How Do Crystals Grow? A Salt, Epsom Salt and Sugar Experiment for Kids

Growing crystals is a patient, rewarding experiment. Kids set it up in ten minutes, then check on it every day for a week. By the end, they have shiny proof that tiny invisible particles can build something you can hold.

What you need

Table salt (pickling or kosher salt gives clearer crystals, but any works)
Epsom salt (plain, no scent or colour)
White sugar
Very hot water from a kettle (grown-up only)
Three heat-safe mugs or jars, labelled
Shallow dishes, dark paper if you have it, and cotton string

The method

A grown-up pours hot water into each mug and stirs in the solid, one spoonful at a time, until no more will dissolve. Each mug gets a different ingredient.
Let it cool, then pour a little of each clear solution into a shallow dish. For a string crystal, hang a piece of string into a jar of solution.
Place the dishes in a spot where they won’t be bumped, such as a windowsill or shelf.
Check daily. Draw what you see and measure the largest crystal.

What to expect

Within a day or two, small crystals appear at the edges of the dishes. Epsom salt makes long, needle-like crystals. Table salt makes small cubes. Sugar makes bigger, slower crystals and can take more than a week, so patience is part of the lesson. Humidity matters too, and results vary by home, so tell children that’s expected.

The science

When salt dissolves in hot water, its particles spread out between the water molecules. Hot water holds more dissolved solid than cold. As the solution cools and the water slowly evaporates, there’s less water to hold the particles. They start to find each other and line up in a repeating pattern. That pattern is a crystal.

The flat faces and straight edges of a crystal are a clue to the neat arrangement of particles inside. Different substances stack differently, which is why each makes a different shape.

Fair-test ideas

Evaporation speed. Put one dish on a warm windowsill and another in a cool room. Which grows crystals first?
Seed crystal. Drop a tiny crystal in a solution. Does it grow faster than one started from nothing?
Different salts. Compare crystal shape, size and the day they first appeared.

Questions kids ask

Is this a chemical change? No. Dissolving and crystallising are physical changes. You get the same substance back.

Can I eat them? No. Treat all of them as experiment materials, including the sugar.

Why did the string crystals grow on the string? The string gives the particles a rough surface to start on.

Safety

The hot water is for a grown-up to handle. Keep dishes away from pets and young children, and wash hands afterwards.

Next steps

Our lesson How do crystals grow? has the full steps. It’s part of Earth and Sky at Home with a rainbow lesson and a cloud-in-a-jar. For a classroom look at dissolving, try Where does the salt go when it disappears in water? Sign up for three lessons free.