We need to state here the fact that, in mostly any kind of landscape, small trees and shrubs do not require the use of a natural fertilizer upon planting. As a matter of fact, fertilizing at the moment of planting certainly is not recommended. The thing is during the plantation period, the whole energy of the plant is concentrated at the root level.
Fertilizers are not the solution for your soil-related problems. Therefore, the best thing to do is test your soil and see exactly what your soil’s main deficiencies are before you start any kind of fertilizing, regardless of the exact type of plants you intend on growing.
In order to establish your newly-planted small trees, the best practice is that of adequate watering. We could mention here the fact that most shrubs, small trees and plants prefer a soil with a pH ranging somewhere between 5.5 and 7.
At any rate, it can be an excellent idea to go for organic fertilizers and compost, instead of chemical products. You can mulch small trees with shredded leaves, and you can also apply a small layer of compost near the base of your trees. And the best period to fertilize your plants is in the fall, between October and early December.