Planning for a Container Garden on a Roof

摘要

Water does not seek it own level when it has to flow through gravel, rocks, or man-made drainage mats. Over the years, I have been involved in solving a number of cultural problems associated with roof- top gardens that have been built on existing roofs. It seems like a nice idea, but unless a roof is designed with a pitch of at least 1 percent and has been equipped with the proper membrane, you had better limit roof-top gardens to planting in raised containers. The friction caused by drainage systems restricts the free movement of water, thus causing it to accumulate unless the drains are very close together, possibly 5 feet apart. Few plants can tolerate growing in saturated soils, and gravitational water moves more easily down slopes than it does horizontally.