In general, water is the best fluid with which to water plants. Milk contains a higher concentration of sodium, which would inhibit plants from efficiently taking up nutrients from the soil. Coca-Cola or any other sugary, carbonated beverage contain large quantities of sodium. Additionally, sugared beverages attract insects and encourage rotting.
About this Author
Michelle Z. Donahue lives in Washington, D.C., and has worked there as a journalist since 2001, when she graduated from Vanderbilt University with a B.A. in English. She first covered politics as a reporter for the weekly Fairfax Times newspaper, then for the daily newswire Canadian Economic Press, where she reported from the U.S. Treasury. Donahue is currently a freelance writer.