Sentinal,

Not sure this'll help.

My plant had to go from a 2 gal to a 5 gal (long story) and when I transplanted I raked in about 12ozs or - the equivalent of about 2 and a half cups - of castings into the top couple inches of the new soil in the 5 gal, then lowered the 2 gallon root ball in.

That was about 4 weeks ago.

I added nothing else except the straight distilled water of course.

Since then I have fed the plant Schultz Cactus Plus in increasing amounts and if anything it look to me like the plant still jumped and sucked up a lot of Nitrogen from Schultz despite the worm castings.

Bottom line is I have not seen any signs of a Nitrogen overdose which I believe is what earthworm castings is usually highest in.
rez