The pH of the soil determines the availability of nutrients. As the soil becomes more alkaline or more acidic, particular nutrients become unavailable to the plants. Whether or not we need to alter the soil’s pH is determined by what we need our soil to do and how effective any treatments are likely to be.
For example, if we have azaleas and gardenias happily growing we’re likely to have an acidic soil because azaleas and gardenias are typically acid loving plants. Therefore, to maintain their health, we wouldn’t want to alkalise the soil. If we did alkalise their soil, they would most likely become sick.
So if our native soil is acidic, we may want to think about what acid loving plants we might plant, rather than altering the soil‘s pH. That’s one option – alter our desires to suit our environment.
If however we want to grow herbs and vegetables and we want an abundance of earth worms and aerobic microbes then an acidic soil won’t typically give our garden or our microbe family a comfortable place to live. For an organic edible garden with heaps of biodiversity in the soil, we generally want a pH of 6.5 to 7.3. That’s a neutral pH.
Because edible plants are generally shallow rooted, altering the top layer of 30cm of soil isn’t too much of a drama. It’s very doable. Therefore, we can easily alkalise the top soil of an otherwise naturally acidic soil and plant a greater diversity of plants.
However if we were thinking of planting deep rooting trees we may find we have a problem because how do we test and then alter the pH way down in the subsoil? Therefore, for planting trees and deep rooting plants, it’s best to choose the plants according to the soils ecology and that includes the pH.
Most healthy compost heaps have a neutral pH. A stinky composts will generally be acidic and be occupied by mostly pathogenic microbes. We wouldn’t want to put the contents of that type of compost on our edible garden.
There are a whole tome of plants that love neutral and slightly alkaline soils. In fact most plants love a mostly neutral soil and that’s where most nutrients are available. However, just as with the acidic soil, the more alkaline the soil becomes the less hospitable to life. So if you have particular plants you want to put in, it’s worth doing some research and finding out their preferred soil pH.
Getting the soil pH in the right spectrum can mean the difference between life and death to your plants and the microbes in the soil. If we’re using our own compost we can test the pH and depending upon its original ingredients and its age, we can be fairly sure it’ll be fairly neutral in pH.
We can also test the pH of purchased composts and soils and I would suggest we do this religiously. Everything we add to the soil changes the chemical composition. Water changes the composition of soil, coffee changes it and so does everything else we may add. Depending upon its pH this can, overtime or immediately devastate the soil and the community of beings living in the soil.
Click here to read about what soil pH actually means.
Click here to read the article to learn more about soil ecology and transforming soil.