When it come to wild ducks it's best not to feed them at all. People feed the ducks all the time at the frog pond and some ducks will eat right from people hands. This is not good for the ducks as they're becoming too tame and depending on people for food. I tired telling people bread is bad for ducks but most people do not believe me. I would be careful feeding ducks too much veggie and could give them the runs .They can eat a little iceberg lettuce at a time too much iceberg lettuce is no good as it has no food value . I know ducks loves to eat snails, I worked on a farm and we take big cardboard boxes and cut them up and leave it on the ground over night .
In the morning there would snails under the cardboard and we let the ducks have a party. It was a great way to get rid of the snails as they could wipe out a lot plants over night.