What is the best size for marijuana plants to start flowering?

I have my marijuana flowering in a cupboard that’s 18” x 4” and is lit up by a 250-watt Son T Plus HPS lamp (6 total square feet at 41 watts psf). The upper part of the plants (3 to 4 plants tops) starts to bud off. I flower the marijuana plants at 14 inches and they generally grow about 2.5 to 3 feet after that. Some of my leaf and stalk areas are wasted. Do you think it’s a good idea to force them earlier (say, at 9 inches)? Will I yield as much if the plants aren’t as big when I start flowering? There are little side-shoots on the plants that have leaves and small flowers. I don’t know if I should get rid of these leaves and side branches, because they are still green despite being shaded. Might I get bigger buds if I strip these branches? My gut tells me to leave as many leaves on the marijuana plant as possible.

9-inch marijuana plants likely won’t grow as many side-shoots as 14-inch marijuana plants. You won’t get as much of a yield, but you can space the smaller plants close together (between 4 to 9 plants per square foot).

In this case, the yield should increase per square foot. If you take away the lower branches, the growth in the upper canopy will increase because all the resources go there. If they are left on the plant throughout the flowering period, the shaded lower buds won’t be developed at the time of harvest. You can let them finish after the harvest, but this is generally not worth the wait.