I have a Rustica Rubra Magnolia that is about 6 years old. It is in a sun to partial sun location and it is not affected by late frosts. It seems happy, leaves out every year, not diseased, good drainage. I water it in summer and fertilize it once per year, but it still has not bloomed and isn't even growing very much. I don't know what I am doing wrong. What do you suggest? Please help!!