I use osmocote or something simular in all of my plants....just make sure its the little bb type slow release fertilizer....If I'm putting it in an already potted plant I just take two fingers and make a hole in the soil add a teaspoon or soo and cover it back up...if your planting new plants I add it to the bottom of a holeless container and then add the soil on top....the only way it would harm the pond is if you just tossed it in--then your water could turn green from all the nutrients--but, putting it in pots you'll have no problems with green water....
Lawanna