Liquid fertilizers are nice but may be more appropriate for houseplants. Houseplants are harder to maintain in the winter, but they can brighten the home if the gardener has the time and inclination to care for them. Spring is a better time to buy houseplants. It is time now to plant trees and shrubs. Ideally they need to tell you what they want.
Many gardeners have a plan as to how they want their garden to look.
Buying unwanted plants spoils this plan. Ask them what they want or buy them a gift certificate. If you must buy a tree, buy a good one. Some of my personal favorites are Florida or Southern Sugar maple, crape myrtle, red maple, river birch, and several of the oaks. Consider how big the tree will get and what conditions it likes before you buy it.