I'm growing a sativa dom. strain right now for the first time. Things are taking a bit longer, but it will be worth it in the end.

Some of the like to spiral out of control too, seriously! I started flowering this Afghan #1 x Jack Herer when it was maybe 10 inches in height, and the bugger has reached 3 ft now, and it's not near done flowering.

So if you are going to grow a sativa, make sure you have all the extra headroom you can get because they are much taller, and are lankier than indicas.