I used to believe organic growing meant there's no need to worry about the pH of the soil. While it may be true most of the time, I've learned it isn't always true. There are, of course, many factors involved. Water is one. Nutrients and amendments are on that list, too. A pH between 6.0 and 7.0 is best, with 6.5 being close to optimal. If the pH is too low, excess micronutrients can become toxic. If the pH is too high, macronutrients precipitate out of solution, becoming less available. A pH of 6.5 provides optimal nutrient solubility.
My plants recently taught me about acidic soil. I had to do some research to find potential causes of the plants' symptoms. Eventually, I decided soil acidity was the cause, and I chose amending dolomite lime as the solution. The plants loved it and began growing rapidly. The change was amazing. Up to that point they had been growing slowly, had some red stems, fan leaves were deformed, and leaf tips and edges were necrotic. All those symptoms stopped after I top dressed dolomite lime.
The symptoms had been worsening over several crops. I reuse soil, so that was a clue to the cause of the problem. The soil was slowly becoming more acidic. I am assuming that the main causes were the decomposing organic matter and the use of Epsom salt. According to what I read, acidification occurs while organic matter decomposes and sulfur from the Epsom salt can form sulfuric acid.
Our tap water is consistently a pH of 7.6, so it's not far out of the desired range. It's river water from the mountains, so it's low in dissolved minerals. (Well water is likely to have more minerals due to longer contact time with the Earth.)
