Thank you both so much for your suggestions! I tried to take some photos to show the light conditions now that the leaves are out. This is in the morning, and there's some sun filtering through, but I can tell you there's almost complete shade from the stone wall at the back to about 15-20 ft. in front of the large maple tree all day. From the picture in the next post, you can see there's shade well into the parking lot as well. However, I'm really glad to hear you both think 10 ft. should be sufficient height. Yardvaark, you make a good point about competition from the small maples. So, I think we'll take those out, and possibly the smaller of the hemlocks as well. Then, put in a mix of evergreen and deciduous shade-tolerant shrubs/small trees that reach 10-12 ft with staggered layers for depth. I'm also somewhat relieved you said 'it's not a formal solution'. That means I should just relax since I can't really make a mistake! Lazygardens, I've wondered what the huge rhododendrons people grow around here were - I guess 'rhododendron maximum' is it! Regarding the fence, it's a good idea. I'm not really a fence person, but if we put in smaller, slower growing plants it's going to take a while to screen with greenery, so the fence may be the best short-term solution. Then we can take our time building up the plantings. Yardvaark, I really like your idea of testing out a few small varieties first to see what does well and then increase from there. Cheaper that way, too! Let me know if you have any additional comments/suggestions based on the new pics. Thanks again for your help!

Bamboo is a great choice for containers!! And you do not need to restrict yourself to clumpers - running bamboo is easily contained in large tubs. Boxwood would also work but does grow remarkably slowly and would need to be sheared/trimmed to get the very sharp, clean look you seem to favor. Japanese holly is very similar in appearance and grows somewhat faster so that is a possibility as well, especially the cultivar 'Sky Pencil', which may naturally offer the look you like. Other narrow, columnar needled evergreens with a very restrained habit could work also - Cupressus sempervirens 'Tiny Towers', Cupressus macrocarpa 'Wilma Goldcrest', Juniperus communis 'Compressa', etc. If the phormiums are newly planted, you may very well have some hardiness issues. In the PNW it is not necessarily the cold in winter that knocks them back but rather the combination of cold and our typically winter wet soils. They require excellent drainage and/or a coastal location to really thrive in this area.

You don't have to be afraid of bamboo :-) Many people are uninformed about this plant, have no idea about the many different varieties and that it comes in two forms - running (which can take over the planet and does need a containment system) and clumping. Clumping bamboo does not grow in the same manner as running bamboo and is very well behaved.......the clump just gradually increases in its spread over time like a large ornamental grass does. No travelling vast distances underground and popping up in your neighbor's garden!! Or under your foundation! It has zero invasive tendencies. And clumping bamboos tend to be some of the most cold hardy varieties, with several species rated for zone 5 gardens. They make excellent screening plants with a narrow profile and grow to height rapidly......much faster than a tree or shrub. Unfortunately, the best and most cold hardy varieties would prefer to be sited in more shade in more interior, continental locations, only tolerating a lot of sun here on the west coast. Not sure how well it would work in the OP's garden but it might be worth considering. Cold Hardy Clumping Bamboo The giant timber bamboo Flo referred to, Bambusa oldhamii, is a very popular form of clumping bamboo but it is restricted to warmer climates. But many of the Fargesia species referred to in my link will grow and thrive in cold winter climates, provided they are sited well and given the conditions they need.

"... Goldspire Ginkgo, very columnar variety that is yellow in the fall and should mature to 14' - 16 tall and 5' - 6' wide." Oooh ... I don't think that's gonna happen. It will become much larger. Whenever size information comes from selling sources, it's 100% of the time going to be wrong. And they're stating a size after only a few years of growth, where the tree will not stop. Figure at least double size of whatever you're told. A fat clump of lilac in the tree form sounds like a great solution to the back right bed. You need some groundcover there, too. consider lily of the valley (so long as there's shade.) It does great there. Gotta be some Hosta somewhere, too. And daylilies in the sun. (From DeKalb originally.)