As with their wild counterparts, bonsai trees have a tolerance of pH within a certain range according to species. If the soil is outside of the bonsai’s pH range, the tree may suffer ill health and lack vigour.
This is a list of tree pH ranges compiled by Marty Klajnowski of San Antonio and originally published in an ABS Newsletter a few years ago; it is fairly comprehensive and a very good indicator of the pH level for individual species.