I'm coddling two new plants grown from seed. They're doing great and look perfect. I had some issues outside and moved inside to better control their environment. I haven't fully finished setting up my tent. I currently have them under 18w LED 3 blue/3 white. Plants are about two inches tall. Great color. How long can I leave them under these lights before 18 watts will no longer be sufficient? Thank you for your help.
heavy on the blue for veg and heavy on red for flower, generally it will depend on how large you grow the plants, often dictated by your grow tent or grow space. Normally I would recommend 60-80 watts (LED) per plant during flower for plants up to about a meter tall. For veg you can get away with about a third of that. During veg your plants will start to reach for the light (stretch) if they are not getting enough light or an incorrect spectrum. The light you have and the space (cardboard box?) is good for seedlings and clones but I wouldn't get my hopes up for anything else. Besides your color is wrong for flower anyway. My advice, buy a 2x2 or 3x3 tent and a proper 100-200 watt COB based (3000-3500 kelvin) LED light or a Quantum board.