Preparing the Field
A piece of styrofoam insulation works well for a scenic base. The wire stalks will press in easily and remain upright. Keep in mind that the stalks will be closely spaced, so there is no great need to detail the entire base. A coat of brown or black latex paint is all that is required beyond the first two or three rows.
Mark the rows of corn with a pencil. Keep the contours of your scenery in mind. Most farmers plant across a hillside to prevent excessive runoff. Run your rows accordingly.
Add a thin layer of dirt to the perimeters of the cornfield. You only need to go a few rows deep.
Simply press the wire stalks into the foam to plant. Keep the spacing tight and the rows parallel. You can easily make up for any slight height differences at this point as well. It is easiest to start at the back and work forward.
You will probably be surprised at how many cornstalks you're using. Even a modest field can consume hundreds of stalks. If you run out, simply go back and make more. You probably won't have a really good idea of how many you need until you get started.
In a little time, you'll have a detailed cornfield that will be the envy of many modelers...none of whom will believe it started as a Christmas decoration.