Why does water condense on grass and iron grills in cold weather? In my book it is said that in cold weather fog appears. This fog is nothing but water droplets. After a hot day if the night is cold then the moister in air starts to condense. What I do not understand is why does water condenses heavily on specific places like grass and iron objects only? I first thought that since iron is good conductor of heat so it becomes cold at night early which then captures nearby moisture more effectively than usual objects. But then grass is a poor conductor of heat. Another thought is that most of the objects absorb water. Those which do not absorb are metals and grass. 

Please explain.
While grass IS a poor conductor of heat, it is super thin and will cool off really quickly because of of that alone. The increased surface area also means a greater area is exposed to the night air during the time when the moist air drops to the ground and will thus collect more dew than maybe a stone or a tree trunk.