"Actually looking at Scott's Turf builder... 30-3-3, an 18 pound bag feeds up to 5,000 square feet. For 10,000 sq ft that's 10.8 pounds of Nitrogen! Compared to just 4-5lbs for the corn. Corn is a moderate amount compared to commercial ferts."
????? Did you fail math class, logic class or both? As you say, Turf Builder supplies 10.8 lbs of N for 10,000 square feet. That's 1.08 lbs per thousand square feet. Are you with me so far?
Corn gluten varies between nine and eleven percent actual nitrogen, so let's just say an average of 10%. Are you still with me? It takes between forty and fifty pounds of gluten per thousand square feet to provide a noticable level of weed suppression. Are you still there? Forty pounds of gluten at 10% nitrogen equals FOUR POUNDS of notrogen per thousand square feet. It may be slow release, as Ann claims, but it's still way more nitrogen than is healthy for the grass. Can you say Rhizoctonia? I didn't think so. But if you apply four pounds of nitrogen to fescue, rye or bluegrass in the spring or summer you will quickly find out what it means.
Yes, corn gluten will suppress weeds IF USED HEAVILY ENOUGH, but it's also a great way to kill your lawn, or at least make it very sick.