Tidal fresh marshes are at least as productive as nearby salt marshes, but much less is known about controls on primary production in tidal fresh vs. salt marshes. We studied a tidal fresh marsh in Georgia, U.S.A., dominated by the C 3 grass Zizaniopsis miliacea . We documented seasonal variation in Z. miliacea above‐ground biomass and below‐ground macro‐organic matter over 1 yr, and annual variation in end‐of‐season abovegrou...