How to get a correct height plant?

Ok I have a 400 watt hps for veg and a 120V lumnetek ballast I want my plants say to get around 4 Feet, I heard while doing 12/12 your plants double in size my question is how high should i start doing 12/12 to get a 4 feet plant? I use correct ppm 5.5 ph right conditions temp/humidity

Or atleast a rough estamate?

Switch to flower when your plants are no more than 1 foot tall

dragon24 said:

Or atleast a rough estamate?

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16 inches.

What if I wanted to try and harvest a 20" tall crop?

At what height would you switch from veg to flowering?

mario60185 said:

What if I wanted to try and harvest a 20" tall crop?At what height would you switch from veg to flowering?

Click to expand...

6 inches would be were I'd go. Every plant is different even in the same strain though.

If the plant doubles in size then to figure out high it should be when you flower, then all you gotta do is use some 7th grade algebra to figure out the answer.

Xfeet*2=4feet. solve for X

easy to see the answer is 2 feet tall.


You want 20 inch plants after flowered? then Xinches*2=20inches... 10inches.

alright man I didn't know the specifics on height gain on veg to flower but thanks once my other seedlings get about 1 foot I will switch it to flowering!

No drama....I asked because I hear some say it doubles and some say it more than doubles....so which is it?

Sativas tend to go more than 2x while indicas are closer to 2x. It can also depend on strain and with hybrids, maybe even phenotype. You can also control the height a little with pot size (forcing the plant to become rootbound).