Texture by Feel

The test, step by step

1. Take the sample. A walnut-sized lump from the depth that interests you, usually the root zone rather than the very surface. Pick out stones, gravel and roots.
2. Get the moisture right. The soil should feel like workable garden soil: neither crumbling dry nor smearing wet. Moisten a dry sample drop by drop and knead it through; let a wet one dry a little. Moisture is the most common source of error, so it is worth the time.
3. Look. Can you see individual grains? Visible grains mean sand.
4. Rub. Rub a little between thumb and forefinger, ideally close to your ear. Rough, scratchy and audibly crunching means sand. Soft, velvety and floury means silt. Smeary and greasy means clay.
5. Check the finger lines. Let the soil dry briefly on your fingers. Silt clings in the fine grooves of the fingertips; sand falls off.
6. Roll. Knead the sample and roll it on your palm into a thread about as thick as a pencil. If it will not roll at all, it is mostly sand. If it rolls once but crumbles when you knead it and roll it again, silt dominates. If you can roll it, knead it and roll it again, even thinner than a pencil, the sample is rich in clay.
7. Press a ribbon. Push the moist ball out between thumb and forefinger so that a flat ribbon grows over the edge of your finger, and note how long it gets before it breaks. In the widely used American key, a ribbon shorter than about 2.5 centimetres points to loam, 2.5 to 5 centimetres to clay loam, and more than 5 centimetres to clay. Whether the sample also feels gritty or smooth then separates the sandy from the silty variants.
8. Look for shine. Smear the sample flat with your thumbnail. A glossy surface indicates clay, a dull one silt or loam.
9. Test the stickiness. Press thumb and finger onto the sample and pull them apart. The more it sticks and draws threads, the more clay it contains.

Some soil scientists add one last check: a tiny crumb between the front teeth reveals even fine sand as grit. For a reading in the garden, it is not necessary.

The four main soil types

• Sand: grains visible and tangible, rough, crunches when rubbed, does not cling in the finger lines, cannot be rolled. Water drains through quickly, the soil stores little water and few nutrients, and it warms up early in spring.
• Silt: floury and velvety, clings in the finger lines, dull smear surface, barely sticky, rolls only with difficulty and cracks on the second attempt. Silty soils hold plenty of water in a form roots can use, but their bare surface seals easily under heavy rain and erodes readily.
• Loam: a mixture you can feel at once: some grit, some stickiness, rolls to about pencil thickness, smear surface dull to faintly shiny. Loams combine drainage with storage and are the most forgiving soils for most crops.
• Clay: smeary, sticky and very plastic, rolls again and again into threads thinner than a pencil, shiny smear surface, no grit unless sand is mixed in. When dry it sets hard and cracks. Clay stores a great deal of water and nutrients, but holds part of the water so tightly that roots cannot take it up, and rain soaks in slowly.

Most real soils sit between these types, and their names say so: a sandy loam is a loam with noticeable grit, a loamy sand is a sand that just about holds together.

Three examples from practice

A gritty sample that will not roll. Sand or loamy sand, as it often forms from weathered granite. Rain soaks in readily, but little of it stays. Smaller amounts of water at shorter intervals work better than rare floods, which drain past the roots. Mulch is especially valuable here, because it slows evaporation and, as it breaks down, supplies the organic matter a sandy soil lacks most: every bit of humus raises its capacity to hold water. Deep-rooted, drought-tolerant species cope best.

A floury sample that clings to the finger lines. A silt-rich loam. It holds water well, but bare silt seals into a crust under heavy rain, and then the next rain runs off instead of soaking in. The rule here is never to leave the surface bare: mulch or living ground cover protects it. Water slowly, ideally into small basins, so that nothing runs away.

A sample that rolls thin, shines and sticks. Clay or clay loam. It stays wet for a long time and takes in water slowly. Water rarely, but slowly and thoroughly, and watch for waterlogging in the wet season. A planting hole dug into dense clay and filled with loose soil can collect water like a tub. Mulch keeps the surface from cracking in summer; in winter a coarse, open layer is better than a dense one that keeps the soil soggy. Clay should not be worked or walked on while wet, because that is when it compacts and smears. Species that tolerate wet roots for a while belong here.

The FAO field guide for olive orchards, the classic tree crop of the Mediterranean, rates silt loam as the best texture for olives and pure sand as the poorest, with loamy sand, silty clay and clay not far behind.

Common mistakes

• Wrong moisture. Samples that are too dry are judged too sandy, samples that are too wet too sticky.
• Humus changes the feel. In sandy soil a little humus makes the sample hold together better, so it is judged too loamy. In clay, humus reduces the stickiness. Dark colour also tempts you to overestimate the humus content of sandy soils.
• Lime changes the feel. Clay rich in lime binds less and can pass for silt.
• Only one spot. Texture can change within a few metres, on terraces even from one step to the next. Several samples per area give a more honest picture.
• No comparison. Judging only similar samples blurs the scale. Reference samples of known texture, ideally checked once by a laboratory, keep eye and fingers calibrated.

How Terra Humana uses it

Texture by feel is the first question we put to a soil. It costs nothing, needs no equipment, and within two minutes it tells us how a piece of ground will handle water, which on a dry slope decides almost everything else. It does not replace a laboratory analysis or a spade test; it frames them. Texture is the given, the part of the soil we will not change. What we can change, above all humus and the crumb structure that grows with it, has to be read against it.