Is the problem using pressure treated lumber,or planting under pine trees?
 

We have built a large planter box under a Monteray Pine tree. We used
pressure treated wood since we only are planting ornamentals, and not
edible plants. We get partial sun and good drainage, but everything
seems to die off after a time. Plants we have tried.Jasmine,
Clemats,Azalias,Coreopsis,Lisianthus, Gardenia. The Hibiscus &
Pelargonium seem to be the only ones still living. What will grow good
under the pine tree? Or is the problem the pressure treated wood???
Charlie