Your example is wrong: https://www.thespruce.com/do-pine-needles-acidify-soil-1403128 https://www.thespruce.com/do-pine-needles-acidify-soil-14031...: > When

Your example is wrong: https://www.thespruce.com/do-pine-needles-acidify-soil-1403128 https://www.thespruce.com/do-pine-needles-acidify-soil-14031...: > When a myth dies hard, you can bet that it is either because people want to believe it (for example, when it makes their lives easier) or because there is a kernel of truth in it just big enough to make it convincing. The long-lived gardening myth that pine needles lower soil pH falls into the latter category. It is a twofold myth, erroneously claiming that pine needles should be used as a mulch only around acid-loving plants, and that they will acidify compost if added to a compost bin.... > Perhaps lending further credibility to the myth is that gardeners often observe that it is difficult to grow most plants under large pine trees. They attach an assumption to this observation: It must be that the pine needles shed by the tree cause the soil there to become acidic. However, this is a case of drawing an incorrect conclusion from the facts. The reasons most plants perform poorly when grown under large pine trees are that the trees cast too much shade, or the root system of the trees blankets the soil surface, forming a barrier and sucking up most of the available water and nutrients. A better example would be Black Walnut: https://extension.illinois.edu/blogs/ilriverhort/2018-08-06-plants-inhibit-other-plants https://extension.illinois.edu/blogs/ilriverhort/2018-08-06-...: > Black walnuts (Juglans nigra) are one of the best known allelopathic plants. Black walnut trees naturally contain a chemical called juglone which can inhibit the growth of some plants. Walnut buds, nut hulls, and roots contain the largest amount of juglone. However, even walnut leaves and stems contain a small concentration of juglone.