Quick question for you Attila Soos, I was curious to how well these blue spruce are doing down in your area? I was looking at the hardiness zones for this tree and they are 2-7 and I am at about 8.
I would imagine its a little hotter down there in the winter and was kind of concerned about my zone but if your trees are doing well then I hope mine will too.
Do you do anything special for your trees besides water and fertilize?
I have a few Sitka spruce, Chihuahua spruce, Quinghai spruce, Dwarf Alberta spruce, and a few others (P. koyamai, P. retroflexa). These are the only ones that can survive the So. California climate. The Sitkas are actually doing great. One of them is a little collected tree that I've been growing for 15 years here in L.A. I don't have colorado blue spruce, that wouldn't survive down here. To me, these are not serious bonsai subjects, rather just toys to satisfy my curiosity towards the species. I don't expect them to become show-worthy bonsai, ever. For that, you need collected specimens.
I used shade cloth the last few years, but this year I decided to take it off, since I have a large oak tree that provides afternoon shade. The bigger problem is the mild winter, these trees need the winter chill, a certain number of cold days, in order to survive.
I think your climate may be still ok for the blue spruce, not ideal, but borderline. As long as you don't expose them to the scorching heat (needs afternoon protection), they may have a chance. Spruce needs a lot of sun though, so it can't be too much shade. California has a lot of micro-climates, so you have to experiment in your particular area.
The problem with trying to grow trees out of their ideal zone, is that even if they survive, they don't give you too much room for mistakes. They give up easily, when they are abused. That makes this a risky affair: you can invest many years working on them, and then you make a mistake and they die. This is what happened with my redwoods, down here. I spent a lot of money on them, and then lost them. But after a few failures, I think I finally learned how to grow the coast redwood in L.A.