Can you plant screening amongst mature trees like hardwoods or pines?

Broadleaf evergreens like Chindo viburnum, Ligustrum and Evergreen hollies are more tolerant of being planting in a setting with mature hardwoods and/or pines.  Pines are easier to plant amongst as there is typically less root competition for water and nutrients. Remember that when there is active root competition from mature trees, you will need to provide more supplemental irrigation for the plantings.