As far as I know CGM works by desiccating the soil surface to prevent germination and maybe even kill a new seedling lacking much in the way of roots.

I would imagine within a couple rains or waterings it would no longer be effective and you could seed.

According to the people at Iowa State University where the weed growth suppressing properties of Corn Gluten Meal were discovered the affects in the soil last 5 to 6 weeks and the material works to prevent the formation of a root on the germinating seed.

Here is a link that might be useful: Corn Gluten Meal Iowa State

I may have already posted this casual observation here. I bought some 'wild bird feed with corn gluten' and I tossed a handfull and raked it in a bit and watered and got at least six different varieties of plants growing from wild bird seed; mustard, two different sorts of sunflowers, two or more different grasses and something as yet unidentified.

There was no discussion on the label as to why the wild bird feed contained corn gluten. Perhaps it was for the birds.

was this meant to be eaten as seed or to grow plants to feed the birds? If the former I have no idea why the gluten, if the later, it was probably intended as a nitrogen source (10% N by weight).

My understanding of CGM is that it works best watered in once and then the area be kept dry. Applied in a rainy season it isn't effective. The reason, according to my understanding, is that it acts as a desiccant so regular irrigation negates it's effectiveness.

Regular irrigation dissolves it into the soil where soil bacteria eat it.

I bought my wild bird feed with gluten from the supermarket so I expect they were selling it as feed rather than seed.

Here everything must be irrigated so, regardless of the reason for the gluten, it would have been regularly watered.

Hmmm, I wonder if they include the gluten in an attempt to prevent the seed from germinating. I know I love feeding the birds, but I don't much appreciate their scattering the seeds all over the gardens.

Can't imagine it would actually work in this case though.