Types of Soil: Find Yours With Your Hands and a Glass Jar

Types of soil come down to what the dirt is made of. Sand, silt and clay are three sizes of mineral grain, and loam is a mix of the three. Which one you have decides how fast water drains, how much food the soil holds and how easy it is to dig. You can find out at home with your hands and a glass jar.

I am Polarzinho, the studio's panda mascot, and my gardening experience is wiping my paws on the doormat. So I studied. This is the notebook I wish I had, with two home tests to find out what your soil is.

What soil is and how it layers

According to Embrapa, Brazil's agricultural research corporation, soil is a collection of natural bodies made of solid, liquid and gas parts. It starts as rock that rain, wind, temperature, landscape and living things break down over hundreds, thousands and even millions of years, until it is as fine as grains of sand, silt and clay.

Cut into a bank of earth and you see stripes. Each one is a horizon, and the whole stack is the soil profile. From the top, as Embrapa describes them:

1. O: a layer of organic matter, with leaves and roots in decomposition.
2. A: the top mineral layer, darker because it holds more organic matter. It has the most life.
3. E: a layer that lost clay and organic matter, often pale or sandy.
4. B: where the processes that form soil show up best. It is the basis of classification.
5. C: material close to the rock, still resembling it.
6. R: the rock, too hard to cut with a shovel when it is wet.

The types of soil: sand, silt, clay and loam

Texture is the share of three grain sizes. On Embrapa's scale, sand grains run from 2 to 0.05 mm, silt from 0.05 to 0.002 mm, and clay is finer than 0.002 mm.

• Sandy soil: gritty and loose. Water enters fast and sinks away from the roots, and heavy rain can wash part of the fertilizer away.
• Silty soil: silky to the touch. Its small grains make water soak in more slowly, says Embrapa.
• Clay soil: sticky when wet. It holds water and nutrients well, but water enters slowly and can pool.
• Loam: a mix of sand, silt and clay. Clemson University Extension calls it the ideal texture, though most soils are not that balanced and often need organic matter.

Brazilian school books usually add humus-rich soil, dark because of decayed plants and animals, and limy soil, rich in calcium carbonate. To check for the second, drip vinegar on a sample. The Royal Horticultural Society (RHS) in the UK says fizzing means free calcium carbonate is present.

Sand, silt or clay? Telling them apart by hand

Wet a little soil and rub it between your fingers: sand feels gritty, silt silky and clay sticky, as Embrapa puts it. For more precision, use the ball and ribbon tests described by Colorado State University Extension.

1. Knead a handful of soil in your palm, adding water a little at a time, until it feels smooth and putty-like.
2. Squeeze the ball. If it breaks apart with slight pressure, it is sandy. If it holds together but changes shape easily, it is loamy. If it resists breaking, it is clayey.
3. Press the ball between your thumb and fingers into a ribbon and let it hang over your forefinger until its own weight breaks it.
4. Measure the ribbon and rub the soil for grit. Under 1 inch (2.5 cm): sandy if gritty, silty loam if smooth. From 1 to 2 inches: loamy if gritty, clayey if not. Over 2 inches (5 cm): clayey.

The jar test, step by step

The jar test sorts soil into layers so you can see how much sand, silt and clay it holds. This version is from Clemson University's extension service in the United States. You need a clear, straight-sided glass jar, a permanent marker, a ruler, a watch and a sieve.

1. Sift the soil to remove stones, sticks and leaves.
2. Fill the jar about one-third full of soil.
3. Top up with clean water, leaving room at the top. Cap it and shake hard until it forms an even slurry.
4. Set the jar on a level surface. After 1 minute, mark the top of the sand layer at the bottom.
5. After 2 hours, mark the top of the silt.
6. After 48 hours, mark the top of the clay, which settles on top of the silt.
7. Measure each layer and the total height with the ruler.
8. Divide each layer's height by the total and multiply by 100. Those are your percentages of sand, silt and clay.

Plot the percentages on the soil texture triangle. The spot where the lines meet names your soil type, and a balanced mix lands on loam.

Drainage and pH in plain words

Roots need water and air. In very sandy soil, water drains too fast. In very clayey soil it soaks in slowly and can pool. Embrapa says the ideal is a texture that lets water soak in and stay stored without flooding the ground.

