Lava rock
Also known as: Scoria, Volcanic rock
Properties
| pH effect | neutral / inert |
|---|---|
| Water retention | low |
| Drainage | excellent |
| Oxygen to roots | high |
| Bacterial surface area | very high |
| Reusability | very high (essentially permanent) |
| Cost tier | low |
| Weight | heavy |
How it affects the system
- Best-in-class biofilter substrate: extremely porous, more bacterial surface area per liter than clay pebbles
- Heavy: a 4x8ft media bed of lava rock weighs significantly more than clay pebbles when wet; build the stand accordingly
- Sharp edges: handle with gloves; can damage soft roots of seedlings on initial transplant
- Cheap source for biofilter media if available locally; check vinegar test (no fizzing = inert)
System compatibility
Works well in:
- media bed (ebb and flow)
Avoid in:
- NFT channels
- deep water culture (rafts)
- drip
- wicking bed
Care notes
Source matters: red and black scoria from landscape suppliers is fine; some agricultural lava products are dust-heavy and need rinsing. The sharp edges that damage soft roots also lock plants in place once rooted, useful for tall fruiting crops that would otherwise need staking.
Crops that work in lava rock
5 edible crops in the catalog list this medium as compatible.
Sources
Data drawn from: aquaponics-association, usda-nrcs. Last verified 2026-05-13.
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