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Halloween science: Pumpkin decomposition

9 Comments Toddler, Preschool, Kindergarten, 1st Grade

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What does your family do with your jack-o-lanterns after Halloween is over? Most years we just throw them away. But last year we decided to do use our jack-o-lantern do some some Halloween science.  An old jack-o-lantern was perfect for showing the kids the process of pumpkin decomposition. Decomposition, also known as rotting, is a process by which organic substances are broken down after death. Eventually, decomposition breaks organic matter down so that it becomes part of the soil again.

Note: You can find more Halloween activities on my Halloween Activities for Kids page.

Halloween Science - pumpkin decomposition || Gift of Curiosity

So a few days after Halloween last year, we made the decision to NOT throw out our jack-o-lantern. Instead, we put our already-starting-to-rot pumpkin into an unused gardening box.

Halloween Science - pumpkin decomposition || Gift of Curiosity

As you can see, even at the one week post-carving mark, the pumpkin was already starting to mold inside.

Halloween Science - pumpkin decomposition || Gift of Curiosity

At the two week mark, the inside had turned black. Further, the pumpkin had started to shrivel and was beginning to collapse on itself.

Halloween Science - pumpkin decomposition || Gift of Curiosity

And at the four week mark, it had shriveled up. By observing this process, the kids were getting a good sense for the process of pumpkin decomposition.

Halloween Science - pumpkin decomposition || Gift of Curiosity

We actually let the pumpkin sit outside for several months. It eventually turned into a flat, hard item that was barely recognizable as a former jack-o-lantern. Sadly, I failed to get any pictures after the 4 week mark, and eventually one of the kids tossed it in the garbage. But we may just give this pumpkin decomposition experiment another go this year to see how it turns out.

If you plan to do this activity, you may also enjoy reading the book Pumpkin Jack by Will Hubbell. It is the story of a boy who carves a jack-o-lantern for Halloween, and then leaves it to rot in the backyard. By springtime, little was left of the jack-o-lantern, as it had mostly decomposed. But then a pumpkin vine began to grow where the jack-o-lantern had rotted, so the life cycle continued.

More pumpkin resources for kids

More pumpkin posts from Gift of Curiosity:

  • Books about pumpkins
  • Describe a pumpkin using all 5 senses
  • Pumpkin decomposition experiment
  • Pumpkin math: Measuring the circumference of a pumpkin
  • Pumpkin arts and crafts
  • Pumpkin do-a-dot printables
  • Printable pumpkin outlines
steam-kids-halloween-collage-rev
Looking for more Halloween projects that incorporate Science, Technology, Engineering, Art, and Math (STEAM)? Then you’ll love STEAM Kids Halloween.This e-book includes 50+ pages of spooky fun STEAM activities that will wow the boredom right out of kids!


You can find more Halloween activities on my Halloween Activities for Kids page and Halloween Activities for Kids Pinterest board. 

Follow Katie @ Gift of Curiosity’s board Halloween Activities for Kids on Pinterest.

Filed Under: Toddler, Preschool, Kindergarten, 1st Grade, Halloween, Science, STEAM Tagged With: decomposition, pumpkins

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Reader Interactions

9 Comments

  1. Stephanie

    October 28, 2013 at 6:21 am

    I love your science experiments! If I can convince hubby we may try it this year too! Thanks for the idea!

    Reply to this comment
  2. Natalie

    October 29, 2013 at 9:36 am

    We did it this year with a piece of pumpkin I saved from making pumpkin cookies. It led to some interesting discussions with my 7 year old about cremation vs burial 🙂 Thanks for sharing with Afterschool!

    Reply to this comment
  3. Anna@The Measured Mom

    November 1, 2013 at 11:21 am

    Love this — funny because we do it without even trying. The kids notice every day at how our outdoor pumpkins are rotting… glad they’re getting some science learning in too 🙂 Thanks for sharing at After School!

    Reply to this comment
  4. Carrie Sturges

    November 2, 2013 at 5:25 am

    I have done this with my kindergarten class for the last twelve years. Another variation that I do is putting a few slices of a pumpkin inside a glass jar for inside observation. Decomposition takes a little more time, however, it is fascinating to see what happens over time in a space that they can safely touch. If you choose to do it in a jar, make sure you use a glass jar so it doesn’t smell. Plastic jars tend to share the smell of the decomposition process. Also, to help the process, you need to open the container every week or few days to let air in. You may want to do it outside.

    Reply to this comment
  5. Ashley

    November 6, 2013 at 5:28 am

    Allowing it to sit and rot is a great experiment! Featured you on Mom’s Library this week!

    Reply to this comment
  6. Kerry

    September 20, 2014 at 7:37 am

    I used to teach at a school where a colleague would bury a jack o’ lantern, some newspaper and a foam cup. Later they would dig them up and have a talk about decomposition and its implications.

    Reply to this comment
    • Katie SG

      September 20, 2014 at 2:20 pm

      What a fun activity for kids! I wonder how a pumpkin would decompose in the ground compared to above the ground. It might be time to try a new experiment this year!

      Reply to this comment
      • Missy

        October 23, 2014 at 6:17 am

        Hi Katie,

        I have also done a journal where my 4K kiddos draw a picture in a “journal book” and then I write their words. It is a fun way to document what they are seeing over a period of time.

        Missy

        Reply to this comment
        • Katie SG

          October 23, 2014 at 10:19 am

          What a great idea to extend the learning!

          Reply to this comment

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I help parents who are transitioning into homeschooling shed old mindsets and embrace their homeschooling superpowers so they can create a homeschool they love where their children will thrive.

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