Interactive lesson

Soil testing, step by step

Interactive lesson: split your land into areas, take a proper sample, run home tests of structure, water and soil life, read the lab report and make a plan of work.

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The whole lesson as text

1. Split your land

The lab gives one set of numbers for one sample, so first decide on the areas of your land.

Different use — Vegetable garden, polytunnel, orchard, field, hay meadow and pasture always go in separate samples.
Different soil — Dark soil in the hollow and pale soil on the bank, clay and sand, wet and dry areas: each is a separate sample.
Different history — Where the barn, muck heap, old yard or bonfire site used to be, the sample is separate. A house garden can have ten times more phosphorus than the field.
Size and edges — For a garden or polytunnel one sample per up to 500 m² (about 5,400 sq ft), for a field or meadow per up to 1–2 ha (2.5–5 acres). Don't sample in a 1–2 m strip along tracks, fences and walls.

Why: If you mix an old vegetable plot full of compost and a meadow that has never been fed into one sample, you get an average that is true for neither. One sample is one part of the land used the same way. Garden, orchard and meadow are never mixed.

Draw a sampling map and mark the codes G1, T, O, M. Write the same codes on the bags.
In three years you take samples from the same places and can compare the reports.

2. Take a sample

Half of all testing errors happen before the sample reaches the lab.

Walk a zigzag — Walk across the area in a zigzag and pick 15–25 spots. Five cores, or all of them from one end, give a false result.
Dig a V-shaped hole — At each spot clear the grass and mulch and dig a V-shaped hole with a spade.
Cut a slice — From the side of the hole cut a slice 2–3 cm thick to full depth: 0–30 cm (0–12 in) for garden and field. The slice must be the same thickness from top to bottom.
Mix and label — Crumble and mix all the slices in a clean plastic bucket, put 0.5–1 kg in a bag and label it straight away. If you aren't sending it the same day, air-dry it in the shade.

Why: The sample is a small amount of soil that has to represent the whole area. Autumn after harvest (September–November) is best, and never 2–3 months after liming, manure or fertiliser. Then the report only shows what you have just added.

Don't use a galvanised bucket or a brass trowel if you are testing for trace elements or heavy metals.
Never put a sample in an old fertiliser or lime bag.