Hi Keith,
I’m so glad to hear that you regularly water your 3 Spruce trees! The Colorado State University Extension website has a myriad of helpful free online Fact Sheets, PlantTalk and other publications on various gardening topics. Here is the publication about winter drying being a common cause of brown needles (https://extension.colostate.edu/topic-areas/yard-garden/winter-drying-is-a-likely-cause-of-brown-pine-needles/ It explains "Damage typically occurs during late winter to early spring. It is caused by warm, dry winds during times when the tree’s root system is still frozen. Conifers transpire through their needles during winter resulting in some water loss. Periods of warm, dry winds accelerate the water loss, which the frozen roots are unable to replenish. This causes the needles to dry and become discolored. Also, with winter drying, often the bases of the needles and at least some entire needles remain green. In many cases, the damage is minor and, with the exception of loss of some needles, trees recover."

Another great resource is PlantTalk #2123 that explains "Everyone knows that deciduous trees lose their leaves in the fall, but fewer people learn that evergreen trees also lose their old needles sometime in the late summer or fall. Needle age at which drop occurs varies among evergreens and within species.” The article goes on to give some other reasons that pine trees' needles turn brown. Some of these “cultural” reasons include drought, salty soil, root damage, chemical spray damage and soil compaction: https://planttalk.colostate.edu/topics/weeds-cultural-problems/2123-needle-browning-evergreens/
Neither research based article mention the need for feeding Native Trees like your 3 Spruce that naturally grow in our Colorado soils.