To provide a paste agent for a culturing soil for growing seedlings, capable of maintaining a good solidifying state stably without being affected directly by the property of a base material of the culturing soil for growing the seedlings and also excellent in sowing work efficiency and preserving property, and a culturing soil for growing the seedling using the same agent.

This paste agent for the culturing soil for growing the seedlings consists of a starch and a copolymer obtained by polymerizing monomer components containing a monomer having addition polymerizable double bond. As the above monomer having the addition polymerizable double bond, a (meth) acrylic acid (salt) is suitable. The culturing soil for growing the seedlings is obtained by mixing the above paste agent and the base material for the culturing soil for growing the seedlings.