What is perlite and should you be using it in your garden?
As perlite becomes increasingly popular, this is a question that more and more gardeners are now asking.
The answer is…
If you’re looking for a way to boost root growth, provide insulation, and drastically improve drainage, then perlite is something that you should definitely be looking into.
Ever bought a potted plant and noticed little white balls in the soil?
That’s probably perlite. It may look like styrofoam, but perlite is actually a naturally-occurring mineral that is used as a soil additive, as well as for several other purposes in various different industries.
If you’re still not convinced, take a perlite particle and crush it between your fingers. Perlite will break down into a gritty substance, while plastic will simply squash inwards.
Perlite is lightweight, inexpensive, easy to use, and can have a number of benefits in the garden:
- Acts as a natural filter, allowing excess water to drain away while retaining just the right amount of moisture and nutrients for your plants.
- Increases aeration in the soil. This allows for more oxygen to reach the roots, enabling them to grow stronger and healthier. Better aeration also means more room for beneficial insects.
- Helps to prevent soil compaction, keeping it fluffy and healthy.
Perlite is a type of volcanic glass, created when erupted lava quickly cools. In its natural form, it’s actually quite heavy, dense, and rock-like, and is black or gray in color, rather than white.
After being extracted, perlite goes through a crushing and heating treatment. This causes the perlite to expand and pop, resulting in those little white balls.
It may not look like much, but perlite has a very interesting chemical composition. Many of its natural chemicals can provide additional benefits when used in the soil, not only to the plants but also to the soil itself:
- Silicone dioxide
- Aluminum oxide
- Potassium oxide
- Sodium oxide
- Magnesium oxide
- Iron oxide
- Calcium oxide
Perlite is mined and processed in 35 countries around the world, with Greece recently surpassing the United States of America as the biggest producer of perlite. Hungary, Turkey, China, Armenia, and Japan are also actively extracting their natural perlite stores.
In order for a material to be organic, it needs to have come from the earth and not have been processed in a significant way.
Perlite meets these criteria, which is why it has been certified as an organic material by the USDA.
After perlite has been treated and processed, it is separated into four different types, based on the size of each particle.
Generally, the coarser the perlite, the better it will improve drainage. However, finer grades of perlite have their place in the garden too…
Although fine perlite won’t make a huge difference when it comes to drainage, it’s great for starting seeds and rooting cuttings – you’ll notice faster and stronger root production.
Fine perlite is also a good option for those looking to aerate a lawn. Simply sprinkle it over the surface of the grass and allow the rain to slowly push it in.
Unfortunately, fine perlite isn’t as widely available as other perlite types, so you may need to look for specialist stores.
Medium-grade perlite is a good option for potted plants, because its size means that it blends in quite well with the soil. It can either be mixed with other soil components or used alone.
Coarse perlite is generally considered to be the all-purpose type of perlite. It can greatly improve drainage while retaining water. It is also large enough to resist being blown away by strong winds.
While super-coarse perlite may be the best when it comes to increasing drainage and aerating the soil, the size of these particles is pretty large. They can sometimes be a third of an inch in size, meaning that they don’t blend in well with finer soil mixes.
As mentioned earlier, perlite is used in other industries too, meaning that you may occasionally come across other types of the material.
Expanded perlite is commonly used in construction, while coated perlite is sometimes available too. While these have their uses, horticultural perlite is the only type that you should be using in your garden.
- The heating process it undergoes renders perlite completely sterile, meaning that there’s no chance of it passing on any diseases to vulnerable plants.
- It contains a number of natural minerals, including potassium oxide, magnesium oxide, and calcium oxide, that benefit plant health.
- Since it doesn’t break down in the soil, it can be reused after it has been rinsed. If your perlite has come into contact with diseased plants or soil, it is easy to sterilize and then use again.
- It has a neutral pH (between 6.6 and 7.5), so won’t interfere with acidic or alkaline soils.
- It doesn’t contain any chemicals.
- It provides plants with some added insulation.
- It doesn’t absorb nutrients from the soil, or from water when used in a hydroponic system.
- It retains its shape in the soil, even when wet.
- It is relatively inexpensive compared to other materials that produce similar results.
- It is resistant to rodents and termites.
- Easily available at garden centers, and due to its low density, can also be easily ordered online.
