PURPOSE: An agent for preserving plants acting stably and prolongably for a long period even if it is subjected to wind and rain, change of humidity, etc., obtained by adsorbing an organic acid on a carbide.

CONSTITUTION: Charcoal or coal of bamboo processed into a granular state is immersed in a solution of organic acid (properly, acetic acid of wood or acetic acid of bamboo). After adsorption is over, the charcoal or coal of bamboo is separated from precipitated tar components, and the excess solution of organic acid is filtered out, to give and agent for preserving plants. By the application of the agent for preserving plants, the organic acid contained as an active ingredient acts prolongably for a long period, exhibits excellent effect not only on the growth promotion of plants but also on the sterilization and disinfection of culture earth and culture solution, and is useful as an agent for preventing plant blight and an agent for improving and maintaining soil.