How to Grow Epsom Salt Crystals 2

Epsom salt crystals readily absorb food coloring.
Epsom salt crystals readily absorb food coloring. (Jason D)

Epsom salt crystals are among the safest and easiest crystals to grow. The natural crystals are clear, but they readily accept dye from food coloring. Here’s what you need to know to grow these crystals yourself.

Epsom Salt Crystal Materials

All you need is Epsom salt, water, and a bit of food coloring if you want color. Epsom salt is another name for magnesium sulfate (MgSO4), but the crystals incorporate water to form magnesium sulfate heptahydrate (MgSO4·7H2O). Epsom salt is an inexpensive, non-toxic salt that is readily available in pharmacies for bath salt and agriculture stores as a soil treatment. It forms monoclinic crystals that can assume a variety of shapes, but most often look like crystal shards or needles.

  • 1/4 cup Epsom salt (magnesium sulfate)
  • 1/2 cup water
  • Food coloring (optional)
  • Shallow bowl
  • Sponge (optional)

While you can grow the crystals in any container, they tend to grow as a mass. Removal is much easier if the dish is shallow or has a wide mouth for easy access to the bottom of the container.


  1. Heat the water to boiling in the microwave or on the stove.
  2. Stir the Epsom salt into the hot water until the solid is fully dissolved. Add food coloring, if desired.
  3. If there is floating sediment or some undissolved solid, pour the liquid through a coffee filter or paper towel. Use the liquid to grow the crystals. Take care to avoid getting burned (adults should do this step).
  4. Pour the liquid over a piece of sponge or into a shallow container.
  5. The shape and size of the crystals depends on their growing conditions. Larger crystals grow if the container is placed in a sunny location, where the temperature is warm and evaporation concentrates the liquid. These crystals may take a few hours to a couple of days to grow. Quick crystals grow when the liquid cools quickly, as in a refrigerator. Chilling the liquid produces smaller, delicate-looking crystals. Refrigerating the liquid usually produces crystals within 30 minutes to a couple of hours.

Tips for Success

  • Epsom salt crystals tend to be fragile. Growing them on a sponge gives them more surface area so they can grow more quickly and are easier to handle without breakage.
  • If you’re not happy with your crystals, you can re-grow them without starting from scratch. Simply heat the the crystals and their liquid until the solid dissolves and try again. You can add a little more water if all the solid won’t dissolve.
  • If crystals aren’t growing, it usually means the solution isn’t saturated. You can increase the concentration of the liquid by blowing a fan across the top to speed evaporation. Another option is to place an undissolved crystal from the package into the liquid to act as a seed crystal. If you have a magnifying glass, it’s interesting to compare the shape of the tiny crystals to the larger ones that you grow.
  • These crystals are easy to preserve. Once you remove them from the liquid, simply allow them to dry and display them. They tolerate a coating of clear nail polish or other sealant, although the crystals are too soft for use in jewelry, except perhaps earrings or pendants.

Natural Sources of Epsom Salts

The natural form of Epsom salt (MgSO4) is a mineral called epsomite. A common hydrated magnesium sulfate mineral is kieserite (MgSO4·H2O). The mineral meridianiite is another hydrate of magnesium sulfate (MgSO4·11H2O). Magnesium sulfate also occurs on other worlds besides Earth. Scientists believe Mars has deposits of kieserite in the canyon Valles Marineris, while meridianiite was found by NASA’s Opportunity Rover at Meridiani Planum. The bright spots of the dwarf planet Ceres are believed to be reflected light from magnesium sulfate hexahydrate.


  • Büchel, Karl Heinz; Moretto, Hans-Heinrich; Werner, Dietmar (2000). Industrial Inorganic Chemistry. John Wiley & Sons (2nd ed.). ISBN 9783527613335.
  • De Sanctis, M. C.; Ammannito, E.; Raponi, A.; et al. (2015). “Ammoniated phyllosilicates with a likely outer Solar System origin on (1) Ceres.” Nature. 528 (7581): 241–244. doi:10.1038/nature16172
  • Genceli, F.E., Lutz, M., Spek, A.L., Witkamp, G-J., (2007). “Crystallization and characterization of a new magnesium sulfate hydrate MgSO4•11H2O.” Crystal Growth & Design, 7, 2460–2466.
  • Odochian, Lucia (December 1995). “Study of the nature of the crystallization water in some magnesium hydrates by thermal methods.” Journal of Thermal Analysis and Calorimetry. Vol. 45, No. 6. doi:10.1007/BF02547437

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2 thoughts on “How to Grow Epsom Salt Crystals

    • Anne Helmenstine Post author

      There isn’t a set number of crystals. Rapid cooling produces numerous smaller crystals. Slower cooling results in fewer larger crystals. Or, you can select one crystal as a “seed” (removing all the others) to maximize its size.