The best way to dispose of common fertilizers is by following the application directions on the packaging. If you can't use the product up, you may have a neighbor or relative that can use it. If that isn't possible, often the only other alternative is to dispose of fertilizer in the trash. This is the least-preferred disposal option, but it may be the only option available in some areas.
Dry fertilizers should be double-bagged in trash bags, then placed in the trash. Small containers (<1gallon) of liquid fertilizer should be wrapped securely in several layers of newspaper, placed in a strong plastic bag or double-bagged in trash bags, then placed in the trash. Liquid fertilizers and pesticides are the only liquid wastes that are allowed to be placed in the trash because it is generally more hazardous to try to stabilize these wastes, especially for chemically sensitive individuals.
These procedures are intended for small quantities of fertilizers from a household only.