To plant and grow trees without having the effect of wave erosion due to the gradient of the face of a slope and the fluctuation of a water level while the face of the slope is strengthened by unifying a surface soil layer and a ground layer in the face of the slope on which the fluctuation of the water level is repeated as seen in a flooding lake such as a dam lake.

The rootstock section of a tree 3 and soil are housed in a hollow pipe 1, to which a large number of holes 2, 2... are bored, and the vegetation pile 10 is formed. Pits 21 having approximately the same diameters as the vegetation piles 10 are excavated vertically to the face of a slope 20 on which a water level fluctuates, and the vegetation piles 10 are buried into the pits 21, and the trees 2 are grown.