What Is Perlite Made Of: When and how to use it

You will have seen perlite when you open up a bag of compost, all the little white specks mixed throughout the compost are pieces of perlite. In this article you will find out what perlite is made from, how, why and where you should use it in your garden.

What is perlite

Perlite – also known as expanded pyrite, is a form of amorphous volcanic glass, it is naturally occurring and is very lightweight and porous when processed. It is beneficial to use in gardening as it will keep your soil well aerated and drained and its porous nature helps to store nutrients.

What is perlite made of

Perlite is a form of volcanic glass which has a high water content, typically formed from the hydration of Obsidian. Perlite in its natural state is like a rock/glass. It is and brown/ black in colour before processing.

Processing is carried out by heating the rock/glass to very high temperatures- 1560-1650 Fahrenheit (850-900 Celcius) this causes the moisture inside the glass to turn to steam and expands the material from 7 to 16 times its original size- this steam expansion turns the perlite from a dense dark rock into a fluffy white lightweight product which we associate with the perlite we know. The material turns white due to the reflection of light bouncing off the surface of the expanded bubbles. Its nickname volcanic popcorn is well deserved!

How to use perlite in your garden

The main uses for perlite around my garden is for drainage. Because perlite is an expanded glass material it will not compact. When you add it to your soil or compost it keeps the soil structure from closing up and becoming dense.

Dense compacted soil will hold water within its structure and prevent the free movement of water through it, thereby stopping drainage. As mentioned before perlite can also help to hold vital nutrients within its cavities for your growing plants. A similar product- vermiculite can be used in the garden although it has very different properties.

Where to use perlite

Perlite can be added to potted plants, raised beds or mixed in with the soil in the ground. Perlite is a very useful and can be used in all applications around your garden and home. It allows the roots of the plants to grow uninhibited and provides a clear path for water air and nutrients to get easy access as the soil is not compacted, worms and other insects can enhance the soil further.

Perlite in hydroponics

Large or coarse grade perlite is very useful in hydroponics as a growing media and is great for starting stem cuttings as it allows the roots of the plants to uptake water and nutrients without becoming water saturated or getting root rot. See our article on how to use perlite in hydroponics.

What types of perlite are there?

Perlite usually comes in three size grades, fine, medium and coarse.

Coarse perlite is used more often in deeper soil cultivations such as raised beds or if the soil has strong water holding characteristics – clay soils etc.

Medium grade perlite is used more in larger potting applications or window boxes, fine grade is only really used with seed starting mixes or cutting mixes.

There are no hard and fast rules which grade you should use- if you are unsure and it is your first time to use it, a medium grade will usually be ok for most applications.

Where can I buy perlite?

You can buy perlite at any local gardening centre or home and garden store – or you can buy online.

I have listed the types i would recommend below. Click on the image or title for more information on Amazon.

Espoma PR1 1 Cubic Foot Organic Perlite

GROW!T GROWT JSPERL84 Perlite, 4 cuft 4 cuft White

Bonsai, Cactus & Succulent Pumice – Professional Sifted and Ready to Use American … (2.5 Dry Quart

If you have any questions please let me know in the comments section below. Thanks!

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