How to Crush Lava Rock? (Step By Step Guide)

If you are not familiar with the word lava rock, then you might be wondering what it is used for and why would anyone need to even crush it.

Well, lava rocks are hard soil structures that are formed from being near a volcanic eruption. And due to their forming process, the rock particles are very fertile, porus, and are filled with a lot of air.

And the best thing about this volcanic soil is, it releases the excess water to the plants slowly as much as the plant needs. 

Why Crush Lava Rocks?

Lava rocks are a wonderful choice for any plants and especially the bonsai trees because this soil can hold up much more moisture than most other garden soils.

Since bonsai soil is very expensive in the market, this soil can offer you a cheaper solution, saving a lot of money for you if you are willing to put up with the work for just this once. 

For instance, if you go to a store to buy crushed lava rock then it will cost you about more than 30 dollars for just 2 gallons of it.

But if you can get your hands on natural products then you can get half a cubic foot of lava rock just for around 5 dollars. But the biggest issue here is, you have to crush it on your own. 

And, here comes this article to help you out with everything you need to know to crush them in the easiest way like a pro. So, without making any delay let’s get this show on the road–

What Things Do We Need to Crush the Lava Rocks? 

To crush these lava rocks by yourself, your toolbox needs to have the following things:

  • Lava rocks
  • Sledge hammer
  • Table saw
  • Measuring tape
  • 2×4 inch wood (4 pieces)
  • Drill machine
  • Screwdrivers
  • A face shield and an eye protector 
  • Screen (½  inch in mesh)
  • Some screws
  • Wire cutter
  • Staple gun
  • 4 Buckets ( 5 gallons each)
  • 1 roll of hardware cloth

Before starting to work you have to make sure that you wear enough safety precautions.

Like face shields and protective goggles because the crushing process will produce enough small pieces of shards that can get inside your eyes or hurt you in the mouth within a second. 

After getting all the mentioned things, now let’s get into the main process:

A Step-by-Step Guide to Crush the Lava Rocks

Step 1:

First, we’ll take the 4 pieces of 2×4 inch wood and make a shape of a rectangular tray by joining all of them together, and later we will use this frame to crush our lava rock.

After joining the pieces make sure you sand the rough corners very well so that they don’t hurt you while shaking the frame in the future. 

This frame will help you to keep the lava rock pieces in one place and filter through it rather than spreading them everywhere with hammer strokes.

Step 2: 

After outlining the frame and taking measurements with the help of measuring tape, you have to cut the screen according to the size of the frame with the help of a wire cutter.

And then attach the screen tightly to the wooden frame with the help of a staple gun.

Step 3:

When the wood frame is attached to the screen you have to place it over the buckets so that when you crush the rocks the pieces will fall directly into the bucket through the screen and larger pieces will be left stuck in the screen to be crushed again.

Step 4: 

Now that everything else is ready, it’s time for you to place the large lava rock over the frame which is already on top of the bucket, and start to smash them hard so that it separates them into two or three large pieces.

Step 5:

Take a large piece and keep smashing it with a sledgehammer until you get smaller crushed pieces of even size. Whenever the bucket gets filled, empty the bucket and shift the crushed lava rocks in another place.

Additional Step

You can do another additional step to get even more fine crushed lava rocks. In this case, you have to spread the uneven crushed pieces in a tarp and take the flat edge of a small hammer and work your way through it. 

You won’t have to put much pressure on it as the pieces are already half crushed and will crumble easily this time. You can use a broom and sweep them out with a dustpan and shift them to your garden or wherever you like.

However, this whole process will take a few hours but in the end, you will get your desired fine powdered crushed lava rocks more than enough in amount to use for your beautiful bonsai trees and all other plants in your whole garden.

Frequently Asked Questions (FAQs)

Is lava rock toxic to plants?

Lava rocks can be sometimes poisonous when the plants are very young. So, before using you have to wash them very thoroughly and make sure the plant has survived a few weeks in normal soil first.

How long do lava rocks last?

Lava rocks last for about 2 years without any problem. But after a couple of years, it starts to deteriorate and the particles start to break down naturally. Moreover, the nutrient supply capacity also keeps decreasing. In this case, it needs to be replaced so that the plants keep up with their nutrient requirement.

Does lava rock attract termites?

Since lava rocks are very light-textured and porous soil, it keeps the earth warm and makes a good home for termites. So it can definitely attract termites at times.


Crushing the lava rocks can be a very tiresome process so take your time, have enough breaks or crush them up every day a little, whatever seems convenient to you because all you have to do is smash the hammer on them over and over again.

I hope this method proved to be very helpful for you as this is the most practically efficient and easy way of manually crushing the lava rocks.

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