean, but I’m encouraged on their website and bottle to use it on every plant, every time I water, to receive these amazing benefits!

A test case

The hydroponics claim intrigued me because during the winter months I grow plants hydroponically under lights. One of the benefits the manufacturer claims is “restores plant vigor” and “works with all hydroponics systems.” As a plant scientist, and knowing something about the ingredients, I was skeptical to say the least, but I thought that if SUPERthrive was going to show any beneficial effect it would surely be in hydroponics since that is a more uniform environment than outdoors. So, I shelled out my $11 for 2 oz (the things we do for science!) and set off to design a simple experiment.

The hypothesis

A typical experiment like this starts with what we call the null hypothesis (denoted “H0”). The null hypothesis is defined prior to the experiment and often states that we think there will be no difference between the treatment and control. In this case, my null hypothesis is that the SUPERthrive treatment will have no effect on the mean fresh weight of the harvested lettuce relative to the control lettuce. Note that I haven’t made any hypotheses about other parameters that might be important, e.g., flavor, compactness, number of leaves, color, disease incidence, survival rate, etc. For this experiment I am interested in only one thing: total harvested weight as a signifier of healthier plants.

After the data is collected and analyzed, we decide whether to accept or reject the H0 by running an appropriate statistical test. If there is no statistically significant difference, then we cannot reject the H0—that is, we accept the H0 that there is no difference between treatment and control. If there is a statistically significant difference between treatment and control, then we say we reject the H0 and conclude that the treatment did have an effect. Keep in mind, sometimes no difference between treatment and control is a good thing, e.g., in toxicity studies.

Experimental design

With my skeptical spectacles on, I set up my experiment to test my hypothesis. I made a six-gallon batch of hydroponics nutrients suitable for leafy greens. I split the batch in half and added SUPERthrive, per the manufacturer’s dilution recommendation, to one of the three-gallon aliquots as the treatment. I then divided the control and SUPERthrive treatment each into six individual, identical, two-quart containers. I thus had six independent replicates of a treatment and a control. (See Figure 1 below for a schematic of the experimental design.)

To further avoid any experimenter bias, I had my wife assign numbers randomly to each container, record which were SUPERthrive treatment and which were untreated control, and then re-sort all the containers. I had no idea which containers contained which nutrient mix. I did not open the “secret decoder envelope” until after all measurements were complete!

Figure 2. Identical 2 quart containers randomized on day 1 in the hydroponics solutions. This kind of hydroponics is called “Kratky” or passive. Enough nutrient solution is supplied at the beginning to last the plant for its entire life-cycle.

Into each of the 12 containers I placed a 12-day-old lettuce seedling, taking care to select plants that were of equal size and leaf number. The containers were then placed under my lights (cool white T8 fluorescent) for the remainder of the experiment. I rotated the rows of plants several times to try to control for any edge effects in my grow area. After 30 days in the containers, I harvested and weighed each plant.

*Figure 3. Plants after 30 days of growth.*

What did my experiment show?

The graph below is a box and whisker plot that shows the spread of the data and the mean for each group in grams of harvested fresh weight of the plants (roots were removed). In my experiment, the SUPERthrive treatment showed a clear drop in harvested fresh weight! In fact, the heaviest SUPERthrive plant weighed less than the smallest control plant, and the SUPERthrive set was much more variable in harvested weight. These results surprised me a bit.

*Figure 4. Box and whisker plot of lettuce plant fresh weight. Master Blend: Master Blend nutrients; Master Blend + ST: Master Blend nutrients plus SUPERthrive (0.9 ml/gal.)*

A standard statistical test (Student’s T-test, unpaired, two-tailed) was performed to show that that there was in fact a statistically significant difference (p<<0.01) between the two groups. Thus, we can reject the H0 (remember our null hypothesis is that there will be no treatment effect) and conclude that there is a difference between treatment and control harvested weights, with the treatment mean plant weight being significantly smaller than the control mean plant weight.

What can we make of this experiment?

Well, we need to keep in mind a few things.

