Can I Have Soil Up The Stem Of A Tree

Question

I have 2 young kowhai trees in my garden. I am having a planter box build around them (about 20 inches deep). Do I need to transplant the trees or can I just fill in the planter box with them staying in place.

Answer 1

No, you wouldn't want to add soil to the stem of the tree, it would invite stem rot.
Can I talk you out of building planter boxes around the trees? It could ultimately cause the demise of the tree due to suffocating roots. It's best not to add anything on top of tree roots other than mulch out to the dripline.

https://www.gardeningknowhow.com/ornamental/trees/tgen/planting-garden-beneath-trees.htm