Monday, 1 May 2017

Garden Hygiene III: First, sterilise your secateurs....

This is the third of three articles on the subject of Garden Hygiene: the first one covered general hygiene and sensible cleaning of tools; the second covered the hygiene aspects of moving plants: and this one deals with that common advice to Sterilise Your Tools.

Ever read this advice? I have - nearly every book or internet article mentions sterilising (or sterilizing if you can't spell properly) secateurs and other pruning tools "to avoid spreading disease", particularly when pruning roses and fruit trees.

How many people actually do this, I wonder?

Certainly, if you are only gardening in your own garden, then there is no particular need to sterilise at all: and as a general observation, I would point out that a garden is not exactly an operating room, and that spores are in the air, in the soil, on your clothes, on other plants, on passing birds, on the dog...

It's fair to say that if you have one plant which suddenly develops something nasty, then there is definitely a point to cleaning any tools you use on it: but do you also extend that care to the wheelbarrow that you carted the bits away in? The gloves you were wearing as you handled it? The clothes that brushed up against it? How far, exactly, should "one" go? Well, most of us don't worry too much about the peripherals such as gloves and wheelbarrows, but most of us agree that the cutting tool should be sterilised between uses, so as to prevent spreading of diseases from one plant to another. I think the worst advice is for fruit trees, where you will often read that the gardener must "sterilise the blade after each cut". Yeah, right, tell that to someone faced with 500 yards of espaliered apple trees to be pruned. Twice a year.

I did some research, asking my fellow PGG members (Professional Gardeners' Guild) what they did to sterilise their tools: I also asked local gardeners,  people on twitter and facebook, etc, and had some interesting replies, which I'll run though in brief:

1) Wet-wipes: alchohol wipes/detergent wipes/medi-wipes. They seem to be popular, especially among people with  500 yards of espaliered apples, as they are very convenient. Personally I'm really not keen on them, as a one-use non-bio-degradable wipe seems to be about as non-eco as it's possible to get, don't you think? But that's a different discussion.

2) Dipping the blades in a solution of bleach: guaranteed to rust the blades, but no guarantee at all about killing off any pathogens: there seems to be no solid information out there about what strength of solution is required, how long the blades need to be immersed, etc. Some people said a quick dip is enough, some said they left the blades soaking overnight.

3) Dipping the blades in Dettol:  see above.

4) Wiping with Jeyes Fluid. See above.

The funniest response I've had so far is "I stick them under my arm, clamp down and pull forward with an upward arching motion."

Seriously, though, it seems as though everyone has an opinion on this, and I was surprised how many of them said that I "must" do whatever they do, or that their way was "the only" way to do it, or "the only thing that works is..."  although when questioned, it quickly became apparent that not one of them has done any research on it, at all.

It also seems that there is a lot of confusion between cleaning and sterilising/disinfecting: a lot of people use the terms interchangeably, but they are two quite separate actions. "Disinfection" or "sterilisation" in this context is the killing of germs, whereas "cleaning" is the physical removal of germs.

For instance, getting back to those wet-wipes, did you know that you need to use them properly, which means taking the time to actually read the instructions. Disinfection requires the product to be on the surface for between 4 and 10 minutes. It says so on the pack. That means you have to keep re-wiping the surface with more and more wipes, in order to keep it wet for the required length of time. Then you have to let it air dry.

Further research turns up this little gem: articles to be disinfected need to be cleaned first.

What's the difference? I'll keep on saying this: Cleaning means "removing" germs. Disinfecting means "killing" germs.  And if your germs are lurking under a thick layer of organic matter, ie sticky sap, mud, crushed lily beetles and so on, then you need to firstly clean the blades by wiping off all the gunk ("hot soapy water" is usually recommended, but who can find hot soapy water in someone else's garden?), thus cleaning away the majority of germs: and then when the blades are clean, you can disinfect them.

Some sources say "Equipment should be immersed in disinfectant for at least 15 minutes, or according to manufacturers’ instructions" so there does not seem to be any firm answer as to how long it takes to disinfect a tool.

