Thuja occidentalis Care
Dear Extension Experts,
Stark County Ohio
The fact sheet at http://hvp.osu.edu/pocketgardener/source/description/th_talis.html states that it prefers a moist, well-drained, loamy soil in full sun, but tolerates soils that are poor, rocky, clay, compacted, dry, and of various pHs extremely well. So putting your soil mixture around the ball of the plant when planting it should be fine.
As far as fertilization goes, adding some rotted manure or compost to your soil mix should provide an adequate, slow release fertilizer for getting your tree started. In future years, if you take a soil test, follow those resut recommendations or apply a slow release form of a fertilizer with approximately a 4-1-2 ratio of nutrients