The present invention relates to a spreading agent composition for improving the growth of bonsai and landscape trees comprising natural organic matter and rare earth elements for promoting root development, shortening internodes, enhancing hypertrophy of tree trunks, leaf colors, and flower colors in the bonsai and landscaping trees. More particularly, the present invention relates to a spreading agent composition for improving the growth of bonsai and landscape trees, comprising: 20 to 60 parts by weight of natural organic matter; and 1 to 30 parts by weight of rare earth elements, wherein the rare earth elements include 3.0 to 3.95 wt% of neodymium (Nd) and 0.02 to 0.09 wt% of holmium (Ho). Therefore, the spreading agent composition of the present invention not only promotes development of roots at the growing points thereof, but also allows coloration-promoting components of lysine and rare earth elements to shorten the internodes and enhance the hypertrophy of tree trunks and the leaf and flower colors.