And then there is the vexing question of "how strong is your disinfectant"? Methylated spirits will be effective if it is made up fresh daily and diluted by adding about 3 parts meths to one part water (e.g. add 750ml meths to 250ml water). 70% isopropyl alcohol should be used undiluted. Which one are you using? Do you "make it up fresh" every day? And what about all those other, "own brand" disinfectants?

The answer is to have a look at the bottle and find the active ingredient. Benzalkonium chloride and cetrimide are common active ingredients in what are called "quaternary ammonium compound disinfectants" or quats for short. If you are using a quat, choose one where the active ingredient is at least 5% concentration and use at least one part disinfectant to 20 parts water. (If the active ingredient is less than 5% you will need to use a lot of the product for it to be effective.) You don't need to take my word for this, just look it up on google for yourself.

So how many types of "Disinfectant" are there? We all tend to say the word, without really knowing what we are meaning by it. You may be fascinated to learn that there are seven main groups of chemical disinfectants, as follows:
  • Phenolics such as Lysol or Sudol - these are very effective against bacteria but some are unpleasant to handle or are strong smelling.
  • Hypochlorites such as bleach - these are effective against bacteria but may be corrosive to metal. (Remember what I said about dipping your secateur blades in bleach? That's why.)
  • Iodophors which contain iodine - these are effective against bacteria and some even contain detergents.
  • Alcohol such as methylated spirits - these are effective against bacteria and are generally "fast acting" although it's hard to get a firm answer to the question "how fast?".
  • Quaternary ammonium compounds (quats) such as Savlon - these are generally less effective disinfectants but better as detergents.
  • Diguanides such as Dettol - these have a limited anti-microbial activity and are not suitable to disinfect equipment.
  • Pine fluids such as Pine ‘o’ Clean - these have very little disinfectant activity.

Everything I have read on the internet repeats the advice that "All disinfectant solutions need to be made up freshly each day" so we have to assume that contact with water starts them deteriorating - and for an unstated reason, "tools should not be left soaking in disinfectant", so you can't leave them soaking overnight either.

This is all very confusing, so I decided to stop researching general internet stuff, and go for some proper scientific research.

First I found a scientific Safety Manual which specified recommended disinfectants for laboratory use, which was very interesting: their list of suggested disinfectants only had three entries:

1) Hypochlorites (such as bleach) - Inactivated by organic matter. Corrosive to some metals. May damage rubber. Not compatible with cationic detergents. Working solutions need to be changed daily

2) Alcohols (e.g. 70% industrial methylated spirits) -  Poor penetration of organic matter, and should only be used on physically clean surfaces.

3) Quaternary ammonium compounds (QAC or quats) - Inactivated by protein and some plastics.

See - they also make the point about disinfectants being inactivated by organic matter, and they agree that fresh solution should be made up each day.

After Scientific laboratory research, I made the logical leap to medical recommendations, and took a short tour of their rules and regulations.  Interestingly, the medical world consider the quats (the ones we are most likely to get hold of) to be merely a low-level disinfectant: they are described as "Limited use as disinfectant because of narrow microbicidal spectrum."  They, too, specify that disinfectants must only be used only on clean, rinsed and dried instruments/equipment, because "Protein material, detergent and soap will inhibit some disinfectants." They must also be used in the proper concentration, and within the stipulated lifetime after dilution.

This reinforces our lesson that you have to clean (ie de-gunk) your tools before you even start to disinfect them.

Other lessons learned: The rougher the surface, the longer the contact time required for disinfection (crevices, hinges, worn and pitted surfaces). The number of micro-organisms present will lengthen the time for effective disinfection to take place. In general, higher bioburden requires more time for
disinfection. ("duuuh")  Some micro-organisms are more resistant to disinfection than others. The generally accepted order from the most resistant to the least resistant is: bacterial spores,
mycobacteria, hydrophilic viruses, fungi, vegetative bacteria, lipid viruses.

When it came to trying to find a "best" disinfectant, all I could find was gobbledegook like this:

"Many disinfectants are broad spectrum; that is, effective against all or most forms of microbial life. Some broad spectrum disinfectants include glutaraldehyde, sodium hypochlorite (bleach), and hydrogen peroxide. Non-broad spectrum disinfectants include phenolics and quaternary ammonium
compounds. Alcohols lie somewhere in between these two."

