Perlite, easily recognizable as little white rocks, is both cheap and easy to use, which is why you should reconsider using it to grow your plants. Perlite was one of the first reliable hydroponic growing mediums available to the horticulture market. You have seen it in the form of hard white bits in potting soil, but perlite can be used by itself in many hydroponic systems.
You can find varieties of perlite in liquid filtration systems, insulation and even soap. Growers add it to soil and soilless mixes to reduce compaction and increase drainage and aeration. The manufacturing process involves heating the raw material until it pops like popcorn, thus the porous nature of horticultural perlite.
I work in the gardening industry, and it’s my job to test different growing products and methods. (Discover some other options in Finding a Happy Media: Soilless Grow Media Tips & Tricks.) In an effort to familiarize myself with all possible scenarios, I continue to experiment with various soil blends and all the latest and greatest hydro substrates. While perlite is often a component of these mixes, there are also benefits to using perlite by itself.
Benefits of Perlite
Unlike most growing mediums, perlite starts out neutral in pH. There is no rinsing or buffering required in regards to correcting pH. Simply adjust the solution and water it in. Perlite will take on the acidity or alkalinity of the liquids that saturate it. Even when rinsed and dried, the naturally occurring pH of 7.0 isn’t going to harm a typical indoor garden plant species.
While it’s true that perlite is a non-renewable resource (volcanic rock), the supply on our planet is quite extensive. The current amount is expected to last hundreds of years. For me personally, environmental concerns are also a factor in choosing perlite. It’s super easy to reuse! Recycling this medium is simpler than most others currently available.
Perlite doesn’t hold onto nutrients the same way as soil, rockwool, coco coir, or even clay pebbles. You can reuse any of those mediums if you choose, but perlite can be cleaned in a matter of minutes, not days. When removing root balls, the medium falls away gently with a shake. Simply remove all visible organic matter (mostly roots) and rinse the perlite until the runoff measures less than 150 ppm.
If you need to sterilize the used perlite, just soak it in a 10% bleach solution. After 20 minutes of soaking, rinse thoroughly. Rain, dehumidifiers and reverse osmosis filters are always the preferred sources for rinse water. Actually, those are the best sources of water for most indoor garden applications.
There are even more benefits of using perlite in your grow space. It is one of the cheapest growing mediums you can find. It’s so lightweight that you can easily lift four cubic feet of it without straining. Plus, perlite is a staple in both traditional and hydroponic gardening, so you can find it at most garden supply stores. All of the above factors make perlite very easy to acquire.
Drawbacks of Perlite
Now for the bad news. Perlite is messy. You don’t need to rinse it before mixing with soil, but you wouldn’t want all that dust in a hydro system. Perlite dust is not just a problem for pumps and tubing, but also for your respiratory system. It is listed as a “nuisance dust,” which means it can aggravate your eyes, mouth, throat and lungs.
Perlite is not considered carcinogenic, although the main component (alumina silicate) is. The research and safety information for perlite shows that it will aggravate pre-existing conditions, such as asthma, but does not directly cause lung cancer. Long-term exposure to high levels of this dust can cause a non-cancerous disease called silicosis.
The bottom line: wear goggles and a dust mask. You aren’t in any serious danger but avoid the nuisance anyway. I’ve had perlite in my eyes and mouth, and since then I wear basic protection. Some growers prefer to fill their bags of perlite with water before opening to reduce or even eliminate airborne particulate.
Perlite works great in net cups, and even better in fabric pots. For hydroponics, get the large grade perlite (size #3 or #4). Ebb and flow, dutch buckets, DWC, and drip systems are all excellent methods for growing in perlite. I’ve also seen large plastic totes filled with the stuff, and the gardener watered by hand only when required. To my surprise, those plants were healthy and productive.
If you need reliability, ease of use, ease of re-use, and budget pricing, try growing your next crop in perlite. On a side note, there is a new soil aerator going around that may outdo perlite because it offers many of the same benefits. This new stuff is made in North America from recycled glass so it is truly a renewable resource. It looks like reddish-orange perlite. Be sure to check a local grow store for more details.