De or het winterhardheid?

The correct Dutch article is:

de winterhardheid

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

How to use winterhardheid

the winterhardheidde winterhardheid
this winterhardheiddeze winterhardheid
that winterhardheiddie winterhardheid
our winterhardheidonze winterhardheid
your winterhardheidjouw winterhardheid
every winterhardheidelke winterhardheid
which winterhardheid?welke winterhardheid?
a big winterhardheid / the big winterhardheideen grote winterhardheid, de grote winterhardheid