What is the real concern is being root bound in a 15 gal. container for years. My guess is this conifer is probably severely root bound and major surgery to untangle, clip and free roots would be of majior importance to insure its survival. Did you do this? If not I would probably yank it back out of the ground and resolve this problem

I don't amend the soil. My take on this is the roots will not stay in the amended portion of the soil for even a year so why spend extra money thinking the plant is going to like this. On the other side of the token it doesn't hurt anything if you want to amend the soil...just kind of pointless. My guess is the nursery was only to happy to sell you the mulch and hormone additive. If you have a half of bag left... mulch the planting area...about 2 inches of depth to retain moisture is needed around root crown.

Take care of the roots, water for the first year and you conifer should enjoy a long life.

Best,

Dave

Can you not read.

Otherwise I disagree with you in every respect. Where are your supporting facts about amendments.

Here are mine...hit the link.

Example: If you have an acre of clay and plant your pine in the middle of the acre the roots will reach for the clay and ignore your amended hole in less then a year. Sooner or later it will have to grow in what is naturally available for it