To obtain a biodegradable carboxymethylcellulose gel composition for growth of plants, having an excellent water-retaining property and an excellent shape-retaining property, capable of continuously supplying water to cultured plants for a long period, and capable of supplying magnesium and/or calcium as fertilizing ingredients.

This biodegradable carboxymethylcellulose gel composition for growth of plants comprises a carboxymethylcellulose salt, a magnesium metal salt and/or a calcium metal salt, and water. Therein, (1) the etherification degree of the carboxymethylcellulose salt is 0.5-1.6, and (2) the ion equivalent ratio of (magnesium and/or calcium) to the carboxymethylcellulose in the composition is 0.05-1.5. Further, (3) the content of water is 30-99.9 wt.% based on the total amount of the composition.