10.6 Testing your soil
Four simple tests before you buy soil or plant: what your soil is made of, how it feels, how fast it drains, and what a lab says about pH and nutrients.
At a glance
- Difficulty
- 1 of 4
- Time
- 10 minutes of work, 2 days of waiting
- Tools
- Straight-sided glass jar with lid, ruler, spade or trowel, clean bucket, hose, watch, paper bag for the lab sample
- Parts
-
- 1 Jar test: what it is made of
- 2 Ribbon test: how it feels
- 3 Drainage test: how fast water goes
- 4 Lab test: pH and nutrients
What you need per test area
| Material | Kind | Type | Amount |
|---|---|---|---|
| Glass jar | – | Straight sides, about 1 litre, with a lid | 1 |
| Soil | From root depth | A handful for the ribbon test, enough to fill the jar one third | |
| Water | – | Clean tap water; a bucketful for the drainage hole | |
| Lab sample | 10–20 small cores | Mixed in a clean bucket; about half a litre goes to the lab | 0.5 l |
Why test before you buy?
Sand, silt and clay decide how a soil drains and holds water. Know what you have before you add anything to it.
Most plants want water to drain at 25–75 mm per hour. Much slower and roots drown; much faster and the soil dries out.
pH and nutrients cannot be seen or felt. A lab test tells you whether to add lime, sulphur or fertiliser, and how much.
Simple home kits gave results that differed moderately or highly from lab results in a university comparison. Use a lab for pH and nutrients.
Step by step
-
1
Jar test: shake and wait.
Fill a straight-sided jar one third with soil, top up with water, close it and shake until it is an even slurry. Mark the top of the sand after 1 minute, the silt after 2 hours and the clay when the water clears, after 1–3 days.
Marking the layers on the jar -
2
Read the jar.
Measure each layer and divide by the total height. Mostly sand: drains fast, holds little water. Mostly clay: drains slowly, sticky when wet. A good mix of all three is a loam.
Ruler against the jar -
3
Ribbon test: squeeze it out.
Wet a walnut-sized ball of soil until it feels like putty. Push it out between thumb and finger into a ribbon until it breaks. Under 25 mm: sandy or silty. 25–50 mm: medium. Over 50 mm: clay. Gritty means sand.
Soil ribbon between thumb and finger -
4
Drainage test: fill twice.
Dig a hole at least 300 mm deep and 100–300 mm wide. Fill it with water and let it drain. Fill it again at once, then measure how far the water drops in 15 minutes and multiply by 4 for the rate per hour.
Ruler in the water-filled test hole -
5
Read the drainage.
Under 25 mm per hour: poor drainage. 25–75 mm per hour: right for most plants. Over 100 mm per hour: very free-draining. Do not test when the ground is already soaked.
Drainage rate chart -
6
Lab test: take one mixed sample.
Take 10–20 small cores across the area with a trowel or probe: 50–100 mm deep for lawns, 150–200 mm for beds and vegetables. Mix them in a clean bucket and send about half a litre to a soil lab.
Cores collected in a clean bucket
Specifications
| Test | Reading | Value | Means |
|---|---|---|---|
| Jar | Sand | after 1 min | Coarse grains, settle first. |
| Jar | Silt | after 2 h | Medium grains. |
| Jar | Clay | 1–3 days | When the water clears; Clemson reads it at 48 h. |
| Ribbon | Length | < 25 mm | Sandy if gritty, silty if smooth. |
| Ribbon | Length | 25–50 mm | Medium; loamy. |
| Ribbon | Length | > 50 mm | Clay. |
| Drainage | Rate | < 25 mm/h | Poor. |
| Drainage | Rate | 25–75 mm/h | Good for most plants. |
| Drainage | Rate | > 100 mm/h | Very well drained. 75–100 mm/h is not classed by the source. |
| Lab | Depth | 50–100 mm lawn, 150–200 mm beds | 150–250 mm for tree and shrub areas. |
Grain sizes
The jar separates the soil by grain size, just as a sieve does for gravel (1.1). Sand grains are the largest and sink first; clay particles are so small that they hang in the water for days.
Ribbon flowchart
Universities publish the full texture-by-feel flowchart, which adds grittiness and smoothness to the ribbon length to name all twelve texture classes. The thresholds here are those of Colorado State and Arizona.
Sources
- Clemson University HGIC, Soil texture analysis: the jar test: fill the jar one third with soil, add water, shake to a slurry; mark sand after 1 minute, silt after 2 hours, clay after 48 hours; layer height ÷ total × 100
- Colorado State University Extension, Estimating soil texture: sand after 1 minute, silt after 2 hours, clay when the water clears (typically 1–3 days); ribbon under 25 mm coarse or silty, 25–50 mm medium or fine, over 50 mm clayey
- University of Arizona Extension, Soil texture by feel (2021): flowchart with ribbon thresholds of 1 and 2 in (25 and 50 mm)
- USDA NRCS, Guide to texture by feel: the standard flowchart (after Thien, 1979)
- Iowa State University Extension, Testing and improving soil drainage: hole at least 300 mm deep, 100–300 mm wide; fill, drain, refill, measure 15 minutes × 4; under 25 mm/h poor, 25–75 mm/h desirable, over 100 mm/h very well drained
- University of Illinois Extension, Improving soil drainage (2022): same procedure and rates; do not test when the soil is very wet
- Montana State University, Soil test kits: simple home kits differed moderately or highly from laboratory results
- NC State Extension, Guide to soil sampling for lawns, gardens and landscapes: depth 100 mm for turf, 150–200 mm for vegetable gardens, 150–250 mm for tree and shrub areas; 10–12 cores mixed in a plastic bucket; about 0.5 l sent
- Alabama Cooperative Extension, Home soil testing: taking a sample: lawns 50–75 mm deep from 15–20 spots; gardens to tilling depth; 15–20 cores in one composite sample
- Cornell Cooperative Extension Columbia and Greene Counties, How to take a soil sample: at least 10–15 spots per area, mixed in a clean pail
Inches converted at 1 in = 25.4 mm and rounded.
GLAREUM.NET · Aggregate Handbook