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 water and a soil-like growing mix above draws it up by capillary action
- Typical mix is about 50% coir, 30% compost and 20% perlite by volume, with a soil layer 25-30 cm deep over a 10-15 cm reservoir
- Plants receive aquaponics water with nutrients buffered through soil biology, so in a large enough bed even heavier feeders like tomatoes and squash perform reasonably despite mild aquaponics K and Ca shortfalls
- The bed itself is not a biofilter, since aquaponics water enters the reservoir without nitrification in the growing media; use wicking as a polishing bed alongside a media bed or MBBR rather than the only grow stage
- The soil mix slumps over 2-3 years and needs topping up or replacing, so it is not a permanent installation
Notes
Avoid peat-based mixes, which go anaerobic in the wicking layer; use coir as the bulk component because it stays open and drainable. Worms thrive in established wicking beds and help maintain structure. The whole bed works by capillary action, the same principle as a self-watering sub-irrigated planter, drawing reservoir water up into the root zone.
See the full aquaponics media reference for comparison, or use the aquaponics system designer to plan a complete setup.