Hydrangeas are blue in alkaline (base) soils and pink in acidic soils.

Most fruit trees like acidic soils : Cherry, apple, peach....

Pine trees like acidic soils and release needles that acidify the soil around them. Adding pine needles to acidify soil is not as good as adding the proper chemical but it is safer.

Lime makes soil alkaline (base) but has to be added in very small quantities or it kills plants.