Your confusion is completely understandable! You should buy a soil-based potting soil without any added fertilizer. An organic one is best and will have lots of good, organic materials incorporated that will provide the basic nutrition that your aralia needs as well as a good soil texture for proper gas-exchange and drainage.

Stay away from top soil, garden soil, soils with fertilizer pellets or peat-based mixtures. It is better for you to feed your plant with an organic fertilizer every other week during the growing season rather than shock it with a fertilizer-heavy growing medium.

Courtesy of NYBG Plant Information