1) Six replicates is a very small sample size; this could be a spurious, unlucky result. There is always some distribution of growth rate, even in a uniform genotype. Did I get unlucky and happen to put six plants that would always be on the smaller end of that distribution into SUPERthrive?

2) After analyzing the data, I discovered that four of the SUPERthrive plants ended up in the same row and were the smallest heads in the experiment (sometimes you flip a coin and get four heads in a row!). Could this be the reason for the unexpected results? The other two treated plants were in the other two rows, but neither was as large as the smallest control plant.

3) I do not have a perfectly controlled environment like one would find in a lab or even in a larger growing facility. However, something marketed with such aggressive claims of amazing plant health benefits and vigor should give a noticeable effect under a variety of imperfect, real-world conditions, such as those one would find in a home garden situation, don’t you think?

4) Perhaps my plants were already growing at their maximum potential and there was nothing for SUPERthrive to “improve.” Afterall, hydroponics indoors is already a relatively stress-free environment, as the SUPERthrive manufacturer also points out. Then what do they think their product is improving in hydroponics? Would I have seen an effect under less-than-ideal or more stressful conditions then? This could certainly form the basis of other testable hypotheses.

Conclusions

What I think we can conclude is that in this experiment, with this genotype of lettuce, and under these hydroponics conditions and environment, SUPERthrive had no positive effect whatsoever and may have even had a negative effect. Under other conditions would one see a positive effect? Possibly. Would different plants or genotypes respond to the SUPERthrive differently? Possibly. We must always be careful of over-extrapolating both positive and negative results from a single experiment.

But, because the individual ingredients have not been shown to provide any beneficial effect, and no plausible mode of action is given by the manufacturer for their broad general claims, we should remain highly skeptical. As pointed out in the previous post, the SUPERthrive manufacturer has certainly had plenty of time to scientifically demonstrate efficacy of their product, since they proclaim to be “always ahead in science.”

Because the results showed a clear and unexpected negative effect, the experiment surely needs to be repeated. Repetition is a central tenet of science. I hope to share additional results with you in a post later this spring—after all, I have a whole bottle of SUPERthrive and we love salad!

References

Banks, Jon & Percival, Glynn. (2012) Evaluation of Biostimulants to Control Guignardia Leaf Blotch (Guignardia aesculi) of Horsechestnut and Black Spot (Diplocarpon rosae) of Roses. Arboriculture & Urban Forestry. 38(6): 258–261
Banks, Jon & Percival, Glynn. (2014) Failure of Foliar-Applied Biostimulants to Enhance Drought and Salt Tolerance in Urban Trees. Arboriculture & Urban Forestry 40(2): 78–83
Chalker-Scott, Linda. (2019) The Efficacy and Environmental Consequences of Kelp-Based Garden Products.
Yakhin Oleg I., Lubyanov Aleksandr A., Yakhin Ildus A., Brown Patrick H. (2017) Biostimulants in Plant Science: A Global Perspective. Front. Plant Sci., 7:249

Not all Extension publications are created equal

(A friendly caveat – this post does not lend itself well to images. So the pictures here are simply eye candy from my 2019 trip to London to reward you for considering this visually drab but important topic.)

The actual “whomping willow” in Kew Gardens

I’ve been involved in Extension education for 17 years and one of the most important things I’ve learned is that Extension audiences want information that’s easily understood and has obvious practical use. Most peer-reviewed research articles are written for academic audiences, so only the most persistent nonscientists will slog their way through pages of dense, technical writing. It’s up to Extension educators to accurately translate and summarize technical scientific information for use by the public.

Epiphyte “tree” in Kew Gardens glasshouse

Extension is part of the American land-grant university system and extends traditional academic teaching to citizens statewide (hence the term “extension”). In addition to providing seminars and workshops to interest groups, Extension publishes educational materials in-house and provides them at low or no cost to their clientele.

