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What is Rockwool?

Rockwool is a type of mineral wool made using volcanic rock. It’s an inert substrate, which doesn’t contain nutrients or microbial life. If you grow using this substrate, you’ll need to use nutrients every time you water this strain.

Benefits of Growing with Rockwool

Rockwool is the ideal substrate for hydroponic cannabis growing thanks to its characteristics; it’s inert, porous, doesn’t degrade, insulating and it holds the roots in place.

One of the downsides, however, is that you can’t grow 100% organically using this method, you’ll only be able to use a few organically-sourced additives.

What Nutrients are Needed for Rockwool?

The perfect fertilizer for this type of substrate is generally mineral fertilizers, as they’re absorbed rapidly.

Most big brands have a range of specific nutrients designed for hydroponic growing such as Nutri Forte A and B, Tripart Grow, Micro and Bloom, or B’Cuzz Hydro Nutrition A and B.

When it comes to growing cannabis with rockwool, your plants’ only source of nutrition is what you give them when watering, so you’ll need to use a soft yet constant feeding schedule.

Prepping Rockwool for Cannabis

Rockwool has a neutral pH level of 7. You’ll need to lower this before you start growing hydroponically.

Cannabis plants grown hydroponically require a pH of:

  • 5.5 during veg.
  • 6.3 during bloom.

In order to reduce the pH levels to 5.5 you’ll need to submerge your rockwool in water with nutrients for a day. The water you submerge your nutrients in should be between 4.5 and 5, and the EC should be at about 0.5 to 0.6.

In order to check if the pH has changed, water using 5.5 pH water and check if the water that drains out of the bottom is of a similar pH level.

Can you Reuse Rockwool?

We don’t recommend using the same rockwool again as it can produce pH related issues. Plus, any organic residues begin to decompose and this type of substrate doesn’t contain any microorganisms capable of decomposing them properly; this can attract pathogens and fungi.

Can you Recycle Rockwool?

Rockwool isn’t biodegradable, although it can be recycled. There are various different recycling systems designed to turn old slabs and rockwool cubes into brand new slabs.

Best Rockwool for Growing Cannabis

Check out our catalogue for varying options:

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