I spoke with Architectural Review and they said to submit a photo similar to what you plan to do and a form located on this page
VCDD Architectural Review before installing the window boxes.
Whether it is a pool addition, landscaping, painted driveway, porch enclosure, coloring of walks and/or driveways, arbors, pergolas, trellises or removal of trees that are greater than four (4) inches in diameter it is necessary to submit a Modification/Alteration Form for approval.