The hole test: dig a hole 12 inches (30 cm) deep and fill it with water. Colorado State University Extension says that if water is still there after 24 hours, the soil is waterlogged, which can hurt plant growth.

pH runs from 0 to 14 and tells you whether soil is acid (below 7) or alkaline (above 7). The RHS says pH 6.5 suits a wide range of plants, while lime-hating plants such as blueberries prefer 5.1 to 6.0. Home test kits give a rough reading, and Embrapa points out that pH alone is not enough to decide how much lime or fertilizer to use.

How Brazil names its soils

Every country has its own classification system. Brazil's, the SiBCS, is coordinated by Embrapa Solos, is in its fifth edition and has 13 classes at the top level. Three of them, Latossolos, Argissolos and Neossolos, together cover about 70% of the national territory. Latossolos and Argissolos alone cover about 58%, and Embrapa describes them as deep, highly weathered, acidic and low in natural fertility.

• Latossolos: a latosolic B horizon right under the A.
• Argissolos: a B horizon with more clay than the layer above it.
• Neossolos: barely developed soils with no B horizon.

The other ten are Cambissolos, Chernossolos, Espodossolos, Gleissolos, Luvissolos, Nitossolos, Organossolos, Planossolos, Plintossolos and Vertissolos.

Soil and the clockwork garden of Moss & Bolt

Moss & Bolt, a game from our studio that is still in development, is a cooperative puzzle platformer: a moss creature and a toy robot restore a clockwork garden, and every room needs both. In room 5, the on-screen line says that this time Bolt holds the door and Moss grows the way out for him.

PolarzinhoA little pot with a sprout on the floor of room 5. Soil on a pocket scale, ready to become a lesson.

Look at the small flowerpot next to the robot: it is a flower bed in miniature, and everything in this guide applies to it.

PolarzinhoWaking the garden pump is the easy part. The hard part is where the water goes next: ask the soil.

In room 18, the screen says to use everything you learned to wake the garden pump. Even a clockwork garden needs water. In a real one, the pump is the rain, and the soil decides whether it soaks in, runs off or pools.

How to test the soil in your garden, vegetable bed or pot

1. Look at the color and look for earthworms. Embrapa says dark soil tends to hold good levels of organic matter, and that earthworms are a good sign.
2. For vegetable beds and small plants, take samples 0 to 20 cm deep from several spots, in a zigzag, and mix them in a clean plastic bucket. Avoid waterlogged spots and the area near anthills and fertilizer.
3. Run the ball and ribbon tests, the jar test and the hole test.
4. Measure the pH with a kit and compare it with what your plants prefer.
5. To correct the soil with lime or fertilizer, send a sample to a lab. Embrapa recommends testing at least two to three months before planting.

Common mix-ups about types of soil

• Loam is not a fourth grain size. It is the name for a balanced mix of sand, silt and clay.
• Clay soil is not always soggy. Embrapa notes that some clayey soils have their grains bound into small crumbs, which keeps them porous. Texture is one thing, structure another.
• A pH reading does not say everything. It shows acidity, but not how much lime or fertilizer the soil needs.

FAQ

What are the main types of soil?

By texture, sandy, silty and clay soils, plus loam, a balanced mix of the three. Brazilian school books add humus-rich and limy soils.

What is the best soil for growing plants?

It depends on the plant. Embrapa says every soil has its own best use, and the ideal is a texture that lets water soak in and stay stored without flooding. Clemson points to loam as the ideal texture.

How do I find out my soil type at home?

Rub damp soil between your fingers, run the ball and ribbon tests and then the jar test. To know how much lime or fertilizer to use, you need a lab analysis.

What is the difference between sandy soil and clay soil?

Sandy soil has bigger grains, lets water pass quickly and holds little. Clay soil has tiny grains and holds water and nutrients, but water enters slowly.

What is loam?

A mix of sand, silt and clay, which Clemson University Extension calls the ideal texture.

Your turn

Three samples. The first is gritty and will not even form a ball. The second makes a 6 cm ribbon and feels sticky. The third is dark and full of earthworms. What soil is each one? Answers: sandy, clayey and rich in organic matter.

See Moss & Bolt (still in development)