How to read a biochar certificate of analysis
Every bag we sell carries a guaranteed minimum analysis. Here is what each number means, how to interpret it, and which numbers actually matter for garden use.
What is on the bag
Biochar sold in Canada as a soil amendment is exempt from fertilizer registration (it is listed as a primary material under the CFIA Fertilizers Regulations), but the label still has to meet the labelling rules in s.16(1) of the Regulations — in particular, a written active-ingredient declaration. Our label carries:
- Total carbon percentage
- Ash content percentage
- Feedstock declaration (hardwood, untreated)
- Lot number tying the bag to a specific batch
- Net weight in metric, bilingual (English/French)
Each of these is sourced from the supplier certificate of analysis (COA) issued for each lot. We publish more detail than the minimum the Regulations require because transparency on physical specs is part of how we want to sell.
What is on the COA
The certificate itself carries more than ends up on the bag. A full COA typically includes:
- Total carbon (%)
- Ash content (%)
- Moisture (%)
- pH
- Heavy-metal screen (arsenic, cadmium, cobalt, lead, mercury, nickel, selenium) vs. CFIA T-4-93 limits
- Feedstock declaration in writing from the supplier
We publish these full certificates on the Lab Results page, lot by lot.
What each number means
Total carbon
The fraction of the biochar that is stable carbon. Hardwood biochars typically run 70–90 %. Higher is generally better — more scaffolding per kilogram, less mineral ash. Numbers below 60 % suggest either low-temperature pyrolysis (incomplete carbonisation) or a high-ash feedstock.
Ash content
Mineral content left over after combustion. Inverse to carbon in most respects. Hardwood biochars typically fall somewhere in the 1–10 % range depending on pyrolysis temperature and bark content. Crop-residue biochars can reach 20–40 %. Very low ash indicates high-temperature pyrolysis; very high ash indicates either a crop-residue feedstock or incomplete carbonisation — interpret in context with the total carbon figure rather than in isolation.
Moisture
Shipping and storage indicator. High moisture (> 20 %) adds weight you paid for that isn’t biochar. Low moisture (< 5 %) means the biochar is extra-dusty at the open-bag moment. We aim for the 8–15 % range.
pH
Hardwood biochars run alkaline — typically pH 8–10. This matters if your bed is already neutral to alkaline (biochar will nudge it higher slightly), or if you are growing acid-loving plants (biochar is not the amendment for a blueberry bed).
Heavy metals
The CFIA T-4-93 Trade Memorandum sets maximum acceptable concentrations of toxic metals in fertiliser and supplement products. The seven we track:
| Metal | T-4-93 limit (mg/kg) |
|---|---|
| Arsenic | 75 |
| Cadmium | 20 |
| Cobalt | 150 |
| Lead | 500 |
| Mercury | 5 |
| Nickel | 180 |
| Selenium | 14 |
These are the same limits applied to commercial fertilisers and other soil supplements. A pass on the heavy-metal screen means the biochar is acceptable for food-bed use under Canadian regulations.
Feedstock declaration
A written statement from the supplier naming the source of the biomass. Ours: Ontario hardwood, untreated, clean forest biomass. Not treated lumber, not industrial waste, not imported material.
Which numbers matter for the home gardener
In practical order:
- Feedstock. Has the largest effect on how the biochar behaves. Hardwood is our standard.
- Heavy-metal screen. Non-negotiable for food beds. Must be a pass.
- Total carbon %. Higher means more biochar scaffolding per kg purchased.
- pH. Only matters if your bed is already alkaline or you are growing acid-loving plants.
- Ash %. The inverse of carbon; secondary interest.
- Moisture. Shipping efficiency, not soil performance.
Every lot of Charged Earth biochar publishes these numbers on the Lab Results page. If you want the full PDF, it is linked on the batch row.