Fertilizer around my koi pond
 

I am new to the site and growing bananas in general. I have some planted around my koi pond in the ground in full south Louisiana sun and a cpl are now flowering. I have only had them planted since Jan of this year and have not done any kind of fertilizing. My issue is the runoff from them can make it into my pond sometimes with heavy rainfall. The pond was not done high enough after it was all said and done. Is there something like those Jobes tree spikes that will work for these? I am thinking that since its in the ground below the surface it may not have much runoff? I am not looking to win prizes or have a ton of naners...im just looking to get good growth and keep them all healthy. Thanks! :bananas_b