To propose a method of making effective use of virgin tree branches, tree trunks, root stocks, thinnings, drift wood, etc. which are mostly burned or discarded heretofore, as a useful vegetation base material.

Undecomposed vegetable crushed chips 1 are screened or secondarily crushed to selectively obtain vegetable crushed chips 4 each having a size of 50 mm or less, and surface soil containing diatomaceous earth 14, cortex crushed chips of a cedar, a Japanese cypress, etc., or embedded seeds collected near a site is mixed to the chips, and the resultant mixture is conveyed. Then the mixture is further mixed with water, or a polyacrylamide polymer aqueous solution or an olefin polymer aqueous solution 9 to obtain the base material 12 in a form of slurry, which is then sprayed to an objective area, to thereby develop a vegetation foundation.