Green Roofs
Green roofs are a relatively new concept to North America and it is important to distinguish between the several kinds of systems that are being discussed.
Types of systems
1) intensive green roofing systems
2) extensive systems and
3) vertical coverings
All three systems come with advantages and disadvantages. Here’s a summary:
Intensive systems
These are characterized by having a deep soil base that means a higher load on the roof but a wide range of plants that can be grown. (including trees and shrubs) It also can mean higher maintenance costs. You can essentially grow anything you want on a building that has been designed to handle both the soil weight and the plant weight. Irrigation is installed and the weight of the water is also engineered.
Extensive green roofs
These are shallower soils, less expensive to install, have far fewer plants that will survive and are cheaper to maintain. Fewer plants means hardy plants that do not require deep soils – mostly alpine or ground cover types. Most of these systems are installed with very shallow soils and sometimes the vegetation is allowed to spontaneously develop and maintain itself. This quickly gives a roof of grasses and at least initially – flowering weeds such as dandelions. These roofs are not irrigated so plants are on their own.
Plants that are xeric (able to live without a lot of water) do very well in these conditions and an initial planting will quickly establish itself. Check out the pages on full sun perennials for some ideas.
It should be noted that without maintenance, any green roof is going to appear weedy after a few years. It will NOT look like a magazine photograph of a well tended garden.
But your house will be cooler in the summer and warmer in the winter.
Vertical coverings
Designed to cover walls rather than roofs when these plants are grown in the ground (such as vines) they can quickly cover a wall and provide environmental protection from winds etc.
If grown in balconies, the same plants can be grown but modifications to the growing systems have to be made ( the use of annuals instead of perennials, winter root protection etc). So apartment balcony gardening systems are important here.
Vines and espalier fruit trees can quickly protect a house from winter winds and summer sun, modifying internal temperatures in a positive manner.
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