Hi Jo, 
Shrubs and trees likely don't need fertilizer the way that an annual ornamental bed or vegetable garden do. That said, do you fertilize your lawn? If you fertilize your lawn your trees and shrubs are likely getting sufficient nutrients. Colorado soils tend to be poor (i.e. low in nutrients) so some additional nutrition can be important for good growth, but good watering is even more important than good fertilization.
I think this document from Clemson summarizes nutrient needs of trees and shrubs better than I could: https://hgic.clemson.edu/factsheet/fertilizing-trees-shrubs/ 



I would be happy to chat on the phone to get more specific details from you, just let me know!

Jo, 
It's a little hard to see in your picture, but in some parts of your yard you may be getting some competition from plants because they have become larger. For the Alberta spruce, if there are areas that are dead they can be pruned out, although that will not be as aesthetically pleasing. Unfortunately, once conifers lose a branch they rarely re-grow a comparable one. In terms of the purple leaf sand cherries, you can prune after they have finished blooming, and prune out any dead. If you want to start fresh, you can do what is called a "rejuvenation prune" https://planttalk.colostate.edu/youtube-videos/tree-videos/#shrubs 

I think a phone call or site visit could be helpful. We can offer a Tree Team visit for $25 in which you can look at two trees (and talk in general about tree care) or an overall site visit for $50 where we can discuss the majority of your landscape. Feel free to give me a call at the phone number below or my cell:<personal data hidden>.