Friday, January 26, 2018

What Natural Cleaners Kill Germs Best? A Homeschool Science Experiment


When I get ready to order curriculum and supplies before the start of each school year, I like to sit down with my daughter and ask what she would like to learn about that year. I like her input, children tend to be much more eager about learning when it's something that interests them. This year she asked to learn about germs so we ordered  a kit called The World of Germs from The Young Scientist's Club's Magic School Bus series (you can check them out here). The last several projects in the kit involved growing bacteria on agar in petri dishes. She had so much fun, she wanted to do more, so we ordered some prefilled agar petri dishes from Amazon (you can order your own here) and decided to design a few of our own experiments. The first thing she wanted to try was testing which of our household cleaners killed germs best and so we set out to design a simple experiment to figure it out.


Our Experiment: Which Natural Cleaners Kill Germs Best?

First we gathered up our usual household cleaners; white vinegar, hydrogen peroxide, homemade essential oil spray ( eucalyptus, rosemary, clove, and lemongrass essential oils in distilled water), and castile soap and water.  Then I had her write a hypothesis and we set up our experiment.  The petri dishes I ordered come pre filled with agar (bacteria growing medium) so there's no preparation, they come ready to use. We taped off two equally dirty sections of my kitchen counter and labeled them A and B.

Then we split a petri dish in half by drawing a line down the center with a permanent marker and labeled the sides A and B. Using a sterile cotton swab (that came with the petri dishes we ordered) we swabbed area A on the counter and gently smeared it all over side A on the petri dish. Then we cleaned area B on the counter with white vinegar and let it dry. Using a fresh sterile swab, we then swabbed area B and smeared it on side B of the petri dish. We replaced the petri dish lid and then  it was time to let our bacteria grow. We created our own incubator by putting warm water bottles in a large pot with a lid. We set the petri dish inside and put it in a dark cupboard for a few days, replacing the warm water bottles every few hours to keep the bacteria warm. After about 3 days these were our results:

Side A (our control) grew lots of bacteria. Side B, the side cleaned by vinegar grew only a few colonies. Vinegar appears to be a fairly effective cleaner!

I had her record the results both by drawing a picture and counting and recording numbers of colonies. Then we repeated the experiment 3 times for our other 3 cleaners.

Results from our "what natural cleaners work best experiment"


Our Results

They all appeared to kill most bacteria. Hydrogen peroxide worked the best. Not a single bacterial colony grew on it's side of it's petri dish! 

The essential oil spray was our least effective cleaner, which inspired our next experiment, Do Essential Oils Really Kill Germs and Which Ones Kill Germs Best?

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  1. What a fun kit and experiment! My kids would love this!

    1. It was definitely a fun experiment, my daughter really enjoyed it :-)

  2. What a fun experiment. Good to know that about E.O. I hope your kids had a fun time and learned something.

  3. Great that you ask your daughter what she would like to study... good idea! Interesting results - thanks for that information. :)

  4. I posted your post to my Facebook page :)

  5. Oooh, interesting! Oils are so popular as cleaners these days, too!

    1. Thanks for reading! I was a little surprised that oils appeared to perform the worst.

  6. What a cool idea! I know inspiring people to test bacteria probably wasn’t the main point of this post but now I want to do it with my boys!

    1. You should do it! It was such a fun way to learn about bacteria!


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