Test peat by squeezing a handful hard: dark, muddy water and a lump that holds its shape mean well-decomposed peat that burns well, while clear water and visible plant fibre mean lightly decomposed peat that burns poorly and smokes. Quality generally improves with depth, from fibrous brown peat in the top 30-50 cm to dense black peat in the deepest layers.
Part of Peat Harvesting
Grading peat by its degree of decomposition using the squeeze test and a dried-block burn, to decide which layers are worth cutting.
Decomposition Sets Fuel Value
The parent article grades peat in three steps:
- Lightly decomposed: fibrous, light brown, with visible plant structure. Low energy, much smoke, hard to burn. Found in the top 30-50 cm.
- Moderately decomposed: dark brown with some fibre. Good fuel and the bulk of most bogs.
- Highly decomposed: black, dense, almost like coal. Best fuel, in the deepest layers.
Soil scientists use a ten-step version of this squeeze test, the von Post scale, which grades from almost-clear water and unaltered plants up to completely decomposed peat that squeezes out through the fingers. The three-step version is enough for fuel.
What You Need
- A spade or auger to reach the layers
- A clean pair of hands (or gloves)
- A scale and a hot, dry place for a block test
- A small notebook to record depth and grade
Method
Step 1: Take a fist-sized handful from the layer you want to judge, at the depth you will cut.
Step 2: Squeeze hard. If mostly clear water runs out, the peat is too fibrous (parent). If dark, muddy water runs out and the peat holds its shape in your hand, it is good fuel.
Step 3: Look and smell. Visible leaves and roots, a springy feel and a light colour mean low decomposition.
Step 4: Test the dried block. Cut one block, dry it for several weeks, then burn it. Well-decomposed peat gives long-lasting glowing coals; fibrous peat flares, smokes and leaves little.
Step 5: Check the ash. Weigh a dried sample, burn it fully, weigh the ash. The parent figure for peat ash is 5-15% by weight. Gritty ash means mineral soil is mixed in.
Step 6: Map the layers. Note the depths at which quality changes and plan your cuts to take the best layer and to set aside the poor surface layer.
Common Mistakes
- Judging a bog by its top 30 cm. It is the worst of the profile.
- Testing with a handful that has dried out. Test freshly cut peat.
- Ignoring mineral content. Sand and clay lower the heat and raise the ash.
Safety
Test pits and cuttings are drowning and collapse hazards
A deep sampling pit in a wet bog fills with water, and a steep pit wall slumps. Keep pits shallow and sloped, mark them, and fill them in. For anything deeper than 1.2 m, the support threshold used in this guide, slope the sides or do not dig (Excavation).
What’s Next
- Learn next: Depth Assessment — how much there is
- Combine with: Cutting & Extraction — taking the good layer