But here’s the problem: the standards for Extension publications are set by each university. Unlike the peer-review system adopted by reputable journal publishers, Extension publications can vary widely in quality. Some universities have adopted a system that parallels that of scientific journals in that they require double-blind peer review. But many universities have not – and this means that looking for Extension publications on a particular topic results in a collection of materials with contradictory messages. This is incredibly frustrating to confused nonscientists and to Extension faculty who have to sift through the mess to find publications that are relevant and science-based. As a result, Extension publications are often regarded with suspicion by both nonscientists and academic faculty (who often do not have the disciplinary expertise to sort through the mess). Since I was a traditional academic before entering Extension, I have a foot in both camps.

Nonscientists are probably not going to have the disciplinary expertise to tease out the good stuff from the dreck. But they can look for some indicators that will help them identify the most reliable publications. Here’s a checklist to start the process: the more “yes” answers you have, the better the chances are that the information is reliable.

Is the author identified? Anonymous publications are not reliable.
Is the author an expert? Expertise is determined by advanced degrees (at least a Master’s degree) in the subject matter.
Is the publication peer reviewed? There should be a logo or a statement on the publication that says so.
Is the publication relevant? High-quality Extension publications targeted towards commercial agricultural production are usually inappropriate for use in home gardens and landscapes.
Is the publication current? Information relative to urban horticulture and arboriculture is rapidly changing. Publications over 10 years old likely do not contain the newest information.
Are there scientific references included, either as citations or as additional readings?

As necessary as this process is for identifying reliable information, there can also be negative outcomes. Universities that do not have a rigorous process for publishing Extension materials put their Extension faculty into the uncomfortable position of having to defend their work when it’s questioned. It would benefit all parties for every land-grant university to institute a rigorous, peer-reviewed process for their Extension publications.

Hydroponics for the Holidays? Home Systems are a hot holiday gift list item

Systems to grow fresh produce in your home using hydroponics or other automatic processes have been popular for several years but seem to be even more popular this year with more folks home and looking for something to do and hoping to produce their own food. As a result, these systems are popping up on holiday wish lists and gift buying guides all over the internet. But are they worth it? And if so, what should you look for in a system?

First off, what are these systems? And what is hydroponics? Hydroponics is the process of growing plants without soil in a aqueous nutrient solution. Basically, you provide all the nutritional needs of the plants through nutrient fertilizers dissolved in water. These systems can grow plants faster and in a smaller space than traditional soil-based production. It also allows you to grow plants indoors and in areas where you would not normally be able to grow.

This Aerogarden (which is the previous generation) has a digital brain that controls light and water schedules for the specific growth phase of the plant and yells at you when it thinks you need to add more fertilizer solution.

As for systems, you might have seen what is probably the “oldest” one on the market – the AeroGarden. Since it is the oldest and most common, that’s the example we’ll be staying with. It has been around a few decades and has evolved from a basic electronic system to fully automatic, “smart”Bluetooth connected systems that you can control with your phone. In recent years there have been many new systems come onto the market at all different sizes and price points. A quick search of online retailers will usually provide an array of options – from DIY kits to plug-and-play enclosed systems such as “Click & Grow” and “Gardyn”. My only experience is with the Aerogarden system, so I can’t speak to any of the others (though I’d love to try them out!).

The answer to “are they worth it” is up to you, really. Most home based hydroponic or aeroponic systems offer convenience, but at a cost. Most cost several hundred dollars and are small, so they produce a small amount of produce (or other plants) at any one time. So you have to determine what goals you, or your intended giftee, have with the system.

“Baby” lettuce, 18 days after sowing. The current version of this 9-plant Aerogarden system, called the “Bounty”, retails for $300 but you can usually get it for under $200 on sale.

The benefit of the “plug-and-play” enclosed systems like the AeroGarden is that basically you can take it out of the box, set it up in less than 10 minutes, and have some fresh lettuce or herbs in a few weeks. It controls the water cycles, lighting, and all other conditions for growth. You just drop in pods that contain the seeds suspended in a spongy-material. The smallest system, that holds 3 plants, retails for $100. As an additional expense comes from buying refill kits to replant. The mid-size systems are the most common and range from $150-$300. The largest system, the “XL Farm” retails for $600. But these systems are commonly on sale at pretty significant discounts.

