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.