Half my garden struggling

The left side of my garden has been struggling since I planted it about 9 months ago to the point where I thought it was all dead, but there is still signs of life and I want to know what’s wrong. As you can see in the photos the right side which is the same plants have absolutely flourished and are 3x larger than the ones on the left. Any ideas what could be causing this?

The trees are magnolia teddy bears and I wouldn’t be able to tell you what anything else is, just that most of them are meant to be quite hard to kill lol