How to Crush Lava Rock: The Definitive Guide

Crushed lava rock can be a game changer when added to the soil in your landscaping. It’s a fertile and porous rock mixed with other ingredients to create bonsai, cacti, and succulent soil. When used as an additive or topdressing soil, plants grow healthy, adding life and color to your home.

Unfortunately, crushed lava rock is too expensive. You’ll need to break the bank to buy the required amount for your garden.

The good news is you can buy large chunks of lava rocks and crush them yourself. But again, crushing lava rock can be tedious and time-consuming. Thankfully, this guide takes you through how to crush lava rock step by step.

Crushing Lava Rock

Lava rock forms after a volcanic eruption and can be available in different sizes. When crushed into tiny particles, lava rock acts as a natural fertilizer. The rocks are rich in iron, magnesium, potassium, sodium, phosphorus, sulfur, and other elements.

Moreover, lava rock creates fast-draining soil thanks to its porosity. It can be a great additive in gardens with poorly drained soil. As a porous material, this rock conserves the water your plants need.

It’s also great for maintaining soil temperature and preventing erosion. Most gardeners and landscapers use lava rock crushed to boost harvest or create healthy, lush gardens.

You can use crushed lava rock for mulching, controlling weeds, and aesthetics. The rocks are available in black, red, or gray, making them an excellent choice for boosting your home’s aesthetic appeal.

If you want to make bonsai soil with lava rocks, crushing them can help save money. Buying crushed lava rocks from the stores will cost you over $30 for only two gallons. Luckily, you can spend less if you buy chunks of lava rock to crush them. Generally, you’ll only pay $5 for a half cubic foot of the natural rock.

If crushing lava rocks sounds like the best idea, read on to understand how you should do it, step by step.

But first, let’s see what’s needed to complete this project.

What’s Needed to Crush Lava Rock?

Below are the tools and materials you need when crushing lava rock:

  • Lava rocks
  • 2×4” wood (4 pieces)
  • Measuring tape
  • Table saw
  • Screwdrivers
  • Screws
  • Screen (1/2” in mesh)
  • Wire cutter
  • Drill machine
  • Sledgehammer
  • Staple gun
  • Hardware cloth
  • Tarp
  • A few buckets (5 gallons each)
  • Eye protector or face shield
  • Broom
  • Dustpan

How to Crush Lava Rock

With everything in your toolbox, you’re ready to start crushing lava rock. So, let’s get started.

Step 1: Make a Wood Frame

To avoid wastage or damage while crushing, you’ll need to make a wood frame for crushing lava rocks.

When making this frame, attach four pieces of 2×4” wood to form a rectangular-shaped frame. Use the measuring tape to ensure you have equal opposite sides. Drill the edges to create holes and secure the frame with screws.

Sand the rough or sharp corners that might hurt you while shaking the frames.

Step 2: Attach the Hardware Cloth and Screen

Take the hardware cloth and cut a piece equal to the wood frame’s lower side. You can use the wire cutter to get the required piece. After cutting, place the hardware cloth on top of the wood frame. Join the hardware cloth and frame together using the staple gun.

Ensure the hardware cloth is a little shorter than the wood frame edges. You don’t want the sharp wires to stab you while shaking.

Step 3: Set the Working Items

This step involves preparing your working area. Spread the tarp on a flat surface and place one bucket on one side of the tarp.

Next, place the wood frame on another side of the tarp. Place the chunks of lava rocks on this frame.

Step 4: Wear Protective Gear

This step is the most ignored when considering how to crush lava rock. Note that the crushing process results in smaller rock particles (shards) that can fly all over. These particles might enter your eyes or hurt your face.

Wear an eye protector such as protective goggles to avoid hurting your eyes or face. A face shield will ensure no rock particles enter your mouth or nose or hit your face.  

If you have protective gloves, wear them.

Step 5: Smash the Large Lava Rocks

Smash the large rocks with the sledgehammer into smaller pieces. Continue smashing them to create smaller particles. The smaller lava rocks will sieve through the hardware cloth and land on the tarp. You can use the edge of the hammer to make the crushing process easier.

Shake the wood frame to let the smaller particles go through the hardware cloth. If large particles remain on the wood frame, keep crushing until everything goes through to the tarp.

If you want to make fine lava rocks, crush the smaller pieces on the tarp using the flat edge of your hammer. These small pieces will break easily, so you don’t need to put much pressure when crushing them.

Step 5: Put the Crushed Lava Rocks in the Bucket

Use the broom and dustpan to sweep and collect the crushed lava rock. Then put the fine rocks into the bucket.

Repeat this process if you have other large lava rock chunks that need crushing.

Is Crushed Lava Rock Different From Uncrushed Lava Rock?

Crushed and uncrushed lava rocks are similar because they’re the same type of rock. However, these two rocks occur in different ways. Lava rock crushed is a product of human actions, while uncrushed lava rock occurs naturally.

Another notable difference is in the look and feel of these two rocks. Crushed lava rock can exist in smaller angular pieces with jagged edges. You can also crush them to make a fine powder.

On the other hand, uncrushed lava rocks are large with smooth textures. They retain their natural shape but might become smooth on the surface due to natural weathering or wear.

crushed lava rock

Frequently Asked Questions

Below are responses to commonly asked questions about lava rocks.

Can you mix lava rock with soil?

You can mix lava rock with soil to correct poor drainage, erosion, and infertility. The porous lava rock ensures proper drainage, maintains moisture, and boosts soil fertility. When used as mulch, lava rocks will prevent soil erosion.

Is lava rock toxic to plants?

Lava rock is not toxic to plants because it’s a naturally occurring substance. However, it can harm young plants, so allow new plants to grow in the normal soil for a few weeks before adding lava rocks. Washing lava rocks before crushing and introducing them to your garden is also advisable.

How long does lava rock last?

Lava rocks in your garden will last at least two years. After two years, the rocks start to deteriorate or show signs of wear, and the nutrients decrease. When this happens, replace or add crushed lava rocks to your soil to keep your plants vibrant.

What plants are best for lava rock?

The best plants you can grow in lava rocks include succulents, dwarf umbrella trees, air plants, orchids, spleenwort, Anthurium, and kangaroo paw fern.

What pH is lava rock?

Lava rock is pH neutral (inert) and doesn’t cause pH fluctuations when added to your garden. However, this is not always the case with all lava rocks. So, test your rocks before adding them to your garden.

Final Thoughts

Hopefully, you’ve learned how to crush lava rock. Ensure you have everything needed in your toolbox to crush the rocks. The lava rock crushing process is tiresome and time-consuming but will turn the rocks into valuable products.