Garden Myths Gardening Gardening tools

Sterilizing Pruning Tools: Don’t Use Bleach

By Larry Hodgson

Most gardeners know that it’s important to disinfect pruning tools (pruning shears, saws, loppers, etc.) before moving on to another plant. And that, if you’re removing diseased branches, tools should likewise be sterilized between each cut as well. It is, in fact, very easy to transfer a disease from one plant to another or even from an infected part of a plant to a healthy part via contaminated tools.

And it is also wise to clean and disinfect pruning tools before putting them away for the winter.

However, contrary to popular belief, bleach is not the product of choice for sterilizing metal tools.

To give the devil it’s due, bleach will indeed kill microbes when applied to cutting tools. The problem is it has other less interesting effects.

  • Bleach is corrosive and will damage the tool, causing rust and pitting, forcing you to sharpen it more often and probably to replace it far earlier than should have been necessary.
  • A tool damaged by bleach has a pitted surface that can become infested with microbes that sterilization efforts will no longer reach, possibly transmitting diseases from plant to plant in spite of your best efforts.
  • Bleach is a skin irritant and can also cause serious damage to the eyes. 
  • Bleach can stain and ruin your clothes if you spill any … something likely to happen when you’re outdoors pruning.
  • If you attempt to clean the cutting surface with a cloth or a cotton ball dipped in bleach, it will quickly disintegrate under the bleach’s oxidizing effect … as will your gardening gloves.
  • Bleach is highly phytotoxic and can damage the cells of the branch you’re pruning.

In other words, use bleach for washing clothes and possibly, well diluted, for sterilizing pots, but keep it away from both plants and gardening tools.

Better Than Bleach

There are commercial liquids specifically designed to disinfect pruning tools and they work fine. Your local garden center almost certainly carries them. However, you probably already have perfectly good sterilizing products in your home right now and they will cost you much less.

The best and cheapest is probably rubbing alcohol (isopropyl alcohol). You can dip the tool in a small cup of it or wipe the blade with a cotton ball or cloth dipped in it. It cleans (it’s very good at removing sticky conifer sap) and sterilizes, yet is in no way corrosive. 

Hand sanitizers, readily available everywhere these days, cost a little more than isopropyl alcohol, but sterilize just as well. If you carry a bottle of sanitizer around with you anyway, look no further! You already have what you need!

Other readily available home products that sterilize well without harming tools include Lysol, Pine-Sol and Listerine. Use the original formula, not one of the multitudes of offshoot products of unconfirmed effectiveness.

But don’t use vinegar to clean and sterilize tools. Although you’ll see a cloth soaked in vinegar recommended a sterilizing for garden tools on Facebook and elsewhere on the Internet, it’s not a good choice. It simply doesn’t kill that many microbes, including some very harmful to plants, and therefore won’t give you the sterile tool you need. And it actually feeds some microbes!

Other Helpful Hints

  • It’s better to let the blade dry before making another cut, or to wipe it dry with a clean cloth, because even the products mentioned above, although less phytotoxic than bleach, can damage otherwise healthy tissues on the next branch to be cut. This is one of the reasons alcohol and hand sanitizer are such good cleansers/sterilizers: they evaporate very quickly, even almost instantly and so the tool is soon dry.
  • To avoid transferring germs from one plant to the next, make sure that your tool is always sharp, since a dull blade will have pitted edges in which microbes find refuge from your sterilizing treatments.
  • Finally, never apply disinfectants (alcohol, sanitizer, Lysol, etc.) directly to the wound. In the past, it was believed that wiping a tree wound with a disinfectant would help prevent future fungal infections. Today we know that it can instead kill plant cells designed to help cut surfaces heal over … leaving the wound more susceptible to fungi! Mother Nature provides plant wounds with natural protections against this type of infestation. It’s best just to let them do their job!

Text based on an article originally published in this blog on December 14, 2015. 

4 comments on “Sterilizing Pruning Tools: Don’t Use Bleach

  1. In this post Covid age many of us have large stockpiles of hand sanitizer. If I understand you, I can move a bottle into my garden toolbox. Do I need to wipe off excess or simply let it dry?

  2. I use my shears more than anyone, but do not sterilize them. Disease simply is not a problem for much of what I work with. Sterilization is only done when pruning material with certain diseases or the likelihood of such diseases. Unfortunately, the fruit trees are susceptible to a few diseases, so shears get sterilized in between individual trees of the same type.

  3. maureenedden8212

    A very useful tip. Thank you.

    • Yes, good to know. I have been using bleach to sanitize my shears. Thanks for the great advice!

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