Curtain panels are the quick and easy -- and DIY! -- window treatment that will dress your sliding door with color and pattern. Look for long, sturdy rods at home centers, and mount the brackets across the top of the expansive door at even intervals. (Be sure to screw them into wall studs for stability.) Then hang curtains using easy-slide rings or a cord system that lets you draw them open and closed from one side. If you buy a rod that is longer than your door is wide, you'll have room to push the curtains completely off to the side, to leave the door fully uncovered. If your sliding door receives harsh light, you might want to purchase lined curtains, which will block the sun's rays. For a less-than-perfect outdoor view, install a double set of curtains, and use filtering sheers, which you can leave closed, under solid panels. For a finishing touch, cover the top of the curtains and rod with a valance or cornice mounted high enough to clear the door.
For very tailored and functional sliding door window treatments, consider blinds or shades. Vertical blinds have wide metal or plastic slats that hang down from a top rail. When closed, they lie flat against the window and overlap slightly to block the light. You can rotate the slats to open them partially or fully, and you can slide the slats all to one side of the door to get them out of the way. There are also sliding door shades made from natural or synthetic panels that hang flat, usually in several overlapping segments. Each panel hangs from its own track, so when you draw them open, they stack neatly. With different weaves, materials, and textures available, these shades can be transparent or opaque for varying levels of light control. Finally, there are cellular shades with wide vertical pleats like an accordion that you can pull open or closed (or gather in the middle) as needed.
Already wildly popular as window treatments, plantation shutters are available to cover sliding doors, as well. Some slide open and closed on a track similar to the track for the door, and some are hinged to swing open and shut. Narrow or wide louvers -- your choice -- rotate open and closed to let you control the view and light.
All of the sliding-door window treatments mentioned offer light and privacy control as well as energy benefits. For ease of maintenance, there are also window treatments that are part of the sliding door itself. Sandwiched between the panes of glass, narrow blinds or cellular shades raise and lower and tilt at the flip of a switch. Because they are sealed into the door, they never get dirty, never break or get torn, and never need dusting. Another device for light control and energy savings is to add a glare-controlling window film to the sliding-door glass. This can be done in conjunction with another decorative dressing, or, if you don't get direct light and have no privacy concerns, it can be the only sliding-door treatment.