In due time.
I know that that's not an exact measurement of time, but it'll have to do. Baby locks have between 1-3 inches of straight hair at the roots. They will lock up, though. When they are mature, it shrinks to about 1/4 - 1 inch of straight hair.
Locks go through 3 main stages. First they shrink a ton. This when much of the actually knotting is taking place. Then they go through a stage where they seem to no grow at all, but they don't shrink either. This is the stage you are looking for. That when the roots really start matting and knotting up. Then they grow like crazy.
I'd say around the 6th month (average), is when you see your roots really start to tighten