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Soil Composition 101 — Dirt


Okay, so this is not a college level course on soil composition but it is brief and steady jog through the key points of dirt prep and balance.  Based upon the balance between your soil’s main ingredients, we can determine a great deal about its growing potential.  So what if you failed organic chemistry many moons ago and don’t know pH from polymers?  No problem.

First, soil is made up of clay, sand, silt, and some biological sediment.  I didn’t make up the rules, that’s just what they are, okay?

Sand is that largest particle in the soil and is irregular in shape. The sand particles do not fit together snugly, so there are gaps between the individual particles. The gaps provide a space for air and water to collect which is needed by the plant roots. The gaps also mean that the sand can be easily accessed by roots. Too much sand will allow water to drain quickly from the surface and plant roots become deprived of nutrients and water.  Basically, the plants wither and die of dehydration and are then washed away completely when the rains come.  Why doesn’t CSI do an episode on that?
Silt is the middle size particle and perhaps the ideal for a garden. The size of silt particles allow it to retain moisture, as well as allow ample root growth, but also have enough cohesive energy to retain nutrients well.  This is like gummy Flintstones vitamins for kids — good for them and utterly fantastic.
red soil

Clay is the smallest size particle and most of us know clay better than any other form of ‘soil’.  Clay and I became well-acquainted when we moved to Western Georgia and we couldn’t till a garden and were forced to build raised beds. These stubborn soil particles are small enough that they fit tighter closely and form a layer.  Multiple layers fit snugly together in a way that prevents water and nutrients from penetrating. The result is that roots cannot penetrate the clay and drainage is poor. Basically, the plant dies a miserable death. On the positive side, clay isn’t necessarily all bad. It has good moisture and nutrition retention. But that same “good” moisture retention can also be a problem, as I already pointed out.
soil triangle
Most of us have a mix of all three particle sizes plus some organic material.  Unless, of course, you are one of my neighbors and then you have only one particle size.  If you look at the triangle above with silt, sand and clay at the corners, the central areas are the best soil composition. Most natural soils are on the lower part.  This means that all you have to do is add a little bit of one component to balance your soil and create a productive garden space.  You lucky things, you.  I burn with envy.
soil jar
Now that we’ve talked about soil, I’m sure that you are just itching to figure out what you’ve got in your backyard — your hidden garden potential.  Okay, maybe you’re not.  Maybe you already know and you’re reading this because you are just really loyal (if so, I really love you).
soil jar2

Whatever your reasons — take a shovel and dig a hole about six inches deep and remove the surface layer. Spoon about one cup of mix into a glass canning jar (or any clear container) and fill with 2 cups of water.  Shake it up for several minutes to fully mix the contents and yell, “Yahtzee” really loudly.  Let the jar sit for 24 hours and take a peek.  The small clay particles will be on the top, the coarse sand particles are at the bottom.

Now you know what you need to do to improve your soil.  Repeat the soil composition test in different areas of the garden and yard, then log it carefully in your garden journal or a random notebook that your kids have abandoned for no apparent reason.  This log will help when you attempt to plant in those areas and must know what to add to your soil to make it work for your needs.

This is the first of many soil themed posts.  I’m planning more.  MORE dirt!  Tune in next time for chats on green manure.  Check out other totally awesome and informative posts by visitng The Very Best of Our Site.  Or not.  But I really hope you do.

  • Michele - This is important information about dirt. I glad you took up the spade to handle it. It’s a dirty job but someone had to do it. OK, I’m sorry. Enough puns.

    I love, love, love the beach picture. Would you mind if I painted it for my own collection? I promise to send you a copy if you want one.ReplyCancel

  • Rosa - I love that red soil! It makes me think of australia…



  • Kelly - Our soil is an experiment in variety. Within a 10 sq meter dig, you’ll find straight sand, rock hard compacted clay, fertile humus, and plain ole rocky dust. Today we’re slathering nearly the whole property in chicken poo. Fun!

    BTW, your comments box isn’t working very well in Internet Explorer. Some kind of javascript error. I had to use Firefox to get it to work. Might wanna have a look at your ad code ’cause it seems to be plowing over the comment box.ReplyCancel

  • warren - Very interesting! Have you ever had anyone analyze the chemical content of you soil? We always have the extension agent check for ph, nitrogen, etc. I am curious what else may lurk in there…ReplyCancel

  • shelli - I know all about clay soil. My entire yard was pretty much hardpan when I moved in. The grass sort of grows, but it does struggle. One day I’ll till the whole thing up and put a layer of nice topsoil in. I fixed my garden beds by adding lots of organic material, some sand and topsoil. Each year I add more compost and turn in my mulch from the previous year. By the time I move out of here, I’ll have nice soil to leave for the next gardener.ReplyCancel

  • gingela5 - Good old red dirt–nothing better! That’s all we have in Oklahoma!ReplyCancel

  • CC - I think what I really need to do if have you come visit and HELP!!!ReplyCancel

  • Nivenheim - Just wondering if anyone knows a good source of infomation which has an element composition list of common soil types? As in if its iron rich or has very low sodium.

    More of just a scientific breakdown rather than how well something will grow in it.

    Thanks for your time.ReplyCancel

  • renee - If you like this check out Dirt! The MovieReplyCancel

  • A Tour » Razor Family Farms - […] contains everything you ever wanted to know about soil composition, DIY organic bug sprays, the benefits of eating purple vegetables, and composting.  It’s the […]ReplyCancel

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