Soil Texture

Supplies:

2 medium-size stones | 1 piece of blank white paper

Ball of clay or dirt clods from clay soil

small containers (yogurt cups?) of flour, sand, pea gravel, compost, dried leaves, spaghnum moss, bone meal, straw, composted manure, riverbed or pond silt if you can get it

Moist sponge

Glass jar with wide mouth and lid | water

Trowel or spade

           

            The first rule of serious gardening is that you never call dirt "dirt." Real gardeners call it "soil." It's gold to gardeners. The better your soil, the better your garden plants will grow. So we pay a lot of attention to it. So let's learn about our soil before we plant in it.

How many people realize where soil comes from? Have one student start knocking one stone against the other over a piece of white paper. The student should continue doing this as you talk, until everyone can see what is gradually collecting on the paper.

Yes, soil comes from rocks knocking against each other over time, plus "humus" (pronounced "HYOO muss." Humus is organic - once-alive - matter that has decomposed, or broken down, in the soil. Humus can come from plants or animals. Plant parts such as grass, leaves and last year's dead vegetables all form a major part of the humus. Ever wonder why it smells so great in a forest? One of the key reasons is how fertile the soil is after all those pine needles and leaves falling to the ground and decomposing, year after year.

The other part of humus comes from animals - both dead animal bodies, and manure from live ones. After a little while, animal manure doesn't smell bad any more, and mixed with dead plant material and tiny bits of rock, it forms rich, dark, fertile soil.

Soil is made up of three kinds of textures - (1) clay, which is sticky (pass around the ball of clay around), (2) silt, which is soft (pass around the container of flour), and (3) sandy (pass around the container of sand).

You don't want soil that has too much clay in it, because it doesn't drain well, and it is difficult for plant roots, worms, and microorganisms to move through that thick, sticky texture.

But on the other hand, you don't want soft, slippery, silty soil, like you find along a stream bed. Even though silt is nice and fertile, its texture is too soft. A tall plant like corn that is planted in silt won't have the root support underground, and will topple over.

As for sandy textures, while you like to have slightly sandy soil for root crops like carrots to be able to grow straight and true, you don't want too much sand or gravel in your soil because it'll drain moisture away too fast and the plant's roots won't get nourished.

What you're looking for is good garden "loam" - nice, black soil without too much clay in it. It should be "friable" (FRY-able) - crumbly, but not too crumbly - so that if you squeeze a handful of it, it won't clod together, but will slightly crumble when you open your hand again. Squeeze a moist sponge - that's the texture you want.

And you want it to be an "aggregate" (AG gruh get) of all the different ingredients of soil. "Aggregate" means different sized items mixed together. You want a bit of sand next to a larger bit of humus in order to allow for tiny air pockets to let microorganisms move around. Even though it doesn't seem like it, air is a major component of soil, and you want a lot of air in your soil so that plant roots, worms, bugs and microorganisms can do their thing.

Now let's find out what texture the soil in our garden has! Go out to the garden, pick a spot, and dig about six inches under the surface. Bring up enough soil to fill the jar half full. Fill the rest of the jar with water.

Now have a student shake it in all directions for 10 seconds. Set it down, and leave it alone.

Watch the different layers slowly appear. You will see sand and gravel on the bottom, silt in the middle, and clay on top. Then there'll be water, and on the very top, you may have some organic material still decomposing, such as small sticks, moss or bits of leaves.

If your soil forms all one dark layer in the jar, and if it forms clumps and clods in your hand, you probably have clay soil. That's OK: you will just need to add some sand and some compost to make it into a better texture.