Clay pebbles have been used as a substrate since the early days of hydroponics, and for many good reasons. But as consumer awareness improves, people are paying more attention to where their products are coming from, and while clay pebbles have various excellent properties for their use as a hydroponics substrate, they may not be as eco-friendly as some of the alternatives.
With a variety of choices of growing media available, it’s more than possible to pick a substrate that serves both your plants and the planet.
But what exactly is the issue with clay pebbles, and what makes other hydroponics pebbles a better choice? The answer to that really depends on what your priorities are, and what you consider sustainable. Here’s a look at different substrates and what makes them eco-friendly, or not.
Clay Pebbles
Clay pebbles are small, irregular balls of expanded clay. It’s a mineral product that’s heated to a high degree in the manufacturing process, causing it to harden and expand. This is a versatile and popular growing medium for hydroponics and is valued for its good drainage and reusability.
These hydroponic pebbles don’t have the highest moisture retention but they have a lot of surface area that is great for root binding and cultivating useful microbes in the plants’ root system. The properties of this growing medium make it useful for a variety of plants and as such it’s a common substrate for hydroponics growers.
However, there are some drawbacks. The mining, transportation, and manufacturing process that the clay goes through to produce the expanded pellets is resource and labour-intensive when compared with substrates produced as a by-product of another process, or simply mined and packaged with no manufacturing necessary.
Although it’s possible to mine the clay by relatively low-impact means, the product is quite heavy and only produced in a few locations overseas (namely Germany and China), meaning that both transportation costs, and emissions, go up. Additionally, the process of heating the pebbles to 2000 degrees Fahrenheit emits a significant amount of greenhouse gases.
Because of this, there are viable, more eco-friendly alternatives available. Here is a selection of some of these alternatives and a brief overview of their properties, in no particular order.
Coco Coir
This fibre is a naturally-occurring material retained from the husk of a coconut. It’s a versatile material used in textiles, rope, brushes, and as padding for cushions, but it’s also a very convenient hydroponics substrate.
It has excellent water retention and can be bought cheaply in bulk because of its low weight and compressibility. It drains well and offers good aeration so it’s a versatile substrate for a number of hydroponic plants.
The brown coir processing is very simple, usually done by hand, and results in vast quantities of this cheap, sustainable fibre. It can be harvested from coconuts and processed almost immediately, being combed, separated, and then compressed and packaged. It can be packed into lightweight bricks for efficient packing and transport.
Since it’s a by-product of coconut processing, it’s automatically more economical than a product manufactured specifically for this purpose, however, it’s worth factoring in the country of origin when buying it, as it will likely be traveling halfway across the world, reducing its sustainability.
Coco coir might be a good alternative to clay pebbles, but it’s a very different type of hydro substrate. It will form a matted soil-like bed, rather than the rocky aggregate of expanded clay, so it’s not a one-to-one substitute.
Sphagnum Peat Moss
Peat moss occurs in abundance in many temperate regions of some countries. With modern methods of harvesting, a crop can be replaced naturally over the course of the following year, making it relatively sustainable when harvested within reasonable intensities.
When dried for shipping, it’s very lightweight, meaning lower emissions for transport, and for hydroponics, it’s a fantastic medium for water and nutrient retention. This makes peat moss worthy of consideration as an eco-friendly hydroponics medium.
There are some downsides to this one too, though. Peat moss harvests aren’t always performed sustainably, and peaty landscapes from which to harvest aren’t common worldwide, so again, your order may be flying long distances to reach you.
Practical drawbacks can also be an issue, as the reusability of peat moss isn’t ideal. It will decompose in your system eventually, and this will affect the chemical qualities of the system as well as meaning you have to make another order. Again, this will be a more matted substrate, so not a direct pebble substitute.
Smart Gravel
These recycled pebbles by Arqlite might be the closes to a clay pebble substitute there is. They’re manufactured using 100% recycled plastic from food packaging waste, so unlike other media that are manufactured for the purpose, these help reduce waste and environmental impact.
Smart gravel is made of inert, food grade plastic that have similar root-binding surfaces as clay pebbles and they offer as much, if not more, integrity – creating no dust and not breaking down over time. They are known as, “The Dust Free Alternative to Hydroton,” designed to save hours of prep time and maintain a stable pH. Their strong integrity also makes them much easier to reuse. As far as hydroponics pebbles go, these are a close match to expanded clay, but there are still some significant differences.
Notably, they’re not porous, so aeration and drainage will vary from that of clay pebbles.
As an eco-friendly substitute for clay, this one seems obvious. It’s much lighter, so transport is less resource-intensive, and the source for the materials is addressing a major issue, rather than creating one.
Pumice Stone
Pumice is a naturally-occurring volcanic rock, produced when gassy lava escapes from a volcano. It’s extremely porous and lightweight, and most mining of it involves low-impact processes.
For hydroponics uses, it both absorbs and releases moisture well and can be reused. It’s pH neutral but needs to be washed before use. It can also be reused, due to its longevity. The porous nature of the small rocks makes them good at aerating and drainage for the root mass but they do float in water, so can clog up certain systems.
If you’re familiar with perlite, another common hydroponics medium, you might know what to expect with pumice. However, where perlite produces a lot of dust and involves intensive manufacturing processes, neither of these drawbacks are present with pumice.
Pumice is simply mined, and not manufactured or altered before use, making its journey from the ground to the hydroponics system a relatively easy one. Add to this its low weight, and environmental costs of acquiring pumice are relatively low. It also has good integrity, resisting damage and breakdown, therefore making it reusable for a long time.
Conclusion
For an environmentally- conscious person or business, considering a hydroponics medium is about more than just choosing the right size and properties – it’s about finding a substrate that’s sustainable and eco-friendly. Crops that are sustainably grown can charge higher prices, have greater demand, and are differentiated from a sea of competitors.
Therefore, as we try to move away from destructive mining and manufacturing processes, picking substrates that are a by-product of industry, naturally occurring, or better yet – totally recycled, becomes a priority. It’s the smart choice for both the planet and a business.
