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The Coconut Coir vs. Rock Wool Showdown

Article by Melissa A. Bolin

In the cannabis cultivation industry, growers look for a medium that will provide them with a premium product, but how does a Director of Cultivation make heads or tails of what will efficiently fit into their standard operating procedures (SOPs), be friendly and regenerative to the planet and help produce the most consistently high-yields with the best possible quality? Batch 64 breaks down the good, the bad and the downright ugly in a showdown of coconut coir vs. rock wool.

We’ve All Heard of it, but What Exactly is Coconut Coir?

Coconut coir (coir) is a byproduct of the coconut industry that comes from producing products such as coconut oil and coconut water. The coir fibers are extracted from the husk of the coconut. The fibers are aged, separated, washed, sanitized and at Batch 64, unlike other “clean coco” producers, organically buffered, before then drying and grinding into a fine or coarse growing medium to support your cultivation needs.

The Good: Coir has a naturally occurring ideal pH, excellent drainage, high cation exchange capacity that provides nutrients to the plant as needed, high porosity and aeration, fast dry down times, and excellent habitat for microorganisms in the root zone leading to healthier, higher yielding plants. Most importantly, coir is incredibly easy to use and forgiving – it’s virtually impossible to overwater yet holds onto enough moisture and nutrients that even in the event of a systems failure, commercial cultivators have a much lower risk of a catastrophic crop failure and revenue loss. In addition, coir is 100% renewable, reusable and environmentally friendly. Coir is efficiently used in indoor, outdoor, hydroponic, greenhouse and genetic settings for commercial and medical cannabis cultivation.

The Bad: All of that said, like any medium, coir can potentially have its drawbacks, if the wrong type coir is used or isn’t processed properly. Certain coir can be high in natural salts creating a natural vulnerability to salt build up, can get compacted easily, has the potential to lock out calcium and in some cases, unlike Batch 64, treated with harmful chemicals to buffer. Batch 64 has spent years perfecting our processing methods to ensure these drawbacks are no longer issues when running coir in your facility. 

Rock Wool: Give it to Me Straight.

Rock wool, also referred to as mineral or stone wool, is a man made mineral material that takes a massive amount of energy and processing to produce. The material is used not only in the horticultural industry, but also used as industrial insulation in commercial and residential projects. 


Basaltic rock is melted down at extremely high temperatures (up to 3000ºF) and then spun around in a high powered vat, much like a cotton candy machine, to produce the rock wool fibers that are then cooled down by jets of air. A binder is added, and these fibers are compacted into various sizes of cubes. Cultivators use rock wool in hydroponic growing systems to provide a buffering reservoir of nutrient solution in the root zone while maintaining an adequate volume of air (oxygen) in contact with the roots. 

The Good: Many cultivators use rock wool for its rapid dry down times – allowing for more frequent watering and feedings, high consistency, and cation exchange capacity (CEC) of zero, which means that the nutrients cultivators put into the media is exactly what’s plant available and allows for easy flushing. This makes rock wool highly controllable with the right environment and irrigation systems and controls. Cultivators like its modular nature and the ease of handling. Additionally, rock wool is sterilized during the manufacturing process which many cultivators see as an important benefit. (Recently, however, the product’s sterility has been a large focus of cultivation chatter, as it is still possible for rock wool to host harmful plant pathogens that damage crops and lower yields.)

The Bad: Again, all mediums have their disadvantages, and rock wool can be risky business for you, your grow, your employees and the planet. While highly controllable, it requires a more sophisticated operation and higher levels of staff training to guarantee success over time. Rock wool cultivation requires all systems and controls to be functioning at all times to avoid a catastrophic crop failure and significant revenue loss. Additionally, due to the lack of organic matter in rock wool, beneficial microorganisms, such as bacteria and mycorrhizae, will not thrive as well as they would in coir, which agriculturalists view as critical to supporting not only the plant health, but the entire plant ecosystem. And, unlike coir, you should be extremely cautious when handling rock wool. This man made product can be incredibly irritating to the skin, eyes, and lungs of anyone that comes in contact with the fibers. The United States Environmental Protection Agency lists it as a “Group 2B” product and “potentially carcinogenic to humans”. To reduce your risk of any health complications, always wear a dust mask, goggles, and gloves when handling. 

Two of the biggest stresses and pain points that our customers express is how much additional time it takes to grow in rock wool vs. our cubes. One of our customers recently expressed:

“Batch 64’s cubes have much better root growth than Grodan. I was never impressed by the root zone when growing in Grodan, I hate working with it and it’s inefficient with the labor required. Let me say it again…Rock wool is labor-intensive! 4 employees were dunking the Grodan cubes into the tub then setting them on a rolling tiered shelf. This caused water to drip all over the grow room floor – lacking efficient use of labor and resources. Once 30 cubes were on the shelves, 2 of my guys (one on either side) would roll the shelves over to trays, water is still dripping down from the cubes, onto the shelves and onto the floor. 1 of my guys handed the heavy, wet cubes to another guy who placed them on the tray. Then this process would repeat. It took 6 of my employees 15 minutes for 90 Grodan cubes to be hydrated, put on the shelves and transferred to the trays. That’s 100 hours of labor costs for one task. This works out to be over $80,000 in potential revenue loss due to lack of efficiencies for just this one task. Using Batch 64’s cubes, we’ve cut that time by 75%.” – Head of Cultivation, MPM

Here at Batch 64 we’re into eliminating the non-value added activities for our customers, streamlining your tasks and creating efficiencies. We’ve found that each daily task not completed on the existing manufacturing timeline is a loss in potential productivity. In monetary terms, for your grow, each 24 hours of lost productivity equates to tens of thousands of dollars in potential lost productivity per day. 

The Downright Ugly: Furthermore, the production of rock wool in factories has raised environmental and health concerns here in the United States as citizens are concerned about significant deterioration to the air quality of the areas surrounding the factories. And lastly, there’s no easy way of disposing of rock wool products. Most commercial and home growers just throw it out, destined for the local landfill. There are ways of steaming the wool to potentially sterilize and reuse the product, but the process is highly labor-intensive and incredibly costly. 


Sources: How it’s Made: Rockwool

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