Thanks aruzinsky, went ahead and got a small ceramic heater to put in there to keep things at temperature during the dark periods. It will turn on and off with the same controller that handles keeping it cool when the lights are on.

One small thing would be to make the dark period during the warmest part of the day. Also putting them in a grow tent would help retain some of the heat.

• Was curious about that too... thought it would make most sense to run the lights overnight to help offset the heating needs during the coldest part of day (night). Any worry about upsetting some kind of natural rhythm? Worried it may throw them off when i take them outside and sun is opposite cycle? Probably overthinking it! They are in a fully enclosed 2x2x4 box with foam insulation on 4 sides and acrylic doors on the front. I have a venting fan for cooling which seems to be running a lot now with lights on but probably won't much when temps drop into 40's! Would think that would provide as much heat retention as I could hope for? The small ceramic heater seems to work well, blows a gentle breeze of warm air, nothing too hot. My plan- and controllers ability- was to set a single temperature and maintain 24 hrs regardless of light status.

Yes, that sounds like it should retain heat well.

When it gets close to the time to take them outside, you could start adjusting the dark time to put them back it sync. That should work out well. because the temperatures will be warming up.

Ok great- thanks!

Don't bother. There won't be any synchronization problems.

Anyway, if your basement is like mine, its temperature will be slightly higher than the temperature of the surrounding ground which doesn't change between night and day. Same for the temperature of cold water from your faucet after it runs awhile. It will still be cold in the late Spring because it takes a long time for the surrounding ground to warm up.