Come on now guys....am I gonna hafta put ya'll nose to nose?
I cant explain exactly why too much nitrogen does what it does to plants. All I know is that our babies dont like too much of it. Like Lucky said, making your own soil, or buying some with no ferts in it makes SURE that the plants ONLY get what YOU want them to have.
I re-pot my plants once they get their 3rd true's. At that time, I put them in my own mix, which DOES include a top soil made by Sta Green. (Its exactly like MG, just a couple bucks cheaper.) But, it's such a small amount, they get the tiny bit of nitrogen they need. They actually get MOST of their ferts from the manure. But yet again, its not the biggest ingredient in my soil. Peat moss is. It's your babies best friend. This year I'll be going to Pro Mix IF the ONE Ace Hardware around here can get it shipped in. If not, then its back to my own again this year.
The best reason for having a soil with no ferts in it is because IF you have a problem, like the one you are having now, you can try one thing at a time to see if it helps the plants. If you didnt, you would be throwing in a mix of different nutes, possibly going OVER board with one or more. Kinda like one step forward, two steps back, you know?
Im no expert by ANY means. I like to keep things as simple as I can. When you can learn which ferts do what, and how your plants react to each individual one, you will be a MUCH better grower, and will have AWESOME plants with TONS of pods. Know what I mean?