1. Get your soul tested. Most soil is low in nitrogen and acidic.
2. Remove the moss and roots. I have 120 acres north of Willow and cleared 3 acres this June and still had 18 inches of frozen ground under the r-30 moss where as the little bit that I had cleared the year before was dry and ready to work. The cold ground is also why we have low nitrogen in our soil, the soil microbes never get a chance to get working.
3. Choose a garden location that gives as much early season sun as possible.
Soupy soil could be a problem if the spruce and birch are big and health then I would say your ground is solid but if the spruce is stunted you may have a permafrost lens under the soil, walk around and dig down with a post hole digger to get a feel for whats under the surface.
The UA COOP system has a lot of resources for figuring out your soil
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