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What is Perlite? Uses, Benefits & Common Alternatives | Almanac.com

What is Perlite? Uses, Benefits & Common Alternatives

potting mix with perlite and a yellow shovel
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The Pros and Cons of Perlite: A Gardener's Guide

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You have probably noticed the little white chunks in commercial potting soil and wondered what they were and why they were there. They are often mistaken for pieces of Styrofoam, but are much harder. Actually, it is perlite, a natural stone that is added to the soil mix to improve drainage. Keep reading to learn about perlite and tips for using it in your garden!

What is Perlite?

Perlite is a volcanic stone with a high water content, that starts life as porous volcanic glass. When heated to 1600 degrees F, the rocks expand up to 20 times their original size, giving it one of its nicknames—volcanic popcorn. Like popcorn, it is very lightweight and porous.

After heating, the popped rocks are crushed to smaller sizes ranging from fine to medium and coarse, depending on the manufacturer. It is sometimes given a grade number, with #4 being the largest at 1 inch in diameter. 

preparation of soil substrate for planting houseplant into a pot
Consider adding perlite to your potting mix to increase aeration.
Credit: RESTOCK Photos

The Many Uses of Perlite

Perlite is loved by gardeners for its ability to improve drainage and aeration. Along with being lightweight and porous, perlite is non-toxic, clean, sterile, and disease-free. It has a neutral pH, doesn’t expand, rot, or shrink, and is certified for use in organic gardens.

When perlite is added to soil or a soilless potting mix, it improves drainage by providing space for water and air to flow. Mix it half and half with potting soil for propagating cuttings or seed starting. It is also a great medium for rooting, cutting, or starting seeds and will prevent damping off. Learn how to make your own soilless potting mix.

You can also sprinkle a light coating of fine perlite over seeds that need light to germinate. It allows light in while keeping them moist. Check out our guide to seed planting success.

For gardening, look for horticultural perlite, which can be large to medium grade with 1/2–inch—1/8-inch particles. Coarse grade or extra-large perlite with particles larger than ½ inches is perfect for orchids, succulents, and other plants that require good drainage. 

In construction, perlite is added to plaster or mortar to lighten them up. Finer grades can be used in filters or as fillers, and larger grades can be found in stormwater filtration systems. 

The Pros and Cons of Using Perlite for Planting

Reasons You Might Choose Perlite for Your Garden
Pros of Using PerliteCons of Using Perlite
Lightens up heavy soilConsidered a non-renewable resource
Improves airflow and drainage Dusty (wear a mask when using it)
Sterile and neutral pHIt may contain trace amounts of fluoride
Prevents seedlings from damping offHas no nutritional value for plants

Should I Use Perlite or Vermiculite?

Perlite is especially good at drainage by providing channels for water and air to flow through the soil. It absorbs very little moisture, making it great for aeration for potting plants that need dry conditions, such as succulents, cacti, and some orchids.

Vermiculite is also good for drainage and aeration, but does its best work providing a steady supply of moisture. It can expand and hold water like a sponge, releasing it as plant roots need it, making it perfect for use with plants that need moist soil. Learn more about vermiculite.

You can also have the best of both worlds! If aeration and moisture retention are both important to you, you can use both perlite and vermiculite together.

Perlite offers a unique and versatile tool for gardeners. While it may not be a perfect solution for every plant, its ability to improve drainage and aeration and prevent root rot makes it a valuable addition to many potting mixes. Whether you’re starting seeds, repotting succulents, or simply looking to lighten up heavy soil, perlite can be a secret weapon in your gardening arsenal.

Do you have more questions about perlite? Leave them in the comments below!

About The Author

Robin Sweetser

Robin has been a contributor to The Old Farmer’s Almanac and the All-Seasons Garden Guide for many years. Read More from Robin Sweetser

2023 Gardening Club