When you look at the root system of the plants in question, you’ll find a “soil” mix that grows healthy roots, healthy roots makes healthy plants. You may be surprised that it is real soil from the earth—it's kind of like a potting mix (also called potting soil) made from composted bark, peat moss, and other ingredients that includes earthen soil. If you want your plants to be healthy, try mixing old newspapers in the soil and sprinkle sugar into the mix. Your plants will thank you for it.
-Birdy