Pine needles as mulch are not poisonous.  They make an excellent mulch and are becoming more and more common as a mulch in flower and vegetable gardens and around trees and shrubs.  They stay put in winds and rain, allow water to easily drain through, discourage weed seed germination, and prevent erosion.  As mulch, the needles last about 2 years, and can easily be removed and replaced with fresh needles, or covered with new.  Apply mulch about 3-4 inches thick in fall or spring.  Ideally, it is best if you can work the compost you apply into the soil.

Pine needles have a minimal effect on the pH level of soil.  Utah soils are very alkaline (high pH) and many plants we grow in our gardens could benefit from the addition of any materials that lower the soil pH.