Tuesday, April 6, 2010

The Dirt on Dirt: Texture & Structure

I've been attending a free gardening series held in area during the spring and fall. Yesterday was the first class of the 2010 spring series. It was a presentation on soil by Kathy Rohm. Being a fledgling gardener, I did not know so many things could be said about dirt. The presenter did a fantastic job. Here is some info she shared with us on soil texture and structure.
  • Soil Texture: the size of the particles in the soil
  • Soil Structure: the way the particles are held together
Sand has large, irregularly shaped particles. Because of this, sand has a very loose structure and drains easily, often taking any soil nutrients with the water. It does not hold moisture well.

Silt has smaller particles than sand, but they are also irregularly shaped. It is between sand in clay when dealing with structure.

Clay has very fine, flat particles. It packs very tightly together, holding onto the nutrients better than sand, but not allowing room for air in the soil.

Ideally, most plants prefer the texture found in a sandy loam, which is a mixture of sand, silt and clay. Loam will retain moisture and nutrients so the plants have time to access both. It has a structure which makes it crumbly, allowing air to exist in the soil and plants to spread their roots without being stopped by any barrier.

Kathy suggested a fun test to help determine what type of soil structure you have in your garden. Fill a quart jar 2/3 full of water. Add soil (dried on a newspaper and ground as fine as possible) until the jar is almost full. Screw on the jar lid and shake vigorously.

In 20 seconds, the heaviest particles will settle to the bottom of the jar. This is the amount of sand in the sample. In about another two minutes, the silt layer will have settled. The remaining layer, the clay, can take several weeks to settle. The settled layers can give a fairly accurate estimate of the soil texture in the garden.

Now, where is my Better Half's canning jars?

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