Not so helpful, huh?

Then I read this bit:

"Resistance of micro-organisms depends on the type of disinfectant used. A particular micro-organism may be more resistant to one type of disinfectant than another. For instance, alcohol (isopropyl or ethyl) is effective against vegetative bacteria and most lipophilic viruses, but is not effective against bacterial spores or most hydrophilic viruses."

So what do we actually want to kill, when we sterilise our secateurs? Unless you know what you want to get rid of, you are probably using the wrong product: and either way, you are wasting your time with antiseptic wipes and so on.

One definitive statement is that higher temperatures increase the killing power of most disinfectants, whereas lower temperatures may slow the killing power of most disinfectants, which is no help at all to those of us who work outdoors.

Then it occurred to me that I didn't actually know the difference between "antiseptic" and "disinfectant" and I had been using the two terms interchangeably.

But they are not the same at all - an antiseptic is used on living tissues and cells to destroy any types of infections which may be living on the tissue. Disinfectants are meant to destroy microorganisms which can infect nonliving objects. Common antiseptics include mouthwash, TCP, Dettol, Savlon, Germolene etc.  Things we apply to our bodies.  Disinfectant is stuff like alchohol, the quats we encountered earlier, formaldehyde, chlorine, Hydrogen peroxide, Iodine, Jeyes Fluid etc, (although apparently TCP can also be used as a disinfectant) and are the things we use on worksurfaces, floors etc.

This led me onto Dentistry, as a sub-division of "medical", and I found a study on disinfecting toothbrushes, which showed that Hexidine, 3.0% hydrogen peroxide and Listerine all showed 80-90% efficacy, whereas Dettol showed only 40% effectiveness in decontaminating the toothbrushes. Water, as a control, showed the least effectiveness in cleaning the toothbrushes. So if you want a clean, healthy mouth, soak your toothbrush for 20 minutes in Listerine once a week, then let it air dry. So much for using Listerine as a mouthwash!  My dental hygienist has always said that all mouthwashes are utterly pointless, and this certainly supports her: so rather than using it as a rather ineffective antiseptic, it is actually a quite effective disinfectant (ie to kill microorganisms on things around us).

Oh, and you should replace it - the toothbrush - every 3 months anyway, as the germs will build up on it in that time, to a maximum level.

How is that relevant to us gardeners?  The relevance is that if you are currently using Dettol to disinfect your secateurs, you are wasting your time, change to Listerine!

And what of that old favourite, Jeyes Fluid? It's a disinfectant for outdoor use (according to Wikipedia) and contains: *deep breath*   *outbreak of coughing - it's strong stuff!*

CRESOL -meta
CRESOL -para
Oh, and Tar Acids.   Yummmm, lovely.

Unfortuately, the Jeyes website would not let me see any of their data sheets, but I managed to find them anyway by googling "jeyes fluid data sheets" hehehehe, go on, try it yourself. It's scary stuff, designated as "acute toxicity"  plus warnings about damage to skin, eyes etc.  and whatever you do, don't heat it up and inhale the vapours ("duuuuh!"). However, I can't find any proof of what it actually does, other than the hype on the website with the claims about killing 99% of all known germs, and the claim - concerning the outdoor wipes - that they "provide anti-bacterial protection for up to 24 hours".

Don't forget that the phrase "up to" always includes the possibility of "barely .0003 of a second". And they imply that a single swipe with their wipe will do both of these tricks: kill 99% of the germs, and last for 24 hours.

However, after contacting Henkel, who make Jeyes Fluid, a nice lady called Joan told me that "The instructions for tools is to dilute 10ml of Jeyes Fluid in 5000ml of water, apply to the tools and leave for five minutes before rinsing off."  So much for the outdoor wipes.

I like the loose use of the word "germs", by the way - "germs" is the catchall name for microorganisms ("tiny things") such as bacteria, viruses, fungi, and protozoa, some of which are harmful to us and/or our plants, most of which are essential for normal life.  They act in different ways, they live, breed and die in different ways, and unless we know which type of microorganism we are wanting to kill, we may well be going about it the wrong way. The only thing they seem to have in common is that they flourish in damp environments and die in dry ones, hence the emphasis on letting tools dry out properly.

