Mom, you know all about dirt, dontcha? Today, we’re going to talk about the SCIENCE of dirt! Or rather, the science of soil, a vital resource to farmers and gardeners. I have a fun STEM recipe to make your own edible “soil” with your kids. Lucky for me, my kid is a fourth grader and is currently studying plants–so this recipe fit in nicely with his school work. Plus, it’s not every day you get to eat your science experiment!
FYI: this recipe is part of Monsanto’s Science Camp, a project to get kids excited about science and STEM. Watch the video below for a quick science lesson on soil and more info on the experiment.
Edible Dirt Recipe
You will need:
- A clear plastic cup or juice glass
- a zip top bag
- rolling pin or mortar and pestle
For your soil layers, you will need different kinds of snack foods to represent rocks and dirt.
- Sprinkles for Organic Matter and Microbes
- Gummy Worms for Decomposers
- Dark Cookies for Topsoil
- Light Cookies for Subsoil
- Chocolate Candies for Bedrock
You can use whatever ingredients you like. Mitch and I used honey and chocolate graham crackers for the subsoil and topsoil, Whoppers for the bedrock, mini M&M for the organic matter and sprinkles for the microbes. And of course, some gummy worms.
Start your experiment by filling the bottom of your cup with “bedrock.” In real life, bedrock in the dense, hard rock typically hidden by layers of dirt and sediment hundreds or thousands of feet thick. Not the bottom of the world like in Minecraft. If you need to brush up on your geology, and you have an older kid, check out Geology of Missouri from Washington University.
Missouri contains each of the three classes of rocks that forms the basement rock and bedrock: igneous, metamorphic, and sedimentary rocks. The most common igneous rocks in Missouri are rhyolite, granite, diabase, and volcanic tuff, each of which can be seen exposed in the St. Francois Mountains.
If you’ve taken the kids to Johnson Shut-Ins, you’ve played on exposed bedrock!
Anyway, I used Whoppers for my bedrock, and Mitch went for giant chunks of chocolate graham crackers. You just need to cover the bottom of your cup with your bedrock.
Subsoil is the huge layer of dirt and rock that sits on top of the bedrock. Plants with deep roots can reach here, like soybeans and sunflowers. We’re going to represent subsoil with light colored cookies that are roughly crushed. Just crumble them with your hand, leaving nice big chunks. Mitch, rebel that he is, used the M&Ms for his subsoil. I think he just wanted to eat a lot of them…
Topsoil is the most important layer of dirt, and also the thinnest–only a couple inches deep. This is the rich layer of soil where all the nutrients, minerals and organic matter are, and where you plant seeds. The grass in your yard is planted on topsoil. We’ll represent this with dark cookies, finely crushed. I used chocolate graham crackers, and Mitch used the honey graham crackers.
To get your topsoil just right, put it in a plastic bag and crush it into a powder with a rolling pin. You can also use a mortar and pestle if you have one.
Now the worms!
Topsoil is home to all the little worms and bugs and grubs that break down organic matter in the soil. They pretty much make the topsoil, so let’s give them a big thank you! We’re going to use gummy worms to represent…well, worms.
And a pinch of Organic Matter
Organic matter is the leaves and decomposing critters that dissolve into the soil. It’s not pretty, but the worms eat it up and plants love it. We’re going to represent this with mini M&Ms.
Don’t for the microbes! This is the beneficial bacteria you’ll find in topsoil that plants need so much. Use sprinkles to represent your microbes.
Once you’re done creating your soil layers–get a shovel, er, spoon, and dig in! This is the one time it’s ok to eat dirt!
Oh, and in case you’re curious…Mitch decided his dirt sample need plants. So he fashioned “trees” from sticks of graham crackers and marshmallows.