How to Grow a Cup of Quick Crystal Needles

Green Crystal Needles
These crystal needles grew within a few minutes in the refrigerator, but it might take an hour or two, depending on your conditions.

Grow a quick cup of crystal needles in your refrigerator. The whole project takes between 15 minutes and 2 hours, from start to finish. All you need is Epsom salt, water, and a little food dye if you want a pop of color.


  • Epsom salt (magnesium sulfate)
  • Water (hot from the tap)
  • Food coloring (optional)
  • Clear glass or jar

Epsom salt is sold either in the pharmacy section of a store or near soap (bath salt). It’s an inexpensive salt that appears as clear crystalline chunks or a white powder. It’s also available scented, but you just want the basic stuff for this project. While many crystals exclude dye as they grow, magnesium sulfate readily incorporates it. So, it’s easy to color the crystals using food coloring, but if you dye the liquid it may be too dark to observe the crystals unless you remove them. You can use any small cup or jar for this project, but if it’s clear you can monitor progress easily.

Grow Crystal Needles

  1. Mix equal parts Epsom salt and hot water. If you use 1/2 cup of salt, dissolve it in 1/2 cup water.
  2. Stir the Epsom salt in water for about a minute. What you’re doing is making a saturated solution. There should be some undissolved salt at the bottom of the container. If all the salt dissolves, add a bit more.
  3. Place the container in the refrigerator. The cup will fill with crystal needles as the liquid cools. Depending on how saturated your solution is, this could take from 15 minutes to 2 hours.

Tips for Success

Epsom Salt Crystal
You can take a single Epsom salt crystal and put it in the salt solution to grow a large single crystal. (Peter Corbett)
  • Use hot tap water and not boiling water. The rate of cooling affects crystal size and shape. If the water starts out too hot, the crystals will resemble threads more than needles. Water temperature also determines how much salt will dissolve.
  • If you know you’ll want to remove the crystals from the container, place a bottle cap or coin on the bottom. This serves as a base and makes it easier to remove the crystals without breaking them.
  • Don’t drink the liquid. Magnesium sulfate isn’t toxic, but too much is bad for you.
  • You can remove a crystal and place it in a fresh solution to grow a large single crystal. The first crystal is called a seed crystal. It provides a surface for new crystal growth.
  • This type of water absorbs and releases water, so it’s not well-suited for keeping as a specimen. If you want to keep the crystals, leave them in their liquid and seal the container so water can’t evaporate. The crystals will dissolve and reform as the temperature changes (sort of like a storm glass). If you have your heart set on crystals you can keep, try another crystal-growing project.

Epsom Salt and Epsomite

Epsomite is a mineral form of magnesium sulfate that forms thin needles.
Epsomite is a mineral form of magnesium sulfate that forms masses of thin needles. (Manuel Pina L)

Magnesium sulfate crystals that you grow are actually a magnesium sulfate hydrate. What this means is that water gets incorporated in the crystal matrix. The crystal structure depends on how much water is bound to the salt. In nature, magnesium sulfate crystallizes to form the mineral epsomite, which has the formula MgSO4·7H2O . Epsomite and Epsom salt get their name from Epsom in Surrey, England. Epsom is the place where the mineral was first described in 1806. The heptahydrate (7 water molecules) forms colorless, white, or pastel orthorhombic crystals. Epsomite absorbs water from the air, loses a molecule of liquid water, and changes into magnesium sulfate hexahydrate (6 water molecules). The hexahydrate has a monoclinic crystal structure. Epsomite crystals form needles, spikes, and fibrous sheets.


  • Büchel, Karl Heinz; Moretto, Hans-Heinrich; Werner, Dietmar (2000). Industrial Inorganic Chemistry (2nd ed.). John Wiley & Sons. ISBN 978-3-527-61333-5.
  • 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, Volume 45, Number 6. doi:10.1007/BF02547437