How to Grow a Crystal Rainbow

Learn how to grow a crystal rainbow. This is such a fun STEM experiment for the kids. Perfect for both rainbow fun and learning.

Do you want more activities? See our list of Colorful Rainbow Activities for Kids.

Now that spring is here, it’s time to start thinking about sunshine and all things rainbow. This is why we love this simple crystal rainbow activity. It’s a fun way for kids to create an experiment that also looks really cool and engaging.

If you’re looking for a super fun science activity for the kids, don’t miss out on this one! It’s a super exciting way to grow your very own rainbow! We always do this activity during the spring months, and it’s a lot of fun!

The kids look forward to this every single year, and they really never get tired of this activity! It’s one that you can easily do in a short amount of time as well.

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Interesting Rainbow Facts for Kids

Before we even started our rainbow crystal project, I shared a few fun facts with my kids to get them curious. These aren’t your usual rainbow tidbits—they really got my kids asking questions and noticing rainbows in new ways.

• Rainbows can appear double, with a second, fainter arc called a secondary rainbow that has its colors reversed.
• Sometimes you can spot a “supernumerary rainbow,” which is a series of extra pastel-colored bands inside the main arc caused by tiny uniform water droplets.
• There are “moonbows,” which are rainbows that show up at night when moonlight reflects through water droplets (they’re pretty rare but so cool to learn about).

Recommended Rainbow Books

I also keep a short list of rainbow-themed books handy that work well with this activity. They’re a great way to keep the learning going and tie in storytelling with science.

Rain Before RainbowsHow the Crayons Saved the RainbowThe Rainbow Beeall about RAINBOW: Encyclopedia Book for kids age 5 and upRainbow: Ready-to-Read Level 1 (Weather Ready-to-Reads)Did You Know? The Rainbow Edition

 

Why do kids need to learn about crystals?

When I introduced crystals to our homeschool science time, I honestly didn’t expect it to hold my kids’ attention for long. But once we got into growing our own crystal rainbow, they were completely focused.

Crystals are a great way to explain how solids form, how solutions work, and even how time and temperature affect physical change. Plus, there’s something magical about seeing those tiny structures grow right before you—it turns abstract concepts into something real and hands-on.

But it’s more than just a science experiment. Activities like this helped my kids learn to follow instructions, be patient, and stay curious about the world around them. Crystals opened the door to so many follow-up questions—about minerals, rocks, even the science behind rainbows themselves.

Who says you have to wait until the rainbows happen outside when you can easily make your own rainbow at home?

If you love this activity, be certain to check out our Rainbow Foam Dough as well.

What is the purpose of growing crystals?

This activity is for fun! It’s also a great way to introduce a simple science experiment to the kids. This will demonstrate to them that hands-on learning is a great deal of fun!

Ensure that the kids document what they think will happen. This can be as simple as establishing the steps they believe will occur.

Have them develop a simple thought process of what they think will happen as each hour passes, so that they can see how it changes over time.

Recommended Rainbow Toys

Over the years, I’ve found that having a few open-ended rainbow toys on hand helps keep the creativity flowing after we finish our science activities. These are great for reinforcing color recognition, sequencing, and allowing kids to explore patterns and structures in their way.

40-Piece Wooden Rainbow Stack Set, 4-in-1 Building Blocks preschoolers Early Development & Activity Toys Montessori Toys for Kids 3, 4, 5, 6 Years and Older Gifts for Boys and GirlsJust Play Slinky the Original Walking Spring Toy, 5-inch Diameter Plastic Rainbow Giant Slinky, Fidget Toy, Kids Toys for Ages 5 UpZMLM Scratch Paper Art-Crafts Gift: 2 Pack Rainbow Notebooks Supplies Toys Easter Basket Stuffers for 3 4 5 6 7 8 9 10 Years Old Girls and Boys Kids Birthday Party Games (Pink)Skillmatics Magnetic Matching Activity – The Alphabet Rainbow, Preschool Learning Toy & Game for Kids, 35+ Magnetic Pieces, Gifts for Girls & Boys Ages 3, 4, 5, 6Galt Toys, Rainbow Lab, Science Kits for Kids, Ages 5+, MulticolorGanowo 12 Pack Wacky Tracks – Rainbow Color Snap Click Fidget Toys for Kids Adults ADHD Finger Sensory Autism Stress Relief Keeps Fingers Busy and Minds Focused

 

Do crystals continue to grow?

They won’t, but it’s fun to try out that theory with the kids! Have them make notes of what it looks like and then compare it again the next day. This is a simple activity for them to take notes and pay attention to.

Supplies needed for this Rainbow Crystal

• water
• Borax detergent booster
• Chenille Stems
• Scissors
• Deep, wide-mouth jar or glass
• Thread/thin string
• Popsicle sticks

How to grow a crystal rainbow?

Make sure to let the kids help out with this. Be present for parental supervision, but have them assist with the steps.

Most of these steps are super simple and are great for the kids. They’ll start by twisting the different-colored stems together, so make sure they do that to begin the project.

If they’re having trouble with this step, show them the visual below. Some kids are visual learner,s and this might be just what they need!

Part of this activity will have to be done on the stove, so this is where you come in as the parent. Boil the water and be careful around the kids. You’ll also have to pour this into a jar, so be very careful with this as well.

Pour in the mixture slowly so it doesn’t break or crack the glass.

How long does it take to grow a crystal rainbow?

This is a quick process. They’ll start making crystals almost immediately, but you’ll want to give them at least 24 hours to fully complete the process.

You’ll notice that once that timeframe is up, the growth of the crystals is done.

Are borax crystals safe?

While this is a great learning project, ensure that the kids don’t try to put it in their mouths. It’s not safe for them to eat or ingest.

Why didn’t my borax crystals work?

If the activity failed, the water mixture likely wasn’t hot enough. Ensure that your water is sufficiently hot for the borax to dissolve.

What would happen if you put borax crystals back in hot water?

This could be a super fun experiment. Find out what would happen if you put the crystal rainbow back into the hot water.

Would more crystal rainbows start to grow? Or would it wash away the current rainbow crystals? You’ll have to see to find out!

Be cautious when performing this part of the experiment, as you will be handling hot water again.

More Rainbow Activities

• Rainbow STEM Activities
• Rainbow Science Experiments
• Rainbow Slime Recipe
• Rainbow Foam Dough
• Watercolor Rainbow Process Art by 3 Dinosaurs
• Rainbow With Pot of Gold Craft by Simple Everyday Mom

This activity is a fun and low-preparation way to introduce science at home. It’s simple enough to do with young kids, but packed with learning opportunities that can lead to meaningful conversations and deeper exploration across subjects.