Growing halophytes floating at sea

•Halophytes grew for 733days floating potted at sea with seawater as main water source.•There was a clear need to use fertilizer applied frequently into the pots.•Extrapolated yields of edible sea purslane were 10.9kgm−2 yr−1 on a dry weight basis.•This production method can be implemented to produce plant biomass for food without requiring any freshwater.