I've been going back and forth with this phrase with a lot of people, and we are pretty evenly split: Does this mean to open or close the curtains? Or can it be either? Draw them open vs Draw them closed?
I reckon it can mean either. "Draw" in this context means roughly the same as "pull", and doesn't say which way to pull them (which would usually be easily inferred from context).
From Webster's Revised Unabridged Dictionary (I found this on a website I'm unfamiliar with, so I can't directly vouch for the validity of the citation):
however, in common usage [speech/dialog], it most often means to close them... such as in: He drew the curtains, not wanting to be seen from the street. "Quick, draw the curtains, Jefferey!" The curtains were drawn when they entered the room, the corpse lying in a puddle of light from the single lamp. ...and so on...
I think it comes from an old word which means just 'pull', but I'd use 'draw back' to mean open, and 'draw' to mean close.
If it were ambiguous then I'd use "draw back the curtains" for open, too, but I'd use "draw the curtains to" for close (but I suspect that that's a regional British idiom).
Well, if it's ambiguous, and you have a hard time making "draw" unambiguous, simplifying to "open" or "close" might be the best option. Try to avoid ambiguous words that can't be resolved using context.
Thing is, if you're standing in the room it's not ambiguous because you can see the current state of the curtains. But your reader isn't standing in the room.
