This is an old gardening myth that just won’t rot away!
This common, incorrect, advice goes as follows: if your soil is alkaline (ie has a pH above 7) and you want to make it more acidic, add pine needles to the soil. Since pine needles are acidic they will acidify your soil. This advice is very prevalent especially for growing acid loving plants such as azaleas and rhododendrons.
There are two important questions to ask. Firstly, are pine needles acidic? Secondly, do they acidify the soil? Let’s have a closer look at both questions.