Actualy, I have kept an mj plant without any light or ventilation for 3 weeks once...without harming it. I had too many clones (rooted in rockwool cubes) and put spares in a black refuse sack, knoted it and chucked to the corner of the room till i had more stuff to put in it before dumping it. 3 weeks later i open the bag to put more crap in and I see the clones are perfectly healthy, lush and green, without so much as an upturned leaf or red stem...I was amazed. I wasn't amazed they were stillalive but i was amazed how well they looked all in a heap. It was SS Chronic which was great robust genetics but poor smoke imo so I have her no longer...