Rockwool (stone wool) is made by melting basalt and chalk and spinning the melt into fine fibres, bound and formed into plugs, starter cubes, blocks and slabs. It is sterile when new, holds no nutrients, and has a very high pore volume, so it can be saturated and still hold a good fraction of air. That makes water content highly controllable, which is why it dominates commercial crop steering.
In practice
New rockwool tends to be alkaline. Pre-soak it in pH-adjusted nutrient solution (about pH 5.5-5.8 is common) before use. Plants start in small plugs, move to 10 cm (4 in) blocks, and finish on slabs. Feed with every irrigation, watch dryback by weight or sensor, and avoid letting it dry right out, as rewetting unevenly creates dry pockets.
Fibres irritate skin and lungs; wear gloves and a dust mask when handling dry material.
Don't confuse with
- Slab: the large rockwool bag a mature plant finishes on; one product format.
- Insulation wool: similar material, different density and binders; not for growing.
The amount of water in a material as a percentage of its weight; cured cannabis flower usually sits around 10-12% w/w, though measurement method matters.pH measures how acidic or alkaline a solution is on a 0–14 scale; in growing it controls nutrient uptake, with soil best near 6.0–7.0 and hydro 5.5–6.5.Dryback is the drop in a substrate's water content between irrigations, usually expressed as a percentage of its content at full saturation.A rockwool slab is a large, plastic-wrapped block of stone wool on which several rockwool blocks sit and finish their roots, the standard format for commercial drain-to-waste.Crop steering adjusts irrigation timing, volume and dryback, along with climate, to push plants towards vegetative growth or generative (flowering) growth.Drain-to-waste fertigation feeds each plant fresh nutrient solution and lets the runoff leave the system rather than returning it to the reservoir.A soilless medium contains no mineral soil, such as peat, coco, rockwool or perlite blends, and relies mostly on the grower to supply nutrients.
