Q: I’ve heard that pine needles and oak leaves cause soil to be acid. Is this true?
A: This is a gardening myth that should be put to rest. While needles and leaves from all trees may be acidic initially, they do no acidify the soil as they break down. Soil has a natural ability to buffer changes in pH. Soil acidity might increase slightly for a few weeks after leaves fall but the acidity will go away after a few months. It’s true that pines can grow in poor soil, but they didn’t make the soil poor to begin with. I have research references at bit.ly/mulchacidity