Finding what is best for your garden is going to start with the results of what others have done successfully.
Volcanic rocks are known for being great for soil, but when it comes to pumice or lava rocks for plants, which ones are better?
Pumice and lava rocks have very similar soil properties, both rocks will improve the soil structure to improve drainage and airflow. Lava rocks are cheaper and more available, plus lava rocks will also deliver different benefits and advantages for use.
Aren’t They Both Lava Rocks?
They are both volcanic rock, but pumice and lava rocks are really different types of rocks!
One easy way to identify them is their colors.
Pumice is a light color, generally white or cream colored and lava rocks are dark colors from red to black.
How Is Pumice Formed
Pumice is formed when a volcano erupts explosively and causes the magma to become agitated and froth.
If the magma cools before the bubbles have a chance to escape the froth, pumice and bubbles are trapped in the magma.
Pumice is special because unlike other types of volcanic rocks like vermiculite and perlite, pumice needs no processing treatment to get the rock ready for your gardens.
It can be mined from the earth, crushed in to smaller sizes and is packaged and sold.
How Is Lava Rock Formed
Like pumice, lava rock is a volcanic rock that does not need processing treatment, lava rock is different than pumice because it is not made from magma.
Lava is the molten rock that makes it out of the Earth and once this lava cools, you have a type of lava rock. Once the lava rocks cooled, they are mined and crushed into pieces small enough to pack and be sold.
Advantages
What can volcanic rock do for your gardens? A lot.
Pumice and lava rocks are both held in very high regard as being the “best” soil amendments. Let’s take a look at both.
Pumice
Pumice greatly enhances soil structure. It adds size to the soil so it does not compact together as easily. However, pumice is a rock and will not degrade like other additives will.
A good soil structure means a good drainage and airflow for your plants. Good drainage and airflow means an increase in beneficial organisms in your soil, especially if you are outdoor gardening.
Pumice is porous, because of those froth bubbles. And these pores retain water, which makes pumice great for water retention.
When your soil dries out and your plants need water, they can pull water from the pores of the pumice which in effect will mean you won’t have to water as often.
Lava Rocks
Lava rocks function differently. Lava rocks can also amend the soil, or they can also be used as a base for a paved road, or much the same or even simply for decoration.
Like pumice, lava rocks are very porous and have similar effects on soil. They can improve the structure of the soil, improve drainage and airflow, as well as very good for holding onto and retaining water.
One thing that lava has that pumice does not, is that it holds and absorbs heat quite well.
This may seem like an odd advantage in a gardening sense, but lava rocks are used for mulch, and during the day when the lava rocks lay dormant in the sun, they will soak up heat during the day, and release it overnight so that as many plants can stay warmer at night.
This is especially nice with potted plants that you bring in during the winter. Having that pocket of heat at night, allows them to last a little longer outside without bringing them in.
Therefore, the weight of lava rock is an advantage;
- The lava rocks are heavier than pumice;
- The mass of lava rock also means they are less of a risk of blowing away (or being transported in wind);
- Lava rocks stay so put, they are often referred to as a base under access roads or underneath driveways.
Price and Availability
One key factor to pumice is the way in which it forms. Pumice forms when a volcano is violent enough to create froth within the magma.
Since not all eruptions are violent enough to agitate magma enough to create pumice, pumice is also not guaranteed to form.
Pumice Cost
Since pumice is never guaranteed to form, and yet there is still high demand for pumice from gardeners, there is a good chance pumice will cost you more than lava rock. You may also have encountered availability issues from pumice.
Pumice is not solely utilized for the purpose of gardening, and you may find pumice in your life every day without even knowing it. Pumice can be found in:
- Kitty litter;
- Erasers;
- Filters;
- And even cosmetics!
Lava Rock Price
Lava rock on the other hand, can occur at any moment that lava reaches the surface of the earth and sets- which is almost guaranteed to happen with a volcanic eruption in some capacity.
Whether it is a small eruption or giant explosion will determine what amount of lava is erupted, and what kind of harvest of lava rocks can be made, erosion of the lava rock means you won’t run into supply issues getting lava rock.
There are plenty of retailers offering lava rocks for whatever you need product. These retailers include hardware stores, gardening centers, and online. Since there is no treatment for your lava rocks to use in your gardens, lava rocks are fairly inexpensive.
Final Thoughts
Well there you have it. Pumice is lighter- both the weight, and the colour is lighter if you were considering colour in your gardens. If you were not considering light colour, our recommendation would be lava rock.
Bags (or wholesale bags) of lava rock will be cheaper, you can find lava rocks easier, and there are many more uses of lava rocks than just a soil amendment!