I collect and use rain water for my bonsai as much as possible but 70% of the time I have to water with our pH 8-9 alkaline city water when I run out of rain water.
Plant roots have difficulties absorbing iron, zinc and magnesium micro-nutrients in alkaline soil. These micro-nutrient deficiencies caused leaf chlorosis especially in azalea and gardenia. When that happened I foliar sprayed my plants with Epsom salt or chelated iron acidifier. They worked well in treating the symptom but did little or nothing to improve soil acidity. Most plants grow best when the soil is slightly acidic. I usually sprinkle a little sulfur powder to my soil and let the microbes convert it into sulfuric acid to lower the soil pH. But this is a very slow process. Some people add vinegar to lower the water pH during watering.
Recently I started doing Bokashi composting with…
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