The best cannabis substrate: Coco vs Rockwool

The strengths and weaknesses of coco coir

Coco coir is an organic substrate made from coconut husk, with a naturally porous structure known for allowing effective air and water exchange. Growers who use crop steering techniques may prefer coir thanks to its higher cation exchange capacity, which enables it to better supply nutrients and makes it less susceptible to quick changes in electrical conductivity within the root zone. It’s also typically more forgiving, as plants growing in coir will start to demonstrate physical stress responses before the amount of available water gets too low.

Coco coir is often packaged in compressed blocks, making it easy to transport and store on-site –  but because it’s produced primarily overseas, shipping can increase coir’s impact on the environment.

As a natural substrate, it’s minimally processed and can be recycled for soil mixing, home gardens, and other outdoor uses.

How does Rockwool compare?

An evergreen favorite in hydroponic growing, Rockwool is a substrate made from basaltic rock that’s been melted down and spun cotton candy-style into fibers, then shaped into grow cubes or slabs.

Growers appreciate Rockwool’s ability to retain water – its matric potential curve is more linear than coco’s, which means Rockwool can achieve nearly 0% water content before plant stress becomes visible. In this way, Rockwool is less forgiving than coir – so it’s a good strategy to adopt Rockwool after your facility’s irrigation and environmental parameters are dialed in.

As a processed product, it’s more taxing on the environment than coir is, but some individual manufacturers may provide recycling options.

Rockwool is also often shipped on pallets, which can lead to damage and impact its effectiveness as a cannabis substrate.

Let target outcomes lead the way

At the end of the day, choosing between coco coir or Rockwool ultimately comes down to what works best for your business needs as a whole – not just the plants. Choose wisely.

For more on the debate between coco versus Rockwool, check out this segment from Office Hours episode 49.