To provide a means for preventing pinetree seedlings and other tree seedlings from withering by salt damage when pinetree seedlings and other tree seedlings are planted on a banking layer or a sandy beach layer of a coast.

When trees are planted on a banking layer laid on a sandy beach of a coast, planting holes are dug at the planting parts of the banking layer, the bottom parts of the planting holes are connected to a sandy area by connection holes and the connection holes are provided with a lower desalination layer packed with a desalination material consisting essentially of a salt removing agent. When trees are planted on a sandy beach layer, the circumferences of the planting holes are provided with a peripheral desalination layer together with the lower desalination layer.