While we're digressing, let's just ponder for a moment on the likelihood that a wet-wipe of any sort could offer 24 hours of protection.

I have to admit that I get a bit shirty about wet wipes in general (although I use them to clean my hands before I drive off in my car) because stupid people will try to flush them down the loo, where they won't dissolve, and where they clog up the drains. Put Them In The Bin!! Or better still, let them air-dry, then use them again as general wiping-rags. (Stop shrieking about the germs: as just mentioned, germs need a moist environment, so if you let the wipes dry out, they become inert and can be used for all sorts of things in perfect safety.) (no, I wouldn't blow my nose on them,  but they're perfect in the car for cleaning windscreen wiper blades, number plates, lights, etc.)

 The Royal College of Nursing's own document "Wipe It Out" , dated June 2011, investigates the role of medi-wipes: these are non-skin wipes used for the cleaning or disinfection of the patient environment or equipment (detergent or disinfectant wipes) and these are easily available to the general public.

This report said:

"Detergents are essential to the cleaning process, acting to release dirt from a surface.

"Wetness: the ability of the wipe to leave a layer of liquid disinfectant behind on the
surface it is applied to.

"Disinfectant efficacy: once the wiped surface dries, all disinfectant activity stops and,
should any residue of disinfectant be left behind, it will have no effect on further dry
contamination such as microbes (including spores) in dust, which will inevitably settle on
it or be transferred to it soon after cleaning."

Note that they they distinguish between the need for detergent, to clean the surface, and the disinfectant, which needs to be left behind in a layer of liquid.

They comment that the currently accepted European Committee for Standardization (CEN) tests involve a suspension of microbes which is commonly exposed to a disinfectant for up to 60
minutes (the contact time) before looking for an effect. 60 minutes! So if you are relying on a statement in the advertising material of your wet-wipes, which mentions compliance with a stated CEN test (sorry, what was that, your wet-wipes don't comply with any sort of standard? Well, they're going to be pretty useless then, aren't they?) then you need to understand that the CEN test expects your secateurs to be in contact with  your wet-wipe for 60 minutes of wetness to achieve whatever level of germ-killing they are claiming.

Food for thought, eh?!

The report goes on (I did warn you this was a long article, didn't I?):

"As disinfectants in wipes will only work while wet – in other words before they dry on a
surface (usually only a matter of seconds) – the contact time in some tests can grossly
overestimate the level of disinfection that will be achieved by the wipe in practice.
Other tests for wipes can use repeated wiping so that a surface is wet for far longer than
will occur in real-life use. This too will greatly overestimate performance in everyday use."

So, some of the wet-wipe manufacturers cheat in their tests.  Good to know.

"The most common disinfectants used in wipes are chemicals such as alcohols or surface
active disinfectants – quaternary ammonium compounds (QACs) or triamines. These
biocides will achieve limited disinfection (that is with nil or minimal sporicidal activity
or activity against non-enveloped viruses such as norovirus) within the exposure times
that are achieved in practice (typically a few seconds). It should also be noted that the
microbicidal activity will be further compromised if soiling (dirt, vomit, blood, faeces, etc.)
is present.

"Other wipes, usually substantially more expensive, can contain chlorine dioxide or
peracetic acid. These may have activity against spores and non-enveloped viruses, but
again their efficacy will be limited by exposure time, how well the disinfectant is applied to
surfaces (coverage), and the presence of contamination."

The result concludes:

"Wipes are increasingly being used to decontaminate low risk patient equipment or
environmental surfaces. Currently there is no guidance available to support users
or purchasers of wipes and little evidence to support wipes as an effective infection
prevention intervention."

I have read any number of adverts for medi-wipes which say "Kills 99.9% of all germs in 30 seconds and keep working on the surface for up to 4 hours."

In view of everything I have read in the past couple of weeks, I would put forward my opinion that this is simply not true. The 99.9% bit might be, but not the "30 seconds" bit, nor the "keeps working for 4 hours" bit. The data sheets on the individual chemicals are quite clear: in order to kill germs, the surface needs to be clean beforehand, and has to be wetted for 15-30 minutes, and as soon as the surface dries, the killing action ceases.

So, where does that leave us?

