One of the most-asked questions we get about Grodan products is how to recycle stone wool, and whether that’s even possible. After all, many people associate recycling with aluminum, steel, paper products and plastics—not slabs made from basalt rock.

However, this sustainable cannabis growing medium can find a second life after harvest, even in newly legal state markets. In fact, we pride ourselves on helping cultivators find stone wool recycling solutions in various municipalities worldwide.

Grodan’s Application and Development “A&D” division is always advancing innovative solutions for cannabis cultivators to repurpose their used stone wool growing media. The most common secondary application today is a feedstock for the brick manufacturing industry. Additional secondary applications include substrates for green roofs, industrial-scale composting and even agricultural soil reclamation.

These are only a few of the ways that used stone wool is re-applied into new markets. The A&D team continues to explore new applications to make stone wool recycling increasingly easier, cost tenable, and provide Grodan stone wool growers the lowest carbon footprint possible.

Grodan entered 2022 with a 45% worldwide recycling rate—and we’re striving to grow that number. While stone wool recycling is more widespread in some countries than others, one of our goals is to increase awareness amongst licensed commercial cannabis cultivators and assist in building their recycling strategy for opportunities to repurpose their stone wool most effectively in the local marketplace.

Recycling markets vary globally. In Grodan’s work with European agriculture companies, for example, more stone wool is recycled each year than in North America, where the recycling market and agricultural industry operate at different scales. As more cultivators choose stone wool for their grow operations and the legal market expands, however, so will the scale and circularity of the cannabis economy.

“A circular economy” is a common term in logistics and sustainability circles. In a linear economy, any given product moves in a straight line from the extraction of natural resources to use by the consumer to the landfill.

With a circular economy, however, a product either incorporates recycled materials diverted from the landfill or ocean, or is itself recycled into new products, prolonging the lifespan of natural resources and reducing waste. While a fully circular economy is a challenging goal to achieve, any steps business owners can make to curve the linear economy will carry the cannabis industry in the right direction.

Stone wool is considered a sustainable cannabis growing medium not just because of its recyclability, but because of its overall environmental footprint across the product life cycle.

Stone wool is mainly sourced from basalt, a bountiful and naturally renewing, mineral-based material. That certainly gives it an edge over carbon-based substrates such as bog-sourced peat moss or composted wood byproducts found in most potting soils that eventually release carbon back into the environment in the form of carbon dioxide. But stone wool reduces waste in practice because it is designed for data-driven cultivation techniques and Controlled Environment Agriculture (CEA) that reduce water consumption and ease wastewater reuse.

The more stone wool is reused over time, the smaller its footprint becomes. The main limitations of recycling stone wool are the same that apply to alternative cannabis growing media and generalized recycled products as a whole: pricing, location, logistics and regulations are the main drivers for success.

In North America, the distance the used substrate might travel and the array of recycling possibilities depend very much on where a cultivator is based and the recycling infrastructure present in the market. There are typically more cannabis waste operators in well-established legal states or populous provinces, like Ontario and Alberta, than in newer adult-use markets like Michigan and Massachusetts. That said, the patchwork of state regulations also affects the accessibility of cannabis recycling options, and local markets have their own unique challenges.

Some cannabis growing media are more recyclable than others, and each has different levels of carbon impact once you factor the entire product lifecycle. This includes shipping, the efficiencies of the growing process, and potential carbon released through harvest.

From a recycling industry point of view, the problem ultimately facing the cannabis industry has less to do with the recyclability of individual growing media and more to do whether cultivators are taking additional steps to clean and repurpose used product, similar to residential recycling efforts. To support this, the cannabis industry is starting to educate more cultivators about recycling options and the accessibility of sustainability measures available in different markets.