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Written by davethetreecenters • August 22 Soil Basics for Gardeners

If you are new to gardening, it won’t take long looking at how to grow plants before you meet soil. Perhaps you have already been into your new garden and tried to dig a hole, not really knowing what you were seeing in that ‘pile of dirt’. When you start choosing plants it won’t take long before you meet phrases like ‘needs well-drained soil’, ‘grows best in acid soils’, or ‘grows in clay soil’ – what does all this mean? We have written a lot on this site about the more technical side of soil, but here is a simple, ‘down-to-earth’ piece that gives you the no-frills basics – soil 101 (we won’t insult you and call it ‘Soil for Dummies’.)

Key Things to Know About Your Soil

There are a few basic properties of soil that are the essentials for gardening, and they are what we will focus on. They are:

Let’s take these ideas in turn, and see how to find out what you have.

Soil Texture

Soil is crushed and ground up rock. Natural forces from volcanoes to wind and water turn big rocks into smaller ones, eventually making the tiny particles that make up soil. Since these forces are different wherever you are, every soil is different, but they also have lots in common. Every soil is a mixture of big bits – sand and gravel, medium sized bits called silt, and small bits called clay. It won’t take long before you hear about ‘loam’, and this is the first thing we should clear up. Lots of people think that loam is a thing – something found in soil that is good for plants. It isn’t. Loam means a soil that is very roughly balanced for those three main components. In other words, it is roughly equal parts of sand, silt and clay. So not precise thirds, but round about that. Some loam soils will have more clay, and they are called ‘clay loams’, Some have more sand, and they are ‘sandy loams’. Loam is good because it is the Goldilocks’ porridge of soil – not to thin and dry (as sand is) and not to sticky and wet (as clay is) but ‘just right’.

So how do you know what your soil is?

You could do fancy tests, and send it to a lab, but hey, it’s easier than that. Pick up a small handful of your dirt. (Maybe we should stop calling it that, as dirt is what isinside your vacuum cleaner – soil isn’t dirt.) Pick out any bigger pieces of stone or gravel, and add a few drops of water so you can mix it into a paste the consistency of pastry dough. The mix should stick together, but not be so wet it sticks to your hands. Roll it into a ball and knead it a bit, adding a drop more water if necessary.

Put the ball between your thumb and first finger, and slide your thumb across it to push out a ribbon. Try to make it thin, and about ½ an inch wide. Measure how long you can make it, before it breaks up and falls. If you can only make a ribbon about ½ long, and the soil is crumbly and falls apart, you have a sandy soil. If it holds to about 1 inch long, you have a loam soil. If the ribbon grows to almost 2 inches, you have a silty kind of soil. If it grows more than that you have clay soil. The longer it grows, and the more like Playdough it feels, the more clay you have. You can find more details on doing this test here. You will also notice how the soil feels. If it has a lot of rough particles in it, then it is sandy. If it feels smooth and silky, its probably mostly silt. If it is very smooth and begins to shine when you roll it, that’s clay.

Soil pH

To check this you need some equipment. A visit to your local garden center or big-box store will give you a ‘pH Test Kit’. You can also get simple probes that you push into the soil – very easy to use, but not so accurate. Test Kits use color changes on a chart to tell you the approximate pH. The scale used is simple, but a bit odd. The number 7 is in the middle – neutral soil that is neither acid or alkaline. That’s a good soil to have. Numbers lower than that, like 5.5, 6, or 6.5 are acid. There are lots of plants that will only grow in acid soils, like azaleas, camellias, blueberries or blue hydrangeas. Numbers higher than 7 are alkaline. If you have alkaline soil higher than 7.5 you may find some plants have problems, and the leaves may turn yellow. But other plants, like cherry trees or lilacs, love alkaline soil.

Drainage

How fast water moves through soil is important. Soil is a mixture of those solid bits – sand, etc. – and spaces. Those spaces can contain water or air. Plant roots like them to contain both, since they need not just water, but oxygen to keep the roots alive. Drainage is a measure of how quickly after rain or watering those spaces get air in them.

You can check your drainage easily. Dig a hole about a foot each way, and a foot deep, piling the earth to one side. Choose a spot that hasn’t been dug or tilled for a few months at least. If the soil is very dry, pour in some water and come back tomorrow. If it is reasonably damp looking, you are ready to go. Pour a bucket of water into the hole and start the timer on your phone. How long before the water is gone? If it’s less than 10 minutes you have a very fast-draining soil, which probably tested as being a sandy soil. If it takes between 10 and 30 minutes to empty, that’s great, because you have ‘well-drained soil’, the thing that almost all plants like best. If it takes more than that, and especially if it takes more than an hour to drain, you have poor drainage. If you have poor drainage, or too much, this blog post will give you more useful information. The secret to solving the problems of fast-draining and badly-draining soil is the same. It’s the last thing you need to know about your soil.

Organic Content

Organic material is the result of plants rotting. After a while they lose their original form and can’t be recognized. They become a brown, coarse material called ‘organic matter’. Lots of people think this is ‘loam’, but as we said earlier, it isn’t. You can make your own organic matter by making compost – we have several blog posts on doing that, such as this one. Or you can buy bags of compost at a garden center or big-box store. Or for a larger garden, buy it loose from a local supplier – check for mushroom growers, horse farms or dairy farms. Some landscapers can arrange a delivery for you.

You can tell if you need organic material from your soil texture – if it’s sandy you do, as sandy soils are dry and contain very little goodness for plants. If you have badly draining soil you also need it. Clay soils are rich in nutrients, but if they are always wet roots will just rot. Adding organic matter makes clay soils drain better, turning them into something more like loam. You can get a rough idea of how much organic matte there is in your soil by putting a cup of soil in a big jar, filling it half-way with water, and shaking well. Let it settle for a couple of hours. Are there lots of floating pieces? Is there a layer of loose, coarse, brown material sitting on top of the heavier pieces at the bottom of the jar? If the answer is ‘yes’, you have pretty good soil already, although almost all soils benefit from digging organic materials into them. If the answer is ‘no’, you definitely need to get hold of lots of good-quality material, and start improving your soil. Check this blog post for more details on organic matter.

So Now You Know

Once you have spent half an hour sorting out what kind of soil you have, you are all set to start a garden and make smart choices about what to plant. Ready, set, go!