You can always add it later as a top dressing or "tea." If it's mixed into your growing medium you are going to be stuck with it. Too much of it and your soil we be like slippery, wet clay. Drainage and proper aeration are critical, and worm poo can be problematic if you're over-zealous. Note that carinia offsets 10% worm poo with 3x as much perlite. :thumbsup:

And if you're staying in dirt, use Rapid Rooters like Shake suggested. Almost foolproof. Unless you're growing hydroponically, starting in rockwool makes very little sense.

Bossy, ain't I?
DH