Soil Biology Assessment — Jar Test
A simple jar settling test that reveals your soil texture (proportions of sand, silt, and clay) and organic matter content. Takes 24-48 hours and requires no special equipment. Results guide amendment and planting decisions.
Version History
Version 1.0 Current
Effective: 2026-03-27Initial version
Procedure Details
No hazards. Wash hands after handling soil.
You will need:
- Clear glass jar with lid (1 litre / quart size works well)
- Soil sample from 10-15cm depth (composite from 5+ spots in the bed)
- Water
- 1 teaspoon of dishwashing liquid (helps soil particles separate)
- Ruler
- Permanent marker
- Timer or clock
Procedure Steps (Version 1.0)
Collect a composite soil sample: take 5-10 small scoops from across the bed at 10-15cm depth. Mix together and remove any rocks, roots, or debris.
Fill the jar one-third full with soil. Add 1 teaspoon of dishwashing liquid.
Fill the rest of the jar with water, leaving 2cm of air at the top. Screw the lid on tightly.
Shake the jar vigorously for 2-3 minutes until all soil is fully suspended in the water.
Set the jar on a level surface and do not disturb it. Start timing.
After 1 minute: mark the top of the settled layer on the jar with a permanent marker. This is your SAND layer (the heaviest particles settle first).
After 2 hours: mark the new top of the settled layer. The material between the 1-minute mark and the 2-hour mark is your SILT layer.
After 24-48 hours: mark the final settled layer. The material above the silt line is your CLAY layer. Any material floating on top is organic matter.
Measure each layer with a ruler. Calculate percentages: each layer height ÷ total settled height × 100.
Record the date, bed/zone tested, and measurements. Compare to a soil texture triangle to determine your soil type (sandy loam, clay loam, silty clay, etc.).
Use results to guide amendments: high clay → add gypsum + compost for drainage; high sand → add compost + clay for water retention; low organic → add compost and mulch.