Make Baking Soda Stalactites and Stalagmites

homemade baking soda stalactites and stalagmites
Anne Helmenstine

Stalactites and stalagmites are large crystals that grow in caves. Stalactites grow down from the ceiling, while stalagmites grow up from the ground. The world's largest stalagmite is 32.6 meters long, located in a cave in Slovakia. Make your own stalagmites and stalactites using baking soda. It's an easy, non-toxic crystal project. Your crystals won't be as big as the Slovakian stalagmite, but they will only take a week to form, instead of thousands of years!

Baking Soda Stalactite & Stalagmite Materials

  • 2 glasses or jars
  • 1 plate or saucer
  • 1 Spoon
  • 2 Paper Clips
  • Hot Tap Water
  • Piece of Yarn, about a meter long
  • Baking Soda (Sodium Bicarbonate)
  • Food Coloring (optional)

If you don't have baking soda, but you can substitute a different crystal-growing ingredient, such as sugar or salt. If you want your crystals to be colored, add some food coloring to your solutions. You might even try adding two different colors to the different containers, just to see what you get.

Grow Stalactites and Stalagmites

  1. Fold your yarn in half. Fold it in half again and twist it together tightly. My yarn is colored acrylic yarn, but ideally, you want a more porous natural material, such as cotton or wool. The uncolored yarn would be preferable if you are coloring your crystals since many types of yarn bleed their colors when wet.
  2. Attach a paper clip to either end of your twisted yarn. The paper clip will be used to hold the ends of the yarn in your liquid while the crystals are growing.​
  3. Set a glass or jar on either side of a small plate.​
  4. Insert the ends of the yarn, with the paper clips, in the glasses. Position the glasses so that there is a slight dip (catenary) in the yarn over the plate.
  5. Make a saturated baking soda solution (or sugar or whatever). Do this by stirring baking soda into hot tap water until you get so much added that it stops dissolving. Add food coloring, if desired. Pour some of this saturated solution into each jar. You may wish to wet the string to start the stalagmite/stalactite formation process. If you have a leftover solution, keep it in a closed container and add it to the jars when needed.
  6. At first, you may need to keep an eye on your saucer and dump liquid back into one jar or another. If your solution is really concentrated, this will be less of a problem. Crystals will start to appear on the string in a couple of days, with stalactites growing down from the yarn toward the saucer in about a week and stalagmites growing up from the saucer toward the string somewhat later. If you need to add more solutions to your jars, be sure that it is saturated, or else you will risk dissolving some of your present crystals.

The crystals in the photos are my baking soda crystals after three days. As you can see, crystals will grow from the sides of the yarn before they develop stalactites. After this point, I started to get good downward growth, which eventually connected to the plate and grew up. Depending on the temperature and rate of evaporation, your crystals will take more or less time to develop.

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Your Citation
Helmenstine, Anne Marie, Ph.D. "Make Baking Soda Stalactites and Stalagmites." ThoughtCo, Apr. 5, 2023, Helmenstine, Anne Marie, Ph.D. (2023, April 5). Make Baking Soda Stalactites and Stalagmites. Retrieved from Helmenstine, Anne Marie, Ph.D. "Make Baking Soda Stalactites and Stalagmites." ThoughtCo. (accessed June 2, 2023).