Can I pick up the blue moss?

Hint 1 of 7:

Yes you can, but you can't carry it in your bare hands.

Hint 2 of 7:

You'll need a container for it.

Hint 3 of 7:

A jar might work.

Hint 4 of 7:

Or even something that's ajar.

Hint 5 of 7:

Have you stood on the metal pad in the barrow yet?

Hint 6 of 7:

Doing so will transport you to a new section of the barrow.  You should find
a "door ajar" down there.