Re: Can we use jello as a fertilizer? If you can, why?

Unflavored gelatin like the Knox brand can be used as a fertilizer. Some boxes 
are even labeled as a fertilizer with a 15-0-0 analysis meaning it contains 15% 
nitrogen. It is not the best fertilizer because it only contains nitrogen, not 
potassium, phosphorus, calcium, magnesium, and other essential mineral 
nutrients. The nitrogen is released slowly as the protein in the gelatin is 
decomposed by microbes.

Flavored gelatins, like Jello, would probably be harmful to plants because of 
the high sugar content, which would reduce water availability.
 
Reference


Knox Gelatin as Fertilizer