The lone voice of horticultural reason
“Trees and shrubs should be fertilized at time of planting.”
No. University experts I talk to are all pretty much in agreement that it’s best for the plant if you lay off fertilization until the following spring. Research shows that fertilizing at the time the plant goes in the ground can do more harm than good. The roots of the plant are only as big as the container, and while they aren’t dormant, they’re a bit hunkered down and asking hey, what’s the deal here with this plastic prison?
There isn’t enough soil volume in the pot to get them excited and growing robustly, and at time of planting they haven’t grown at all into the surrounding soil. Hitting them with fertilizer, especially of the fast-acting water-soluble variety, can burn the roots.
Container trees and shrubs are all fertilized in their pots with little balls of time-release fertilizer, it’s already activated and they’ve grown accustomed to it. Some of that will wind up in the hole and fill soil, and that’s plenty. In the spring, fertilize the plants you planted the previous year with granular organic fertilizer, and you’re good.
The Renegade Gardener