Vegetable Garden: Understanding Soil

Day 9 of Garden Tribes’ Boot Camp for novice gardens. Today it’s all about soil–what it is, what it isn’t, and how you make it work for you and your harvest. Before going any further you should know that if you are in a newly constructed house, the “material” surrounding the house may bear little resemblance to soil. Between the time the old house (or whatever) was removed and you moved into the new house, most of the site was probably changed significantly. You may even have the joy of finding MaDonald’s wrappers when you stick a shovel in the ground, or pieces of concrete, or great rocks that had to be either buried or disposed of some other way. So what is said about “soil” here may not actually relate to your situation. I suggest you dig a few good big holes in various not-too-conspicuous places to determine what is down there.

As the expression goes, “Feed the soil, not the plants”.

1. Soil is a complex structure of organic and inorganic things. The quality of soil is dependent on the size of the particles, the amount of air space around the particles, and the percentage of organic matter mixed in among the particles.
   1. Clay is the smallest particle of soil. The more clay, the denser the product, the less air space, the wetter, the heavier it is. But clay is wonderfully full of all the macro- and micro-nutrients and trace minerals needed for most plant growth, and is generally slightly alkaline. More on pH later.
   2. Sandy soil is the opposite: large particles, it holds on to little nutrient, but drains very well. Sandy soil is considered “light”–because it’s not heavy, since it doesn’t hold much water.
   3. Silt is mid-sized particle, easier to work with, but still doesn’t hold many nutrients.
   4. Every ground space has some combination of the above three materials. And once some organic matter is added you have loam–either clay loam, silty loam, or sandy loam.
2. In coastal BC because of our rainy climate, some of the nutrients that contribute to the pH of soil get washed out of the reach of plant roots. So in general we have acidic soil here, which is why rhodos, azaleas, heather, oregon grape, and huckleberry do so well and are found in almost every garden. If you have any of these, and they thrive, you can be fairly confident your pH is acid. That’s not a bad thing (don’t think sulphuric acid here), in that more nutrients are available to plants in an acid environment than in an alkaline environment. So acid is better than alkaline. And if your pH is really low, then you can grow better blueberries than I can!
   • Changing the pH of soil is pretty much a fool’s job. It takes several years of continual application of either a sulphur product (to acidify) or lime product (to alkalinize). Better to just appreciate what you have, and it you want to grow something that prefers a different pH, go with containers/raised beds. This is how many vegetables do well in acidic soil.
3. The key to the good soil that you want to grow your plants in, is organic matter. Material that was once alive, when added to the soil, creates food for all the soil-based organisms that will increase the fertility of the soil. It’s those organisms that take the organic matter (last year’s banana peels and coffee grounds, or the sheep or mushroom manure, or Sea Soil…) and work on it to release the macronutrients (Nitrogen-Phosphorus-Potassium–NPK) and micro-nutrients (Mg, Ca, Fe, etc) that your plants need to grow and fruit.
4. So the last thing you want to do is destroy the community of organisms that are doing the work of providing nutrition to your plants. You want to maintain the soil structure–not too much vigorous tilling, and certainly not every year. You want to avoid synthetic fast release fertilizers which can act almost like antibiotics against your beneficial bugs. And you want to continue to nurture them by giving them a supply of organic material ever year.

Here’s a crappy little video on feeling the quality of soil, and the post that goes with it: the handful of soil sort of sticks together, so it has a little clay, is obviously not that heavy, and not very wet, and doesn’t have much organic matter–it looks pretty grey.