Duck feeding advice?

[new2ducks]

my 2 ducks have cut back on eating weeds...they were wild about them at first and I was so excited about them eating the weeds, so I just let them grow on the one side outside of their kennel, now I have weeds galor over there and have to pull a few every morning to thin them out and I saw a very small garter snake(first time seeing a snake!!!!) so I bakced off pulling for a little bit. I give them food and tried to throw it out by the weeds so they would eat there and they just leave it alone so the flies and the other birds get it. Any ideas?