Written by: Di Graski

1. Why & Survey Responses.

Green School taught us to sanitize our garden tools because our tools can be a vector for transmitting biohazards from an infected plant to healthy plants: insect eggs, harmful bacteria, viruses, fungus and mold spores. So, what do our fellow Pueblo County Master Gardeners say about their tool-sanitation routines? A very unscientific survey was conducted in August 2024, and I am truly grateful for the high rate of responses to my inquiries – thank you!

Fourteen Pueblo CMGs and myself, we are all over the map! Five of us (myself included) don’t do anything to sanitize our garden tools, and we know we need to change our evil ways. I am embarrassed that Green School provided me with the knowledge to do better, and yet I have failed to follow through and actually change my behavior. Why, oh why?

My theory is that sanitizing garden tools has to be a part of my toolkit: the necessary materials should be so utterly accessible, conveniently located, handy, and efficient that any excuse I might have had fades away. The risks we run when we fail to sanitize our garden tools are microscopic organisms, not “in your face” enemies like Japanese beetles and grasshoppers. And the ill effects are probably off in the future – when the eggs hatch next spring or the microorganisms start dividing – so the reward of doing the right thing is not immediate. Changing my behavior means I have to remove all obstacles, because the risk/reward feels a bit hypothetical.

Happily, ten of our fellow Pueblo CMGs have great suggestions for making it easy to do the right thing. Five use good, old sodium hypochlorite – bleach –diluted either in a spray bottle or a sink. Three use isopropyl alcohol, rubbing alcohol, usually poured onto a paper towel or rag. Three use vinegar. And three use disinfectant wipes, those super-convenient towelettes you pull one-at-a-time out of a dispenser.

2. Pros and Cons of Sanitizing Candidates.

I was surprised by the diversity of sanitizing solutions, and it got me wondering: are they all equally effective? Maybe some are better on some microorganisms but not others? What are the pros and cons of each of these sanitation products? We have COVID to thank for a lot of current research on disinfectants, and the purpose of this article is to share those findings with you.

There are at least two common challenges across all the disinfectants Pueblo CMGs use on their garden tools. The first is that their effectiveness diminishes when they are applied to a dirty target: any soil, sap, or plant material on a garden tool will interfere dramatically with these disinfectants’ power to reach and destroy microorganisms. A 2010 article from our Extension colleagues at Ohio State University reminds us of a fact that all bartenders know: effective cleaning means first washing to remove all organic matter, then sanitizing, and then rinsing, all three steps, exactly in that order.[i]

The second common challenge is that we live and garden in an arid environment, and liquid disinfectants might evaporate before they have had a chance to do their work. Our colleagues and neighbors at Northern Arizona University created a comparison chart of disinfectants that refers to this characteristic as “dwell time”: how long must a liquid disinfectant remain on a target surface to destroy microorganisms?[ii] The typical answer is ten minutes. And, of course, another oft-repeated Green School lesson is “Read The Label!”: ten minutes is what the teeny-tiny print on my wipes’ label recommends, also. Depending on our weather conditions, it is impossible for us Puebloans to keep a liquid from evaporating in less than ten minutes.

On to some of the unique pros and cons of different sanitizing solutions.

Bleach

Sodium hypochlorite is classic laundry bleach. It is cheap, sold almost everywhere, and most of us probably already have it on-hand. The good news is that bleach is also “effective in inactivating vegetative bacteria, fungi, lipid and non-lipid viruses.”[iii]

For years, my husband and I have kept a bleach-water spray bottle handy in our kitchen, a roughly ten-to-one mixture of water and bleach that is convenient to sanitize the sink after handling raw meat or to disinfect foster kittens’ cat boxes and plastic toys. Researching this article, I was shocked to learn that pre-diluted bleach is only effective for about 24 hours – evidently, the act of mixing bleach with water diminishes the sodium hypochlorite’s effectiveness pretty quickly.[iv]

Another concern with bleach is its corrosiveness, especially on metal and wood, two materials that make up a lot of our garden tools.

Disinfecting Wipes

Wipes are not bleach, despite the “Clorox” brand on some products; instead, disinfecting wipes use active ingredients affectionately known as “the Quats,” Quaternary ammonium compounds like n-Alkyl Dimethyl Benzyl Ammonium Chloride and n-Alkyl Dimethyl Ethylbenzyl Ammonium Chloride. Like bleach, these wipes are relatively inexpensive, sold almost everywhere, and are probably already available in your home.

