Why is more dew formed on a grass and not on polished metal surface

Answer

Incidentally, they all form dew but because grass is closer to the soil, which maintains heat longer than the air where tree leaves are found, you will find more condensation in that region. Also, higher up the wind and sun will allow faster evaporation which makes the dew less noticable on tree leaves.

Explanation:

Preferred objects of dew formation are thus poor conducting or well isolated from the ground, and non-metallic, while shiny metal coated surfaces are poor infrared radiators. ... If the wet soil beneath is the major source of vapor, however (this type of dew formation is called distillation), wind always seems adverse.

aquifers are bounded above and below by impermeable rock. the driving force of groundwater movement in confined aquifers is pressure, rather than gravity.