For many systems, you typically buy a new set of pods (there are different plant variety selections), but there are pods you can buy to assemble your own using your own seeds. For the AeroGarden, the pod kits range from $15 up to $30 to grow up to 9 individual plants. There are other plug-and-play systems on the market, as well as some kits that are more build-your-own and less automated.

No matter which systems you buy (or gift), keeping these costs in mind is important. If you’re looking for a fun and easy activity with the benefit of a little fresh produce and aren’t as concerned with production costs these systems may be for you – and if you are giving or getting them as a gift that definitely makes it more economical. But given the cost of the plug-and-play systems and the refill pods, they will never be an “economical” option for producing your own food. If you are wanting to produce food on a budget and you’re interested in home hydroponics, look for plans to build your own or buy a DIY kit.

GPs at the Tradeshow: Looking for snake oil and finding…..the dirt on tillage

The Annual Meeting and Professional Improvement Conference of the National Association of County Extension Agents is that one time of year where extension agriculture professionals gather to share ideas, give talks, network, and let their hair down. The name of the organization is a bit outmoded: many states no longer call their extension personnel agents, but rather educators, experts, professionals, area specialists, and the like. Most aspects of agriculture are included: from the traditional cows and plows of animal science and agronomy to horticulture and sustainable agriculture (I’m the outgoing national chair of that committee). There’s also sharing on agriculture issues like seminars on engaging audiences about genetic engineering, teaching and technology like utilizing social media and interactive apps, and leadership skills.

It is the one time every year or so that Linda Chalker-Scott, grand founder of the Garden Professors, and I get to hang out. If we’re lucky we’ll meet up in some sessions, chat in the hallways, or grab a drink. But one of our favorite conference activities is taking a turn around the trade show floor. This is where companies and organizations are vying for the attention of extension educators to show them their newest equipment and products….we are, after all, the people that share growing and production information with a great number of potential clients across the country.

Since the organization runs on money, almost no company that comes calling with the money for a trade show spot is turned away. This means that the products may or may not stand up to the rigors of scientific accuracy. In years past we’ve found snake oil aplenty, like magical humic acid that is supposed to be this natural elixir of life for plant growth. The only problem is that humates don’t exist in nature and there’s little documentation of any effect on plant growth. The product that was supposed to be this magic potion was created from fossil fuels and no actual peer-reviewed research was offered by the company – hardly convincing. There were magic plastic rings that supposedly acted as protective mulch around mature trees and could slowly release water, except that mature trees don’t really need protective mulch and the amount of water would be negligible to a tree that size. So will we be smiling or scowling when we’ve made our way through the trade show.

Right off we set our sites on a company starting with “Bio”, which can be a good indicator of questionable rationale. That lit up the first indicator on our woo-ometer. Beneficial bacteria you apply to plants/soil: woo-ometer level two. So LCS and I engaged the representative. Asking about the product and what it does. We learned about their different products that could help increase the rate of decomposition of crop residues in farm fields, of turfgrass improvement, increased crop production, and treatment of manure pits on dairy and hog farms (which, if you’ve ever experienced one, you’d know would benefit from any help they can get in terms of smell).

Most of the products like this give vague descriptions of the beneficial bacteria it contains. They’re akin to compost teas that can have any number of good, bad, and downright ugly bacteria and fungi in them. Since you don’t know what’s in these products, any claims on soils or plants are suspect at best. However…our rep went on to tell us that the company created blends of bacteria from specific strains that had been researched for their effects on decomposition, soil nutrient availability, and plant growth. There was a brochure with the specific bacteria listed, along with studies the company had conducted.

We asked about peer-reviewed research, which is our standard for evidence here at the GP, and while he had no results to share he assured us that university-led research is currently in the works. And as we’ve stated in regards to applying of beneficial bacteria to soil – while there’s little evidence showing the effectiveness of applying non-specific bacteria to plants, using directed applications of specific bacteria which have been tested for specific functions are supported by research. So our woo-meter didn’t fully light up. We reset it and continued the hunt.

