GHS Guide to Soil and Soil Testing, Part 2

handful of garden soilSoil is the earth's living skin, as fragile in some ways as human skin. In this second newsletter about soil, we'll tell you what you can do about problem skin, such as if your soil is too sandy or has too much clay. But to do that, you'll need to know what's in your soil, and we'll explain how to perform a free and simple soil composition test.

Soil Composition

Soil composition is the mixture of silt, clay, sand, and organic matter found in your soil. It's important to know what the mix is within your garden because it will affect the type and amount of fertilizer you use, how well your soil drains, how well it holds what you plant in it, and how likely it is to wash away in heavy rains or blow away in high winds. Finally, soil composition indicates how alive your soil isand the more alive it is, the better it is for growing things!

Hollywood should make a movie with people shrunk down to the size of microorganisms and then placed into some rich soil. Viewers would then see that every square inch contains billions of bacteria and fungi, as well as worms, insects, spiders, and other many other critters. The presence of such biological activity is good news: it means that the soil is fully capable of supporting and nurturing whatever plants are placed into it. But this kind of biological activity only occurs if there are good amounts of water, air, and organic material in the soil.

We're not talking about watering hereyou can pour water on a rock for days and no water will get in. We're talking about how porous the soil is, and that depends on the size of the particles that make it up.

Sandy soil allows for water and oxygen to penetrate easily because sand particles are large. However, water drains away too quickly, taking with it any fertilizer you may apply. In this case, the fertilizer you applyand the money you spend on itgoes right down the drain!  On the positive side, it holds plenty of oxygen, plant roots have no problem traveling through it, and it's easy to dig.

Clay soil presents the opposite problem: because clay particles are so small, they make it hard for oxygen to get in, and whatever water gets in will have a hard time getting out, resulting in poor drainage. This type of soil is difficult for plant rootsas well as spades and hoesto penetrate.  But don't despair: this type of soil is generally richer in nutrients than other types of soil, so once you break it up, you won't need to fertilize as much.

Silt predominating in your soil is good news; such soil is ideal for gardening because silt particles are medium sized and usually result in good soil drainage and aeration.  All you have to do is make sure your silty soil contains ample organic matter.

Soil Wash Test

The soil wash is an easy test you can perform that will tell you the approximate proportion of sand, clay, and silt in your soil. Of course, you can pay a lot of money for a laboratory to perform a professional analysis, but for most gardeners this rough-and-ready test will tell you everything you need to know.

mason jar showing different levels of garden soil

Take a glass jar with a tight-fitting lid (a Mason jar will work or any large rounded jar) and put a cup of soil into it. Then fill the jar most of the rest of the way with water. Shake it for 30 seconds and then let it settle. Repeat three times, so the soil is well diluted with water.  Then let the jar sit for three days.

The thickness of the layers indicates the proportions of sand, silt, clay and organic matter. As R.C. Harris explains, With each mixing, more and more coarse particles will drift to the bottom and more and more clay particles will drift to the top, with silt settling out between them. Some of the clay particles may not settle out for several days with this garden soil test: they are so fine they form a colloidal solution in water.

When you take a look at the jar after a few days have passed, you will get a rough idea as to what general type of soil you have, based on whether there's mostly sand at the bottom, clay at the top, or silt floating around. If the results are not clear, Paula Lovegren provides more detailed instructions. Thanks to George Weigel for providing us the mason jar photo!

Improving Your Soil

The short answer is that whether you're dealing with sandy soil or clay soil, the remedy is the same: add compost.  One of our previous newsletters, A Rind Is a Terrible Thing to Waste: The GHS Scoop on Composting, will tell you everything you need to know. And if you don't want to make your own compost, we offer 32 qt. bags of BioMax 3-in-1 Garden Mix, a fine product that combines sea-based compost with black earth and Canadian sphagnum peat moss.

One thing not to do is add sand to clay soil or add clay to sandy soil. It would seem like this would be the easiest solution but due to the varying pH and magnetic charge of the particles, they might end up binding together, causing your soil to be as hard as a rock. Anyway, clay likes to bind to itself, and this alone can cause problems.

If your soil is too high in clay, the best thing to do (in addition to adding organic matter) is to add gypsum to help break it up.  If you have problems with drainage and this doesn't fix them, you might need to dig a trench or take other more extensive actions.

If your soil is compacted because it is high in clay (or for some other reason such as a bulldozer going over it too many times), aeration will help a great deal. This can be done either by renting a machine called a core aerator or by hiring a lawn or landscape company to aerate it for you. For more information, read the Virginia Cooperative Extensions article on Aerating Your Lawn.

If your soil is too sandy, it will need lots of compost. However, compost alone isn't enough; you'll also need to introduce an earth-based matrix. As mentioned, clay isn't a good choice, but peat moss would be ideal.

Finally, keep in mind that improving the composition of your soil will take time. It's something that you have to work at, year after year, but you will see results, even early in the process. The closer your soil gets to being rich and fertile loam, the more productive your garden will be.

Caring for the Good Earth

We hope this newsletter will help you to better care for your soil through understanding its composition. For more information, read Soil Testing Part 1 and Soil Testing Part 3.

Until then, happy gardening from all of us at Garden Harvest Supply!

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