Three advantages of wipes over bleach are their sheer convenience – just throw a tub in your garden-tool bucket – their reduced corrosiveness to metal, and their more stable shelf life. However, they are just not as effective on some microorganisms as bleach is, especially spores.[v]

Isopropyl Alcohol

Rubbing alcohol is also cheap, readily available, and most likely already in your bathroom medicine cabinet.

For alcohol, strength matters: a 50% solution is not very effective as a disinfectant; a minimum of 70% is needed to combat microorganisms.[vi] And dwell time matters: soaking garden tools in a bath of alcohol would probably be effective; wiping the surface of garden tools with alcohol probably can’t achieve the ten-minute mark.

Vinegar

Like our other candidates, distilled white vinegar is cheap, easy to find, and probably already on your shelves at home. But is it an effective disinfectant? Lots of researchers conclude “no”: the acetic acid in vinegar surely can help clean our garden tools (step 1) but “we just don’t know that it’s effective against bacteria and viruses.” (step 2).[vii] However, our colleagues at Ohio State University’s Extension suggest that heating distilled white vinegar to at least 130 degrees Fahrenheit makes it a more effective disinfectant and definitely reduces the dwell time.[viii]

3. Other Strategies?

Some of our fellow Pueblo Master Gardeners mentioned additional sanitizing products in their responses, including Lysol and Simple Green. One of my favorite suggestions is totally free and wildly abundant: the Ultraviolet rays of Sunshine! During the pandemic, I felt good about hanging clothes and linens out to dry, imagining all those COVID viruses shriveling and dying a painful death in the sun. And some research supports my daydream: “UV light has been used for decades (yes, decades!) to reduce the spread of bacteria.”[ix]

However, researchers also want us to be aware of some caveats: the most potent UV light for combatting microorganisms is UVC, but UVC is blocked by Earth’s ozone layer, so it won’t make it to your garden tools. “UVC . . . has the shortest wavelength and the highest energy of all the UV radiation, [so it] is a known disinfectant for air, water, and nonporous surfaces.”[x] And it turns out that sunshine needs the two step, too: “UV disinfection [is] a line-of-sight technology, so if anything blocks the UV light, including dirt, stains, anything casting shadows, then those ‘shaded or protected’ areas will not be disinfected.”[xi]

What are our take-aways from all of this? Well, cleaning our tools – washing soil and plant material off our gardening implements – is a necessary first step and probably does a lot to reduce the quantity of microorganisms, too. Next, we probably can’t hit the ten-minute dwell time with paper towels, rags, and wipes, but no matter what products we use, they probably help reduce the population of “garden bad guys,”. In other words, I vow to change my behavior and do something from here on out, knowing that something is better than nothing.

[i] “Cleaning & Sanitizing the Kitchen: Using inexpensive household food-safe products,” Ohio State University Extension (Revised 2010), https://extension.colostate.edu/docs/pubs/foodnut/kitchen-sanitize.pdf . See also, “COVID-19: Cleaning vs. Disinfecting,” https://www.canr.msu.edu/news/covid-19-cleaning-vs-disinfecting, Michigan State University Center for Research on Ingredient Safety (3/23/2020).

[ii] https://www7.nau.edu/itep/main/HazSubMap/docs/HHWaste/DisinfectantsComparisonChart.pdf

[iii] https://ehs.stanford.edu/reference/comparing-different-disinfectants

[iv] Northern Arizona University’s chart, cited at endnote 2: “When mixed with water the solution is only effective as a disinfectant for 24 hours.” The pH of water triggers sodium hypochlorite’s chemical reactions, as explained by Oklahoma State University Food and Agricultural Products Research and Technology Center:  https://extension.okstate.edu/fact-sheets/guidelines-for-the-use-of-chlorine-bleach-as-a-sanitizer-in-food-processing-operations.html (June 2016).

[v] https://ehs.mit.edu/biological-program/decontamination-and-disinfection/ (Quats are “[n]ot active against bacterial spores”); https://ehs.stanford.edu/reference/comparing-different-disinfectants (“Does not eliminate spores, . . . some viruses”).

[vi] https://ehs.stanford.edu/reference/comparing-different-disinfectants

[vii] https://news.engineering.pitt.edu/when-choosing-cleaners-it-helps-to-know-your-chemistry/ . See also Michigan State University Center for Research on Ingredient Safety, cited in endnote 1.

[viii] “Cleaning and Sanitizing the Kitchen,” cited in endnote 1, at pp. 2-3.

[ix] “Does UV Light Actually Disinfect and Kill Viruses?” https://www.bli.uci.edu/does-uv-light-actually-disinfect-and-kill-viruses/ (9/23/2020).

[x] Id.

[xi] Id.