Although natural and organic, perlite is non-renewable, meaning that it won’t be around forever.
Perlite can sometimes blow away in strong winds or float away in excess water due to how lightweight it is.
Doesn’t help with water retention – you may need to water plants more often than if you weren’t using perlite.
Large amounts of perlite dust can cause breathing and eye problems, making precautionary safety gear needed. The dust can also interfere with the tubing and pumps in hydroponic growing systems. If using perlite on a small scale, you can avoid this by mixing some water into the bag of perlite as soon as you open it, which will reduce the amount of dust you’re exposed to.
This video sums up nicely the Pros and Cons of Perlite:
There are two main ways in which perlite can be used in the garden…
Making your own soil mixes allows you to meet the specific requirements that individual plants have. Some may require a sandy and acidic soil while others may prefer a richer, alkaline soil.
Either way, most plants thrive when given the right amount of drainage, making perlite a good addition to soil mixes.
The amount of perlite you use in a soil mix should depend on what you plan on using the mix for.
However, around 10% to 20% perlite is usually ideal. You can increase this if you wish, going up to 50%, or even 100%, but the more perlite you use, the fewer nutrients will be available to your plant.
In addition to perlite, and depending on what your plant requires, other components that you could add in to your homemade soil mix include:
- Peat moss
- Mature compost
If you would like to improve the drainage of existing beds or lawns without having to manually mix perlite into the soil, then use perlite on the surface.
A surface sprinkling of a fine grade perlite will slowly work its way deeper into the soil, where it will boost drainage and increase aeration.
However, don’t do this on a windy day – fine grade perlite is susceptible to being blown away by strong winds.
Perlite is known for being one of the best hydroponic growing mediums available. Here’s how to use it…
While perlite can be used on its own for hydroponic growing, this does limit you when it comes to the type of system you can use. Since perlite is so lightweight, any system that sees water directly interacting with the perlite would be a no-go. All of that water would simply cause the perlite to float and wash away.
Instead, perlite works best in a high-water hydroponic system when it’s combined with other growing mediums. Ideally, these should be heavier and larger, allowing them to hold the perlite in place. Some good options include:
Rooting cuttings in water is a popular propagation method, but for stronger roots, use perlite instead.
Particles will need to be moistened first, and then placed into a small pot. Insert a cutting into this and keep it lightly misted – you don’t want the perlite to dry out. The roots that your cuttings grow will be much stronger and more vigorous than if you had used water alone.
As an added bonus, when it comes time to transplant your cuttings, you’ll find that they are easy to gently pull away, without damaging that delicate new root system.
Considering vermiculite as an alternative to perlite?
The two are often confused, which isn’t surprising since they have quite a few similarities – both are natural minerals extracted from rock.
However, vermiculite particles retain more moisture than perlite, which means that they aren’t as effective at improving drainage. On the other hand, vermiculite would be a better option for plants that thrive in damper soils.
Perlite and vermiculite can actually work well when used together. A combination of the two will give you a soil mix that:
- Retains plenty of moisture for your plants
- Absorbs and retains nutrients for your plants
- Easily drains away excess moisture
This video talks more about Perlite vs Vermiculite:
Pumice is another naturally-occurring material that is used to improve drainage and aerate the soil.
However, unlike perlite, pumice particles are very large. This makes them a good choice for expansive areas of heavy, clay soil, especially since their size will also prevent them from being blown away.
For the home garden, perlite is usually a better option than pumice.
Otherwise known as DE, diatomaceous earth is a naturally-soft rock that is available in powder form for gardeners. It is often used as a pest control method.
Just like vermiculite, DE retains high amounts of water, and so doesn’t do much for improving drainage.
DE is also known for the way in which it tends to clump together when it’s wet, which can actually inhibit airflow and root growth.
Drainage and aeration are 2 aspects of gardening that are often overlooked, but with severe consequences…
Good drainage and aerated soil are two of the basic needs shared by nearly every plant out there, and perlite allows you to easily achieve this. Just this one simple addition to your soil can give you plants that are healthier and so much more productive.
Whether you’ve just got a few potted houseplants, expansive vegetable beds and grassy lawns, or are setting up a hydroponic system, understanding what is perlite and how to use it could be a game-changer when it comes to how you grow.