Minimum amount of light to keep a plant in veg?

Hi, bit of a weird one, but i started a greenhouse grow in northern UK in august cause im an idiot and wanted to see what happened (free feminised seeds, no big loss). So now i've got 4 healthy month old plants looking happp, but they arent gonna get much heftier by the time the light starts to fade - By my maths we'll hit 12/12 from the sun by the end of september. 3 i'm using to practice diffferent techniques see if any produce even a tiny bit of yield. I want to take one though, and keep it indoors next to the minimal amount of light 18/6 to keep it alive and in veg so i can move her back outside in march.

Current plan is just to put it in my wardrobe with maybe 3 low power cfl's and move it to the windowsil on sunnier days, so my question - is there a rule? like lumens per sq/f or something to keep a plant from trying to flower.

I'm not expecting much if anything from them to be honest but thought it'd be interesting to try and carry one over to spring

cheers

Im in northern maine, second coldest place in the states and ive had plants flowering in under 13 hrs outside, so i think its approximatly around that 12-13 hr range.

Depends on how big the plant is you want to keep.

I would suggest to go a other route bro.

Take some cuttings of the plant and let them root indoors.
Use the strongest two rooted cuttings of the batch from here.
After that use the bonsai method to keep em small.
you can keep them in a very small cabinet with a 10-20w cfl (a diy reflector can be added) plus a small 50mm terarium fan (looks like a tiny computer fan) as an exhaust and passive intake.
Cut the new growth back on a regular basis. I use 24/0 lightcycle.
Dont fertilize much.
in spring you let the plants grow out a bit more so you can take some cuttings.
timing should be considered. I WOULD NOT BRING THE CLONES OUT BEFORE END OF MAY.(daylenghts)

I would keep the bonsa-mother this way until you harvest the clones in the fall and testsmoked them.
If its fire you still have the bonsai-mother around to work with in the next season.

^^ I hope this helps

Peace

I keep little clones on the floor of my flowering room for 12, then keep it on my oven under the tiny little light on the range hood to keep it from flowering.


Not how you'd want to veg plants but it doesn't take a lot!

Outdoors plants will flower before true 12/12 hours typically

Four.
It requires Four Units of N light to keep X plants alive, you will harvest a pound.
Sorry, I couldn't help it.
@Gbuddy has the right plan.