Firstly, cleaning your tools is more important than sterilising them:  if you clean off the sap and mud, there is no-where for the germs to lurk.

Secondly, if you really want to sterilise tools, there is no point using a convenient wet-wipe: the blades need to be "wetted", ie immersed in the solution, for the required length of time. The rules are:

1) Follow the manufacturer’s instructions to ensure that the correct (optimum) dilution is used.

2) Make up fresh solution each time, and throw it away once you're done.(I say "throw it away" but I mean "dispose of it safely" of course...)

3)  Check expiry date of the solution. The date should be clearly marked on the container. There is no point using out of date chemicals, they won't be fully effective.

4)  The dunking container must itself be thoroughly cleaned or sterilised every time you use it.

5)  Don't leave containers of disinfectant open - close them asap, and check the pack/bottle to see how long after opening the product is still effective.

6) Always thoroughly clean articles before disinfection, i.e., remove any substance such as dirt, sap, squashed worms and other biological materials.

7) Always allow tools to dry thoroughly after cleaning/disinfecting. This may mean storing them with the blades in the open position.

Thirdly, there is a strong case to be made for not using any anti-bacterial products at all, due to the very real and already existing problem of "super-bugs", ie germs which have become resistant to the anti-bacterials, due to over-exposure. Just type the phrase "Quat-resistant bacteria have been detected in homes routinely cleaned with antibacterial products" and you will find website after website banging on about this issue. OK, most of them are cutting and pasting from each other, but the point remains that using strong chemicals incorrectly (ie not soaking for 5-30 mins as per the relevant data sheet) is no use at all, and using them unnecessarily does more harm than good.

So what do I do? I quite like the principle of  "I stick them under my arm, clamp down and pull forward with an upward arching motion"!

But seriously, in real life, what do I do?

I keep my secateurs (and that includes loppers, choppers, bowsaw, pruning saw, knife, shears, etc) clean  of mud, sap and other plant material. If they get mucky while I am working, I use a handful of grass to wipe them clean. If any of your gardens are infested with Mare's Tails (Equisetum), by the way, then just use a small handful of these: their stems contain silica and they are nature's brillo pad.

If I have been cutting some material that is clearly infected, ie coral spot, any sort of mildew or powdery fungus, or if I've been cutting back plants which I know to have that sort of problem, ie Hellebores, or Roses, then after wiping with grass, I run them under the tap and dry them, before moving on to other plants.

In addition,  I have any number of pairs of secateurs on the go at any one time, so if there isn't time to wash and dry them thoroughly, or if I've found anything nasty in one particular garden, I can put aside that pair for proper cleaning and drying when I get home.

So there you go, phew, that lot took me months to get together, and although in a way it is depressing reading (ie you're doing it wrong, wet-wipes don't work, and doing it "properly" is a right faff) it is better to know the facts than to blithely continue with a regime that is ineffective.


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  1. haha! brilliant! thank you for the work you have put into this! it has always been my intuitive and semi knowledgeable belief that disinfecting on the go is a bit of a myth. As you say both the time it needs and what you are concerned about. You could also have mentioned that many plant disease are ubiquitous in the environment and will happily infect your plants regardless of your pruning. Apple Canker typically infect via leave scars. I've actually found a link to this being stated in 1921! Yet the idea that we must disinfect our secateurs in case we spread Apple Canker remains strong almost 100 years later!
    Saying that! I teach a class of 20 students and I think wipes has a place there, bio-degradable ones! Sure it would be better if i could provide everyone with a nice rag but the wipes are well just easier. They will clean off sap and help make sure that the blades cut cleanly. And actually that is the crucial bit. If we are worried about infection, clean, as small as possible, cuts are important! So worry about sharp blades as much as disinfected blades imo! Thanks again. Glyn

    1. Glyn, you are most welcome: it's one of those subjects where "most" people just do what "everyone else" does, and never query it.

      And you are so right about the diseases being ubiquitous - I must go back and add something to that effect *frantic typing sounds in the background*.

      I'm interested to hear that you get your students to de-sap their blades, I wouldn't have thought about that. I teach mine how to sharpen their blades with a pen-file, and the demo does actually include the comment that you can "feel" once you've cleaned off the dirt and sap, the penfile starts to "grip" and that's when sharpening begins.