We scoured the rest of the trade show and found one other soil additive that lit up the first lights of our woo-meter, but the rep must have been out for lunch so without anyone to talk to we couldn’t confirm woo or no-woo.

However…..we did find something spectacular! The local employees of the USDA NRCS (Natural Resources Conservation Service) had an interactive demonstration of soil, specifically showing the benefits of reducing or eliminating tillage. The NRCS works with many farmers to incorporate conservation practices on farms, including no-till production, by providing technical assistance, farm plans, and even grants, cost-share, and easement programs. Many farmers have benefitted from their grant for season extension high tunnels (which are seen as a soil conservation technique, since they shelter soil). We were so enamored with the demonstration, we asked them to do it again…so we could record it. So, for your viewing pleasure check out the video below where you can see how well no-till soil holds its structure while tilled soil falls apart. This effect is from the exudates from all the beneficial microbes in the soil that act like glue to promote good soil structure. We’ll let the video speak for itself……

So not only does the trade show get a smile instead of a scowl from us, but also two thumbs up! Either there has been some weeding out of the trade show sponsors, maybe the snake oil salesmen didn’t get the traction they were hoping for at the conference, or hopefully some of these companies have failed to reach an audience with their pseudoscience.

Is it good advice? Or is it CRAP?

In my educational seminars I’ve long shared a version of the CRAAP test (currency, relevance, authority, accuracy, and purpose) for analyzing information related to gardens and landscapes. My version is CRAP (credibility, relevance, accuracy, purpose), and we’ve published an Extension Manual that explains in detail how to apply it. This past week I was at the Philadelphia Flower Show participating in Bartlett’s Tree Care Update panel. Given that the theme of the show was “Flower Power,” I figured that a talk on Magical Mystery Cures was in order. And the 1960’s was the decade where the late Jerry Baker gained prominence as a garden authority – and whose presence is still widely felt nearly 60 years later.

And anthropomorphizing of plants begins….

Now, I could spend the rest of the year discussing all of Jerry’s advice, tips, and tonics for gardens – but it’s more useful to determine whether he is a credible source of reliable information. So let’s apply the CRAP test.

C = credibility. What are Jerry’s credentials as a garden expert? It’s easy to find this information from the internet, including the Jerry Baker website. He had no academic training in plant or soil sciences but started his career as an undercover cop who often posed as a landscaper. His books are all popular publications, meaning they have not gone through critical review by experts before publication.

R = relevance. For our purposes, his information is relevant to our focus of managing gardens and landscapes (as opposed to production agriculture, for instance).

A = accuracy. Jerry’s advice is not based on any scientific source. He relies on common-sense approaches, folklore, and his grandmother’s advice. In fact, many of his assertions are at odds with published scientific evidence. Now, science evolves, and older scientific publications are sometimes found to be inaccurate after new information comes to light. If Jerry’s books were meant to be accurate sources of information, they would be updated with new findings as subsequent editions were published. This is what happens with textbooks, for example.

P = purpose. What is Jerry’s ultimate purpose? It’s sales. There’s no way around this conclusion. Over twenty million copies of his books have been sold, and during his career he became the spokesperson for several gardening products. Probably the most well-known of these was the Garden Weasel (which parenthetically is a great way to destroy fine roots and soil structure). There’s no doubt he was a brilliant self-promoter and marketer. But he was not a reliable resource, and many of his “tips and tonics” are extraordinarily harmful to plants, pets, and the environment.

While I was wrapping up my research on Jerry Baker I was particularly taken by a chapter in one of his books (one of his Back to Nature Almanacs) called “The Tree Quacks.” I thought some of these quotes were particularly ironic:

Imagine my surprise when I discovered that these quotes were actually not his own. In fact, the entire chapter was plagiarized from a 1964 article by John Haller in Popular Science, which is online. This action is uncomfortably similar to his 1985 trademarking of the phrase “America’s Master Gardener,” 12 years after the Master Gardener program was formed (but not trademarked) at Washington State University.

I hope this post has helped you learn to analyze the credibility of information and information sources. If so, you can claim the of America’s Master CRAPper ™!