American Dictionary of the English Language

WELK, verb intransitive [G., to wither, to fade, to decay; primarily to shrink or contract, as things in drying, whence the Saxon weole, a whilk or whelk, a shell; from its wrinkles.] To decline; to fade; to decay; to fall.

When ruddy Phoebus gins to welk in west.

WELK, verb transitive To contract; to shorten.

Now sad winter welked hath the day-- [This word is obsolete. But its signification has heretofore been misunderstood.]