Question
When planting 3' Thuja trees, can I use 13-7-7 Tree and Shrub fertilizer and should I use Composted Mulch mixed in the backfill or just on top?

Answer
I would not use any fertilizer for the first year. This will give the roots time to grow and not be burned by fertilizer. The mulch should be placed around the tree in a donut shape (keeping it off the tree trunk) not more than 3 inch deep. This is to help hold moisture for the roots.