I was worried that I waited too late to apply corn gluten to the lawn last year, so I picked some up at the Farmer's Exchange yesterday. The woman there told me that the best time to apply it was between 20 April and 5 May. (I'm in southern New Hampshire, zone 5.) Is it really a matter of dates? Or should I be looking at conditions?
Other stuff I was told: You want to apply it when the ground is moist but with no rain expected for a while. Corn gluten puts the emerging plants into "drought stress," so rain would compensate for the corn gluten's effect.