Roof gardens, as you might imagine, are gardens installed on rooftops. Rooftop gardens are especially common in urban areas, where space for cultivation of ornamental and edible plants is limited, but they can be found in other regions, as well. Depending on the people doing the cultivation, a roof garden may be purely ornamental, as in the instance of the landscaped gardens which surround rooftop pools at prestigious hotels, or it may be more functional, providing an assortment of fruits, vegetables, and herbs. Mixed gardens with elements of both are not uncommon.
People have been taking advantage of the space on their rooftops to garden for thousands of years. Archaeological sites in parts of the Middle East and the American Southwest, for example, show that many villages had thriving worlds on their rooftops, with some communities even traveling from rooftop to rooftop, rather than along surface paths and roads. Roof gardens are especially common in temperate and hot climates, where the rooftop is a pleasant place to be for most of the year.
In most cases, a rooftop garden is a container garden, but this doesn't necessarily restrict the gardener. Fruit trees such as lemons can thrive in a rooftop garden if given big enough containers, as can climbing vines like kiwis, and bushes and canes such as raspberries and blueberries. Vegetables such as carrots, squash, and potatoes can be grown in raised beds on a rooftop with ease, as can many flowers. In the case of a home with a living roof, the rooftop garden is the roof, although special measures may need to be taken for deep-rooting plants like trees.
In cities, roof gardens aren't just attractive to look at. They also positively benefit the environment, by cooling the air and scrubbing impurities. Many buildings designed with ecologically sound principles in mind feature roof gardens, and the garden can be a pleasant place for residents, workers, and visits, with the plants providing shade, pleasant smells, and a hint of nature.
The size of a roof garden can vary widely. Some gardens are small by necessity, because of the design of the roof, while others may sprawl out across most of a roof. Access to the area where gardening is being carried out is critical, as is access to water for irrigation. In communities where roof gardens are common, many contractors build in storage containers which can catch rainwater for the garden, and a greywater recycling system can also be used to provide water for a roof garden.