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I am starting to get into gardening since I have a bit of garden space for the first time. When I do research online, I often see recommendations for plant soil quality like "rich, porous, somewhat moist soil" for Hydrangeas. I imagine that soil quality varies by region and climate.

How do I determine what soil I have, so that I can optimally choose what plants will grow best in my area?

I live in Swellendam, South Africa, however I am interested in a more general guide rather than details specific to where I live.

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  • Is the type of soil determined by the ph or chemical makeup? All I want to know is how to tell if x plant will grow happily in my garden. – user7520 Dec 8 '14 at 10:03
  • Surely the average noobie gardener doesn't send their soil samples to a lab, right? – user7520 Dec 8 '14 at 10:34
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    @Stacey - the average noobie gardener doesn't. But then the average noobie gardener doesn't seek expert advice on the StackExchange. A soil test will tell you information about soil texture, organic matter content, and nutrient availability. A good lab will even make recommendations about soil amendments based on what you tell them the intended use will be. You're no average noobie ;-) – That Idiot Dec 8 '14 at 13:00
  • What does the average noobie do then? Stick the plant in the ground, water occasionally and see what happens?! Shock, horror! ;-) – user7520 Dec 8 '14 at 13:31
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First, dig down to the subsoil to see what your soil base is. Remove a sample, and spread it out. remove all stones, roots, and debris, and crumble the soil into a fine texture. Fill a quart canning jar (clear) 1/4 full with this soil. Fill it about 3/4 of the way with water, so that there is still some air space. Add 1/2 tbs of dishwasher detergent (don't use regular detergent, as it forms suds when shaken). put a lid on the jar. Shake it very well (at least for 5 minutes - it should feel like overkill). Let it sit for 2-3 days. You should then see layers like this:

Mark the layers as shown in the picture. The clay may take longer to settle completely. Sitting it longer is better if you can.

  • Measure the depth of the sand
  • Measure the depth of the silt
  • Measure the depth of the clay
  • measure the total depth
  • Divide the depth of one of the layers by the depth of the total depth, and you have the percent clay/silt/sand.

Now this works on subsoil because there is no organic matter, which can make this test more complicated. The percentages of particle sizes in the subsoil are the same as those in the topsoil. Here's a chart to find out how to classify this new information you've come up with:

enter image description here

Now for other aspects of the soil, such as pH, om levels, and nutrient profile, you will get best results by sending a sample to a laboratory for analysis. I use my county's extension office. I'm not sure of your local options, you'll have to look around.

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There's one or two simple things you can do without finding a laboratory. We don't go in much for soil testing in the UK (unless it's critical because there's a major problem) so, first and most important, have a look around your area and see what's growing in the ground, and growing well, either in people's gardens or in the wild. I know there's a lavender farm in your region, so the soil where that's growing is probably free draining and fairly light, possibly gritty. The second thing to do is pick up a handful, particularly when its moist - squeeze it and see what happens. If it goes into a solid, sticky ball, there's a high level of clay present; if it remains open and sandy feeling, then it's light and sandy or gritty. If some of it clings together and other parts don't, you may have a high percentage of loam. Dig some over and check whether its full of pebbles or rocks, or even flint or chalk. Dig down a spade's depth and see what the soil looks like at that level, whether it's a different colour and texture. You could also do a ph test, kits are usually available most places, though they're often unreliable, and should only be taken as a very rough guide.

Plants like lavender and other herbs don't appreciate heavy, rich, fertile soil too much, but most plants benefit from a soil that's been enriched with humus rich materials (composted animal manures, garden compost, that sort of thing). These also improve the water retention in light soils, and help to improve very heavy, clay soils.

If you have places that sell plants similar to garden centres or plant nurseries, they may be able to advise you what grows well in your area - once you've discovered plants that do grow well locally, by looking at what soil conditions they like, you'll have more idea what type of soil you've got, though it's not 100% as a guide - water availability makes a huge difference to a plant's growth.

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