      It hasn't occurred to me that I should teach them to clean the blades before they start sharpening them - but I will in future! I don't think I'll encourage them to use wipes of any sort (there are too many non-biodegradeable ones out there) but I will certainly instruct them to go and find some mare's tails (Equisetum)!!

  2. Thank you for your advice I just wondered did you look at a disinfectant for hairdressers for those occasions when you want to disinfect your tools I know one brand claims to prevent rust.

    1. Yes, I did include disinfectant for hairdressers in the research: the chemicals recommended for hairdresses are no more effective than those used medically.

      You are right, there are a couple that claim not to promote rust formation - which is not the same as preventing rust - but I couldn't find any supporting evidence for that claim.

  3. Thanks so much for your hard work. Everyone can benefit from your diligence. I'm going yo start rose pruning today and you know what? I'm just going to buy a new pair of secateurs, dedicate them to the one job and then follow your advice about cleaning.

    1. Glad to hear it! I'm sure your roses will appreciate a pair of lovely new, super-sharp secateurs - and it's much easier to keep a new pair clean than it is to try to clean an old, rusty, pitted pair.

      Besides, it's nice to have new tools now and again!

  4. Thank you so much for researching and sharing this! Much appreciated

  5. This is exactly the info I was looking for, but didn't expect to find do well researched and summarised. This must have taken you aaaagges! Thank-you. All makes sense, dare I say sounds like common sense, however I'll probably continue to wipe clean my secateurs with an old flannel and alcohol between plants whilst working as explaining all of this to disbelieving customers isn't going to pay my way! Own brand supermarket vodka in a reused water bottle is my product of choice. Anyone else?!
    Thanks again Rachel

    1. Hi Rachel (*waves bottle of vodka while wobbling on top of a ladder*) yes, it did take aaaaages but so worth while, I thought. I'm glad you found it useful.

      I am laughing hysterically at the thought of using vodka - if I tried that, my Trainee would probably be trying to drink it! (that's a joke, intended to convey a humourous self-deprecating knowledge of how hard it must be for my Trainee to have to listen to me for four hours at a time!)

      Of course, now that you know the true effectiveness - or not - of all these products, you could just as easily use plain tap water in an re-used bottle with "Sterilising Alchohol" written on it, thus saving money!!

  6. Thank you so much for sharing. Little knowledge is dangerous knowledge as they say.

  7. Great article! Thank you. On television I saw a professional grower dipping their secateurs in milk inbetween cuttings prevent infection. How does that work (does it work?) by trapping viruses / bacteria or by killing them? They were a proper professional growing thousands of cuttings.

    1. Hi Peter,

      I have never heard of dipping blades in milk to prevent infection, and a fairly cursory internet search does not reveal any mention of such a thing, so I have no idea!!

      On the face of it, it seems a ridiculous thing to do: milk is itself full of pathogens - you only have to leave a cup of milk sitting outside the fridge for a couple of days to see how "germy" it is. So I can't think of any logical reason to use it in gardening.

      It is entirely possible that this is one of those awful "received wisdom" practices, of which I so disapprove: you know, where someone does something just because "it has always been done this way". They might have been taught to use milk by someone who didn't know why they used it: they might have mis-read something somewhere: it might be that they tried it once and it seemed to work, so they've continued with it ever since!!

      I really don't know. But it's not something which I will be trying for myself!

  8. This post has suddenly gained new readership, thanks to the Covid problem: I had a comment from Marisa (*waves*) pointing out that people are doing the quick 2-second wipe on supermarket trolley handles etc, and thinking that's going to protect them from C-19.

    Well, trolley handles shouldn't be covered with organic matter, they're smooth inert plastic, so they should be a lot easier to clean: and again, I would point out that there is a difference between cleaning - physically wiping off the "germs" - and sterilising, which takes a long time.

    So do continue to wipe your trolley handles: but keep your hands away from your face while you're shopping, and remember to clean your hands with gel as soon as you leave the shop: again, after you've loaded your (contaminated) shopping into the car, again once you've unloaded it at home, and again before eating.

    It's not easy, being clean....


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