Two years ago (on May 9, 2008) I helped install a green roof, along with other master gardener volunteers, at A3C Collaborative Architecture in downtown Ann Arbor.
The roof serves as a demonstration and research garden that highlights many possible green roof options. Different sections showcase various plant types (meadow, alpine, and park), planting techniques (tray, mat, and monolithic/plug), and watering systems (irrigation and rain water only). The roof also serves to collect storm water which is rerouted as gray water into the building interior.
The trays were provided by LiveRoof and our installation training also certified us in the technique!
The plastic trays hold the medium and plants, and sit, as a whole unit, on top of the roof membrane. The sides of the trays lock together, but we had to be careful to orient the trays correctly so the proper sides interlocked. And the trays were heavy--25 pounds! The plastic around the edges is removed after trays are put into place, so the plants can spread into one another.
The growth medium here isn't for the trays, which contain their own growth medium, but for plugs planted on either side of the tray systems. It's really important no tiny pebbles get between the roof membrane and the trays, so one volunteer had to sweep while the others put the trays in place. Note the plastic edging being pulled out.
The trays were planted down the center of the roof and contain alpine plants (mostly Sedum). Here is the completed section.
Beyond the tray section, plants were established using a mat/rug system from Xero Flor America (XeroFlora). Volunteers were not involved in this installation, but it's easy to see how the system got its name: The mats come rolled up, like sod, with growing medium and plants already in place and are simply rolled out on site. XeroFlora also did the green roof at Ford's Rouge plant.
On either side of the tray plants, volunteers planted plugs and larger plants directly into the growing medium. This is the corner of the park section, with a little patio out of sight to the right.
The soil medium in which the plugs were planted is 93 percent inorganic. This prevents soil erosion (or particle size shrinkage) and soil compaction.
Here is the completed park area.
On the other side of the trays is the meadow area.
Once the trays, plugs, and mat were all in place, they were watered in. Now, an irrigation system waters half of the garden while the other half gets by on rain water only.
Watching you watching me... I had to get this photo of an Ann Arbor News (it still existed then!) photographer, perched high to get all the action.
I went back later that year, on November 19, 2008, to see how things had progressed. Despite the slight snow cover, I could tell things had filled in over the summer and fall.
I love rain chains.
Look how the grasses have grown in the meadow side!
Everything looks lush in the park corner...
And in the park area overall.
Some Dianthus deltoides 'Firewitch.'
It's high time I visit again. I bet the plants have grown by leaps and bounds in two years! I've marked my calender for August.