Yes, that’s a very loaded title, we admit. But it’s one we’ve employed to hint at the fact that perlite has some disadvantages which may have never crossed your mind. It’s puffy, crisped rice-like character seems innocent enough. What negative aspects could there possibly be?
We’ll get to that in a moment. But first, you should know we’re not 100% against using perlite. We’re not organizing protests at perlite production sites or anything like that. In fact, we use perlite as an ingredient in our Premium Blend Potting Soil. Our point with this post is to make you aware of some aspects of perlite that might cause you to reconsider your reliance on the product.
What Exactly Is Perlite?
Great question! According to Wikipedia, perlite is a naturally occurring amorphous volcanic glass with a relatively high water content, typically formed by the hydration of obsidian. Perlite’s water content vaporizes when heated to 1,500F, resulting in the material expanding 7-16 times its volume, just like a kernel of popcorn explodes when it is heated. After expansion, it is essentially an inorganic porous rock that will not break down but can lose structure due to compaction. When expanded it is completely white, which is from the reflectivity of its expanded bubbles.
Perlite’s Horticultural Use
Perlite found its way into horticultural use thanks to those expanded bubbles. It can help to lighten soil and reduce soil compaction; i.e. these air bubbles take up space within a volume of soil, reducing soil density. Its porosity helps aerate the soil as well as increases soil drainage. It is also a growing media for hydroponic systems and is an ingredient in some seed-starting mixes.
The Case Against Perlite
So far, perlite doesn’t sound so bad. How could something that improves drainage and aeration and is lightweight (i.e. inexpensive to ship) possibly have negatives?
Perlite does indeed have several cons:
- It’s a non-renewable silica ore product with most of its global reserves being in Eastern Europe and a small percentage here in the U.S. This ore must be mined, crushed and heated to produce perlite. This mining, crushing and heating process requires a major input of energy.
- It’s an inorganic material that does not break down in the soil. Once there, it’s always there, adding very little if anything in the way of nutrition to the soil.
- It floats! Perlite can float to the top of your seed tray, container garden or raised bed if they are inundated with water. And what good does it do there? You’ll have to work it back into the soil, potentially damaging delicate roots systems in the process.
Rice Hulls as a Perlite Alternative
If you’re saying, “You had me at non-renewable” and are now wondering about perlite alternatives, our No. 1 suggestion is to use Rice Hulls. It’s our sustainable alternative to perlite. Our Rice Hulls are grown and processed right here in the U.S.—no mining required. They require much less energy to produce than perlite to bring them to market.
Another perk with our Rice Hulls is that they are an OMRI-listed organic product. Rice Hulls break down in the soil over time and release phosphorus and silica into the soil. These are elements that plants can use! Not only do they replace the soil aeration and drainage functions of perlite with a sustainable product, but they also benefit the plant. And if you are looking for even more benefits of using Rice Hulls, consider this: Scattering Rice Hulls around your plants and on top of your container’s soil will both discourage weed growth and deter fungus gnats. Please check out our product details on the website or bag label to know how much to add for a specific function, (e.g. 0.5-inch layer minimum for fungus gnat deterrent applications and 1-inch layer minimum for weed control).
Be informed and aware of your options. We’re not saying you have to kick the perlite to the curb right this instant. We haven’t yet, either. But when we’re ready to replace perlite in our Premium Blend Potting Soil while maintaining our high standards, we will. Learn more about both products by exploring our online shop.
