Wicking bed soil mix
Also known as: Sub-irrigated bed mix, Coir-compost-perlite blend, Polish bed substrate
Situational use only
Properties
| Bacterial surface area | not applicable (not a packed bed) |
|---|---|
| pH effect | slightly acidic |
| Weight class | medium |
| Longevity | 3 years before degradation |
| Cost tier | moderate |
In a system
- Wicking beds are sub-irrigated: a reservoir layer of LECA or gravel at the bottom holds aquaponics water, and a soil-like growing mix above wicks water up by capillary action
- Typical mix is 50% coir, 30% compost, 20% perlite by volume; the soil layer is 25-30 cm deep with the reservoir 10-15 cm below
- Plants in wicking beds get aquaponics water with the nutrients buffered through soil biology, so heavy feeders like tomatoes and squash perform well even with mild aquaponics K and Ca shortfalls
- The bed itself isn't a biofilter; aquaponics water enters the reservoir without nitrification happening in the growing media. Use wicking as a polishing bed alongside a media bed or MBBR, not as the only grow stage
- Soil mix slumps over 2-3 years and needs to be topped up or replaced; not a permanent installation
Notes
Avoid peat-based mixes; they go anaerobic in the wicking layer. Use coir for the bulk component because it stays open and drainable. Worms thrive in established wicking beds and help maintain structure.
Sources
permaculture-research-institute, milkwood-wicking-bed-guide
See the full aquaponics media reference for comparison, or use the aquaponics system designer to plan a complete setup.