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, but some agricultural lava products are dust-heavy and need rinsing. The sharp edges that can scrape soft roots also lock plants in place once rooted, which helps tall fruiting crops that would otherwise need staking. A simple vinegar test (no fizzing means no carbonate and an inert rock) confirms suitability.
Crops that work in lava rock
5 edible crops in the catalog list this medium as compatible.
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