You could try feeding them a bit now and then or grow your plants in a floating ring w/fiberglass door screen attached to the bottom. W/o a camera underwater it will be hard to know if they are eating them or not.
I have used a floating ring like this one and you can make them any size you like. I sewed mine together w/fishing line. You might want to use larger tubing than I did as some of the fish jumped right into the ring
and then of course could not figure out how to get back out. I got the fiberglass screen door material at a hardware store. Cut a strip for the sides, sewed that on ring and then sewed the bottom circle onto the sides. Used a plastic connector thing to attach the tube ends together that I had laying around. You can buy them at the hardware store also and they need to fit tight to allow no water into the tubing. One thing to keep in mind tho if any fish eggs hatch near this thing the fry are so tiny that they can get in there and survive and other fish can't get them.............well except if any bigger ones jump in there. Still a lot of babies and just a few jumpers will allow many to survive. There are other ways to keep fish away from your plant roots. You can hang bags on the sides of the pond w/this same kind of material so just the roots are in the bag and the plant tops float out but w/lots of floaters you might have to make some kind of a long tray or whatever, just anything to keep the roots safe from those piggy fish! Still this is all a guess if the fish are eating them or there is some other issue that I can't tell you.