Hello Gardening Forum,
I'm fairly new to home ownership and brand new to gardening. I live in Los Angeles, about 3 miles from the ocean, in a residential neighborhood. In an effort to privatize my backyard from the neighboring alley, I had some contractors build a planter trough in place of a rotting lattice fence on top of a 4-foot high brick wall. We were somewhat limited by the width and beginning height of the brick wall, but I was assured by a local garden store that I would be able to grow Japanese Boxwood into a formidable hedge over the course of a few years with what we had built.
I'm attaching pictures and will explain how they were arranged ...
Each plant is separated by 2.5 feet and has approximately 1 foot of soil depth. They were all purchased in 1 gallon nursery pots, so the existing root systems actually have a good 5-7 inches of potting soil beneath them. The trough is connected throughout its lower half, without interruption, so the roots of each plant can grow as far left and right as they please, until, of course, they run into those of their neighboring plants. The wood is treated to protect against termites, rot, and fungus. We also lined the inner walls of the trough with thick #30 roofing paper, which essentially guides water to drilled drainage holes on the bottom of the trough. These dump into the alley and seem to work quite well, as they typically begin evacuating water after about 20-30 seconds of watering the plants.
My concern here is that I can't seem to find any existing evidence of someone else trying to cultivate a boxwood hedge with this little depth. They're starting to grow a little after only about 3 weeks in the planters, but I still have some specific questions ...
1. Is 12 inches enough depth to get one continuous hedge reaching 3 feet in height? If not, how high should I expect them to grow?
2. Are the plants too far apart (2.5 feet), in light of the planter depth? *If so, I can easily reduce the separation and add more, as the roots have not yet begun to 'take hold' in the soil.
3. How should I be pruning these if my goal is to get them as wide and tall as possible?
4. How should I be pruning these if I wish to prioritize width over height, in the short term?
5. Am I insane to think that because each plant has plenty of space for its roots to grow laterally, that the hedge itself might mimic this root growth? In other words, will the plants grow less in the directions of the alley and interior of the yard, and more side-to-side, in the directions of their neighboring plants, because of the shape of their container?
6. I know that Boxwood are known for being slow, low-maintenance growers that can be pruned into just about any shape. However, if one were to wish to make them slightly faster growers, how would one go about this?
Those are my biggest concerns for now. Would love to get any and all advice, as well as any pictures if you've seen someone else try this before! Thanks!