De or het grashelling?

The correct Dutch article is:

de grashelling

Rule Words ending in -ing: almost always de. See the rule

How to use grashelling

the grashellingde grashelling
this grashellingdeze grashelling
that grashellingdie grashelling
our grashellingonze grashelling
your grashellingjouw grashelling
every grashellingelke grashelling
which grashelling?welke grashelling?
a big grashelling / the big grashellingeen grote grashelling, de grote grashelling