Q.Trees in planters
Experiencing a planning problem over raised decking I have made. Privacy being the biggest issue. Have created a (very expensive) planter, 30 in wide, 38 in deep and 132 in long (over an L shape) and used 32 x 80 liters Sinclair and 12 x 60 liters Bowers g.p. compost to house 6 conifers. As there is plenty “ventilation” through base of raised decking and between wooden frame (there are some 40 air-holes), I believe the trees have better conditions than in the ground.
What I need is a professional to say the trees in this planter have every chance of survival. No one can guarantee this but neighboring similar trees do not have such luxury and are prolific. Unsure who is likely to answer this but would much appreciate comment and contact detail that I may encroach on a little of your time to discuss.

Certified GKH Gardening Expert
I think your setup sounds very reasonable. Really, with any plant in a container, the only real issues you run into are making sure that they get enough water (with proper drainage - and you have drainage), light and that you can fertilize them. Anything can be grown in containers as long as you can get them enough water, light and food.
I would make sure that you choose a plant to grow that can survive one growing zone lower than yours, however. Plants in containers experience weather more like zones one lower because they do not have as much protection from the cold for the roots as plants in the ground.