Question about early flowering.

I have a small grow box that is 3 feet tall in the compartment I am wondering two things:

1. What is the earliest a plant is able to flower? Some say 1 month vege, some say 2. What is a safe bet?

2. How high will these plants grow while in floweing? I've heard they double in height?

If you flower early they will triple or quadruple in height. You can start from the very beggining if you want. I would suggest at least a week or two of veg but not much more than that if you have a 3' ceiling. You will either need to LST, top, scrog, fimm or really really pray for a short variety as well.

Here's an old grow I did. This is the day I flipped to 12/12 (2 week veg):


Finished plants ended 2.5-4' with them averaging around 3.5'

Hey,

Generally, it takes about 5 weeks of healthy growth under good lighting to have a plant ready to flower, if growing it from seed. If you run your lights 18/6, they'll pre flower as soon as they're mature.

As for your 2nd question, 'these' plants all depend on the strain you're growing for their mature height. Within a strain, you have different phenotypes, so that means all White Widow females (for example) won't look or grow the same. Jack Herrer strain has 4 different phenos, only one of which is short, indica like. With the hybridization of cannabis, you have indica x with sativa, and then the final product is marketed as a 'strain'. To the point, you're always going to have sativa traits (tall and stretchy) showing up in viturally every contemporary strain. (this is also why hermaphrodism is so prevalent in cannabis)

To be sure, there are plenty of phenos that will fit in a small area like you describe, have dense growth, good yields, and potency. It would be nice if you had a more open area for the selection process and could then do your final growing in that 3' spot. Also, consider the ventilation needs.

Edit: The above post came in as I was typing this, and I would say that this is a typical height for many plant types. Nice plants too.