Abstract: The cultivation of terrestrial plants in brackish water or seawater is carried out with this invention. A light-weight, floating growth medium package (FGMP) or, alternatively, a sheet of suitable material is used to support the growth of terrestrial plants floating on water bodies of various salinity, including 100% seawater in marine environments. The FGMP units can be linked together and confined in a floating, rigid or flexible framework to form a floating seawater cultivation platform (FSCP). Using the method, plants were able to grow and thrive on the FSCP floating on 100% seawater in a sustainable manner. Halophytic akulikuli (Sesuvium portulacastrum L.) can regenerate its shoot and root in seawater. Thus, the discovery will enable us to practice marine agriculture, or agriculture on the sea. The FSCP can be used for wide range of purposes, from environmental protection to landscaping to crop production.