@funcountess Nature is funny - you can't rush it. At the store, your shrubs may have looked nice and healthy from the top, but if the roots were "pruned" to fit the pot or damaged by the way they were handle between field and pot, the have to establish first to get a healthy plant. In that case, too much fertilizer, trying to force top growth over root production, can actually stress the plant and make it less healthy. At most, shrubs should be fertilized twice per year with a general purpose fertilizer. I generally use a time-released one, applied according to directions, around the root zone of the plant. By the way, one of the selling points for Indian Hawthorn is that it is slow-growing, so maybe your neighbors actually plant 2, 3 or 5 gallon shrubs?
Sue