pretty much right away, they didn't get noticeably bigger to the naked eye after I added it. I would imagine it takes as long to kick in as an increase in nutes, like 2 days. I have had good results with 1/4tsp/gal I think. One time I put a bunch in, i dont remember how much, but it burned the leaves I think. This was my ES mother if you recall.
Hope it does the trick for you.
Hope it does the trick for you.