PURPOSE: To obtain a solidifying agent, which has good dispersibility and with which a liquid material can be uniformly solidified in a short time without performing strong agitation by blending a powdery highly water absorbing resin and a powdery diatomaceous earth together.

CONSTITUTION: The solidifying agent is obtained by blending a powdery highly water absorbing resin such as a polyacrylic acid based resin and a powdery diatomaceous earth together. The solidifier is added to a liquid material obtained by crushing garbage, etc., and the water in contact with plants to solidify them by the action of the solidifier. Thus the change of properties of the highly water absorbing resin due to the moisture in the air and the sticking of the resin particles to each other are prevented from occurring and the dispersibility of the resin is improved. Accordingly, these liquid materials can uniformly be solidified in a short time while eliminating the need of agitation. Also the solidifying agent is hardly scattered and safely used and further its consumption is easily measured.