Unfortunately, most true tidal marshes are flooded with either brackish or saline water which is not conducive to planting/growing plants which would provide food for wood ducks. They are generally too salty. I have had some success planting jap millet in a marshy area that captured rain water primarily but would flood from a wind tide. The millet had already germinated, grew and produced a head prior to the flooding with brackish water. I did heavily lime the marshy area and fertilize it prior to sowing the millet, however. I pesonally think it is a waste of time and effort. If you are not gonna hunt the area, 20 to 30 bushels of corn, placed in the marsh throughout the year, would hold the birds.