Pine tree sprouts
I have found over thirty tiny pine (or possibly fir or blue spruce) tree sprouts that came up over the winter in my annual flower pots. I have moved them to a separate small pot each. Since most of them sprouted in a pot that was in shade, should their new pots be in the sun/partial sun or remain fully shaded until they get larger? The largest is two inches tall at most. A couple have not shed the seed hull yet. If I can get them through the summer, I will put them in my unheated basement over winter so their roots don't freeze (as the ones I found from last year did that I left outside). Any other tips for helping them grow large enough to plant them in the ground?
Jefferson County Colorado trees and shrubs
Your seedlings are tender and need special care to make sure they don't dry out. They should be kept cool and moist in pots with well-drained potting soil and good drainage. Take care not to overwater. Keep them in a shady spot and avoid windy areas while they are getting started.
Keeping the seedlings from freezing is important, as you said you learned last year. But they will need careful attention indoors for the winter, as they will need bright light not direct sunlight and again careful moisture monitoring.
Once the trees have reached 6-12" they can be transplanted to your landscape.