Built in autumn 2007 and in it's fourth growing season, the Denver Botanical Gardens green roof is an exemplar arid/dry green roof in the heart of the mile high city. As of May 2011, according to Amy Schneider, who looks after the roof, there are 113 species of wildflowers and plants on the roof.

The plants represent those associated with landscapes of the steppe climates of the South and Western America. The plants represented onthe roof are those that have evloved to relish the arid, cold hardy, xeric, low nutritional requirements, and  high elevations of the 'steppes' found in Colorado.

The design of the roof has taken into consideration a maintenance regime that has no fertilisation or heribicide use. The plants are bedded into an expanded shale based growing medium/substrate. Although the roof represents the dry arid areas of the South and Western north America, there is naturalistic 'desert' garden feel to the roof.

Below are some of the plants that have been sued on the green roof.

Woody shrubs:

Dwarf/Fragrant False Indigo Amorpha nana - grows in dry prairies and rocky hillsides

Rabbitbrush Ericamera nauseosa - associated with  arid regions of western North America

Hairy Mountain Mahogany Cercocarpus breviflorus - Mountain Mahoganys native to the western US northern Mexico, where they grow in chaparral and semi-desert habitats often at high altitudes.

Trees

Desert Willow - Chilopsis linearis - native of southwestern US and Mexico

Herbaceous perennials:

Red or Hummingbird Yucca Hesperaloe parviflora - desert native of Texas

Chrysanthemum weyrichii, Delospermia, Dianthus and Opuntia

Delosperma, Dianthus, Opuntia...

The researchers at the Botanical gardens are studying the plants to see how they before in the context of green roof. Each plant is given a performance rating and these ratings are being expand to include areas such as spread, height, flowering time etc. Such research will allow designers to be able to better understand how and what performs best in the context of an arid/dry green roof in Southwestern US.

Irrigation is of course and issue and this is being monitored. Generally regular irrigation commences in late July through the growing season until the snows come in the fall.

Whilst livingroofs.org were there visiting the roof Honey bees were actively using the green roof along with a number of other native pollinators.

The green roof is open to public so if you are in Denver it is a recommended visit.