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100% Coco Expanding Cubes v. Rock Wool

Article by Justin Gilbert & Aron Rosenthal

As many experienced horticulturalists might attest, rock wool can be a highly effective hydroponic medium, touted for its ability to maximize water consumption, reduce fertilizer use, and decrease overall production costs by helping growers increase their yield per square foot of production space. However, these benefits come with profoundly serious environmental and health dangers and we believe it is incumbent upon industry stakeholders to consider the alternatives. 

First, a little about the negative consequences of rock wool. The production of rock wool requires what can only be described as oodles and oodles of energy as raw materials have to be heated to around 3,000 degrees Fahrenheit before they can be spun into fibers and compressed. The production process also presents grave health and environmental dangers to both workers in the factories where it’s produced and also the end users which includes horticulturalists and trade workers. Trade workers mainly use it for home and building insulation and some have even been known to complain of “attic cough” thought to be caused by working with rock wool insulation. If you do use it in your grow facility you should be familiar with, and certainly use, the safety equipment required to work with it. 

However, the most serious consequences are felt by the residents of communities located near rock wool production facilities which perpetually spew toxic fumes 24/7 from unsightly smokestacks contaminating both the community’s air and water resources.


Providing Large-Scale Growers Alternatives to Destructive and Dangerous Horticultural Technology


At Batch 64, one of our main goals is to provide large-scale growers viable alternatives to destructive and dangerous technologies commonly used in horticulture. We share the same objectives as our customers – improve efficiencies, increase yields without sacrificing quality, and reduce our collective environmental footprint. This is precisely why we created and recently launched our compressed coco coir cubes. 

In addition to reducing your environmental footprint, there are other advantages to using coir cubes. For example, our Batch 64 cubes do not require any pre-buffering and only need to be hydrated to fully expand the coir before planting. This can be done by overhead flooding or using a drip system. We recommend a drip system as it’s the most user-friendly “set-it-and-forget-it” setup. It also has the potential to reduce your labor costs when compared to rock wool which has to be buffered with a slightly acidic pH solution (pH 5.5). 

Coir cubes are also more forgiving to growers, especially ones with less experience, because it dries slower than rock wool and helps prevent plants from reaching a permanent wilting point. Another benefit coir cubes offer is a high cation exchange capacity, or CEC. Rock wool, in comparison, has a CEC of zero and can’t hold on to cations (i.e. H⁺, Ca²⁺, Mg²⁺, etc.), which renders rock wool incapable as a medium of making these important elements available to plants and is also at risk of changes in pH. This makes rock wool a highly controllable medium, which is why very experienced growers may prefer it, but it also requires expert management of fertility and pH to guarantee success.

After considering the environmental and personal health concerns, the labor required to constantly monitor your medium’s pH, and other potential pitfalls of growing in rock wool, cannabis industry stakeholders would be well-served to consider the existing alternatives.

Resources: Perry, GA. White Paper: Mineral Wool Insulation is not Green, Sustainable or Environmentally Friendly (June 2019)

Espiritu, Kevin. “Is Rockwool Harmful? Yes, But…” Epic Gardening, 18 Jan. 2019,

Photos courtesy of Next Big Crop

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