For the arvorvitae and the box wood I’d go with Espoma’s Tree-Tone. This is a granular food that you’ll place into holes pounded onto the ground (an old broom handle or pipe works well for making the holes) and then fill the holes 3/4 full of the food. The holes should be out away from the trunk or stem about as far as the outermost branch tip (this is called the ‘dripline’). For the flowering plum I’d use Flower-Tone using the same method above. Feed right away and every spring as soon as the soil thaws. This way the plant is getting the food as new growth is forming in spring. Once a year is enough…never feed in the fall.