This is a common question!
When you are growing a plant from seed, and finishing it at about 3 feet tall, you should expect to transplant at least twice during the grow.
Why is this?

-Losing light to the soil surface is undesirable, so having small pots and a continuous canopy is more efficient.

-Letting the plant focus too much energy underground is inefficient- the roots SHOULD go out to the sides of the pot and just chill there for a while while the leafy part grows.

-Unused soil zones within the pot can be wet and stagnant where the roots can't access the moisture in them. That's no good.

-When you are, as many many growers are, growing in a peat based medium, you want to MINIMIZE the amount of time that new roots are in old soil. When a product such as promix is packaged, it is buffered with lime to bring the pH up from the natural pH of peat (4.5-5.5 or so) into a more suitable range for common plants. That lime buffer is good for only so long after water has been added and it starts to react with the acids in the peat. After a couple months or so, many growers will note a SHARP drop in pH and sudden lockout symptoms. One way to avoid this is to constantly be potting up and refreshing the soil AROUND the root ball so that fresh roots can access fresh soil.

I hope that helps.
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"Careful what you carry- 'cause the Man is wise- you are still an outlaw in their eyes" -Steely Dan
"Multiple pieces of anecdotal evidence do not equal scientific fact." -Rhizome
"If the Queen Bee ain't happy... the hive isn't happy!"-Dutch Pimp
http://boards.cannabis.com/basic-gro...e-harvest.html<-It's a grow guide! Enjoy!
http://boards.cannabis.com/plant-pro...hy-how-do.html <- all the boring stuff about soil chemistry you never wanted to know
http://boards.cannabis.com/grow-log/...ml#post1837597 <-how to make canna caramels
http://boards.cannabis.com/grow-log/...ml#post1820481 <-illustrated cloning guide permalink
Contacting Her Dankness: stinkyattic at hushm4il-please use the same discretion you do on the boards, thanks.
I don't claim to know the first thing about growing anything; hell, I can't make a Chia pet sprout.