Rockwool

Also known as: Mineral wool, Stonewool, Grodan

Properties

pH effect	alkaline until pre-soaked
Water retention	very high
Drainage	moderate
Oxygen to roots	moderate
Bacterial surface area	low
Reusability	single use
Cost tier	low
Weight	very light

How it affects the system

Manufactured pH around 7.0-7.8; must be pre-soaked in pH 5.5 water (mild nutrient solution) for 24 hours before sowing
Sterile by nature: no microbial buffering, so beginner-friendly but unsuited to aquaponics which needs the biology
Compresses over time as roots fill the cube; one-shot transplant medium
Holds excess water near stem base: risk of damping-off in seedlings, root rot in mature plants if oversaturated

System compatibility

Works well in:

NFT channels
deep water culture (rafts)
drip
flood and drain

Avoid in:

media bed (ebb and flow)
wicking bed
soil bed

Care notes

Handle with gloves and a dust mask. Standard commercial-hydroponics starter cube. Most starts from seed begin in a small 1.5-inch rockwool cube, then transplant into a larger system. Not recommended for aquaponics: the biology that defines aquaponics has nothing to colonize on sterile mineral fiber.

Crops that work in rockwool

89 edible crops in the catalog list this medium as compatible.

Sources

Data drawn from: grodan-product-spec, university-of-arizona-ccac. Last verified 2026-05-13.

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