What does the double-layer box cultivation method for Gastrodia elata mean?

First place a 6 cm thick layer of soybean stalks or sesame stalks (they must be fresh stalks free of mold and rot) in the bottom of the box, level it with growing substrate, plant the first layer of Gastrodia tubers according to the single-layer planting method, and add 3 cm of growing substrate (half of the whole box). Then plant the second layer in the same way as the first layer, and fill with growing substrate until the box is full.