Hi. I planted about 25 evergreen trees North of Buena Vista (elevation +/- 8,000') in June of 2021. I planted small trees partly because of cost but also because the soil is terrible and about half cobble so really hard to dig. I also wasn't optimistic that all would survive either. They are mostly ponderosa pines and austrian pines (now about 3' - 4' tall) but also three blue spruce (now 2' - 3' tall), two scotch pines (now 5' tall) and two black hills spruce (now 2' tall). I planted them because many of the native pinon trees had died and I wanted some diversification. I have been drip irrigating in the summer and so far all have survived and grown each year. 

My main question is when and how much should I be fertilizing them. So far, at the suggestion of a friend, I have not given them any nitrogen but have given root stimulant supplements. But if feels like it may be time to give them some fertilizer with nitrogen. Given the number of trees and how they're spread out, it would be easiest to use a granular product that could absorb into the soil over time. 

I am also wondering how much I should be watering them. Ideally I'd wean them off irrigation over time. I have been watering once per week, typically.

I appreciate any suggestions. Thanks!