Biochar in Raised Beds
Pre-charge, blend through the top 20 cm, and rehydrate the bed — a single application that stays in place season after season.
Last updated April 18, 2026
Why raised beds match biochar
A raised bed is a closed soil system — you control every input. That makes it the easiest place to see what a well-charged biochar amendment does to drainage, aeration, and water-holding. The bed is also deep enough to host the full pore network a biochar application builds into the soil column.
Before you apply
- Charge the biochar. Un-charged biochar can temporarily tie up available nitrogen as it saturates its own pore space. Mix with finished compost 1:1 for at least two weeks, or soak in diluted fish emulsion / kelp for 24 hours. Full methods on the charging guide.
- Moisten the bag. Damp biochar is easier to work with and produces less dust.
Application
- Rate: 10–20 % by volume, blended through the top 20 cm of bed soil.
- Method: Turn the soil with a fork. Spread the charged biochar evenly. Fold it in with the top 20 cm — do not dump a concentrated layer at the bottom.
- Water in: Rehydrate the full profile after blending. Biochar holds moisture well once it is in contact with wet soil.
Coverage from our bags
Math assumes 15 % biochar by volume through the top 20 cm at our measured bulk density of 235 kg/m³. One 6.5 L bag holds 1.5 kg.
| Bed size | Biochar needed | Bags |
|---|---|---|
| 2 ft × 4 ft (0.74 m²) | ~22 L / 5.2 kg | four 6.5 L bags |
| 4 ft × 4 ft (1.49 m²) | ~45 L / 10.5 kg | seven 6.5 L bags |
| 4 ft × 8 ft (2.97 m²) | ~89 L / 21 kg | fourteen bags — worth asking about wholesale |
| 4 ft × 12 ft (4.46 m²) | ~134 L / 31 kg | larger project — see wholesale |
For a non-standard bed, work out the volume yourself: length × width × depth in metres, times your blend rate, gives cubic metres of biochar. Multiply by 1,000 for litres, then divide by 6.5 for bags. Clay beds take the top of the 10–20 % range; sandy beds the middle.
Ontario notes
Southern Ontario raised beds commonly sit on heavy clay subsoil. The top-of-bed amendment works as described, but if your bed drains poorly after heavy rain, a deeper blend — 25 cm rather than 20 cm — plus a tile of gravel beneath the soil column will address the drainage issue directly.