The University of Minnesota, et.al., teach that pine needles are acid
but that is totally hogwash, balderdash, horse feathers. etc. Pine needles
are no more acidic that most other mulches.
Before I began testing the pH of pine needles, I had purchased some
lingonberry plants. The sales person instructed me to plant them under a
pine tree adding that the ground would be acidic. When the plants died, I
had the soil tested and the lab found it to be slightly alkaline! When I
acidified the soil for planting more lingonberries, the pine tree died.
In a Horticulture class I teach. I advise students to mulch with pine
needles because most rain water passes through whereas most other mulches
need to be thoroughly moistened before the soil gets wet. Another major
advantage of pine needle mulch is that it takes up to five years for them to
breakdown.