Vermiculite
Also known as: Expanded mica
Properties
| pH effect | neutral / inert |
|---|---|
| Water retention | very high |
| Drainage | poor |
| Oxygen to roots | low |
| Bacterial surface area | low |
| Reusability | low (1-2 cycles) |
| Cost tier | low |
| Weight | very light |
How it affects the system
- Holds 3-4 times its weight in water: excellent for seed germination and seedling propagation, dangerous for mature plant roots which can drown
- Almost always mixed with perlite for active growing (perlite provides air, vermiculite provides water reserve)
- Compresses heavily over time; one or two crop cycles before replacement
- Has cation-exchange capacity; can mask early Mg/Ca deficiency similar to coco coir
System compatibility
Works well in:
- wicking bed
- soil bed
Avoid in:
- NFT channels
- deep water culture (rafts)
- media bed (ebb and flow)
- drip
Care notes
Primarily used for seed-starting in plug trays, not for the active growing medium of a hydroponics system. Modern vermiculite is asbestos-free; older bulk products (pre-1990s, Libby MT mine) may not be. Buy horticultural-grade from a reputable supplier.
Sources
Data drawn from: cornell-cea, epa-vermiculite-guidance. Last verified 2026-05-13.
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