By default, the grid will always be printed in portrait orientation. In order to print the grid in landscape orientation, you need to create a new instance of the GridPrintDocument class and set the DefaultPageSettings.Landscape property to true.
Demonstration
The following examples demonstrates how to print the grid in landscape orientation:
Keep in mind that if you call the grid'sPrintorPrintPreviewmethods, the grid will always be printed with the default print document (and therefore in portrait orientation).