How to Identify a Bog in the Field

A six-step protocol — water source, pH strip, indicator plants, peat probe, map overlay, photo record — that ends in a written, photographed observation.

Step one, water source: walk the edge and look for inflows. A bog has none — every drop arrived as rain, which is why it stays acid. Ten minutes of walking settles more arguments than an hour of plant keys.

Step two, pH: dip a strip in an established pool or a hole dug to the water table, never a rain-fresh puddle. A reading of 3.0-4.5 is the bog signature; 6.0-7.5 says rich fen. Allow five minutes.

Step three, plants: a continuous Sphagnum carpet with heather and cotton-grass is the bog cast. Sphagnum holds 15-20 times its dry weight in water, so underfoot the surface should feel like a saturated sponge even in a dry week.

Step four, probe: push a narrow rod to refusal at three points and record each depth. Most northern bogs give 1-3 m; if the rod stops shallow at one point, suspect buried wood and move a few metres rather than trusting the reading.

Steps five and six, map and record: overlay the site on a topographic or soil map to confirm it sits on a rain-fed dome or blanket rather than a discharge zone, then photograph wide and close with the probe for scale. The observation is finished only when all six fields are written down — the comparison table at /bog-vs-fen-vs-swamp and the depth maths at /peat-depth-age-carbon turn those notes into a classification.

• 1. Water source — no inflows means rain-fed
• 2. pH strip — 3.0-4.5 in an established pool
• 3. Indicator plants — Sphagnum, heather, cotton-grass
• 4. Peat probe — three points, expect 1-3 m
• 5. Map overlay — dome or blanket, not a discharge zone
• 6. Photo record — wide, close, and probe for scale

Further reading

• Bog, Fen, Swamp or Marsh?
• Peat Depth, Age and Carbon Numbers