Calcium silicate hydrate is proposed as a potential silicate fertilizer. It is the main phase of the by-product of a mild hydrochemical process used to extract alumina from coal fly ash. Its preparation by decomposing sodium calcium silicate hydrate, the residue after extracting alumina from coal fly ash, was investigated. The results revealed that the intermediate of the sodium calcium silicate hydrate was easily decomposed into calcium silicate hydrate in a dilute alkaline solution and an available silica content of 28.57% was obtained under the decomposition conditions of a 30 g/L Na2O solution, a liquid-volume to solid-mass ratio of 25, a reaction temperature of 150 °C and a reaction time of 4 h, with a stirring speed of 600 rpm. Subsequently, Si uptake experiments were conducted on wheat seedlings by hydroponics to test Si’s effects on their growth. The results proved that the Si concentration in the wheat seedling shoots was greatly enhanced from 1.213 mg/g to 3.983 mg/g when 0.02 g of calcium silicate hydrate was distributed in the pot in which 3.87 g of seeds were cultivated.