Well ive never really seen a hole that was too small. But the thing to think about is the smaller the hole the faster the ducks eat out the food. So when it comes to season time you have a hard decision as to how early to flood your hole to get ducks in there. If you flood it early you will have a heck of a shoot the first weekend but by the third weekend its all eat out. But if not then you may not have that killer first hunt. But it all just depends on the location really. I mean ive seen private places no bigger than a 1/2 acre that they flood corn and still do ok during the season hunting it sparingly. But its hard to say how small is too small if you know what I mean. Private duck holes are all about location and how long they have been flooding.
We have places that are anywhere from an acre up to 200-300 acres and some of the best places are the smaller ones. If you hunt them sparingly and flood them at the right time and the ducks are there you shouldnt have a problem killing ducks anytime you hunt it. We have had good luck with millet holding ducks in some holes longer then corn does if you have the option to plant some millet. We are going to try a little bit of rice this year and see how it works out for us in an area that stays really wet year round.
The thing you have to remember with millet is it has a very fast decomposition rate...ie..rot. Tnduckman is correct though, birds like it, but a lot of times there not in there for the millet itself. With the thick vegetation that millet produces, its ideal for all the microorganisms (insects, plankton types)that ducks love during warmer times when "hot foods", such as corn and milo are not favored.
I've hunted swamps where guys threw out 50lbs of millet in a swamp in June/july over 1/4 acre opening. They killed ducks all season, but they hunted it sparingly. Warmer than average winters and early season, ducks will tear it up. Extremely cold season....not so much. But nowadays, its about impossible to guess what the winters are gonna be like.
The field is on the TN river and has two small ponds to the rear of the pit with an open field on the other side. I just need to figure something out to get the ducks and geese to come off the refuge and want to land there.