All you need is a depth of about 12 inches of open space against a wall to create a green curtain with a DIY vertical garden kit:
Above: An Easiwall Living Wall panel has a water reservoir so plants can soak up as much water as they need because roots sit above the water line; available at prices from £169.99 to £261.99 per panel from Easiwall. For US gardeners, a similar modular system of EarthBox Mini Garden Planters is available for $59.99 per planter from Newegg.
Above: The modular panels, suitable for both indoor and outdoor use, measure approximately 39 inches tall by 10 inches wide and can be screwed into a wall or attached with ties for a less permanent installation. Use multiple panels together to cover a large wall.
(N.B.: For more, see "World's Biggest DIY Vertical Garden" and "Vertical Garden Kit: The Ideal Ivy.")