Going green with green roof shelters

By Ted Schaaf
Gardens on Spring Creek

The Homestead Act of 1862 brought settlers by the hundreds to the American plains. Because trees were scarce, settlers turned to sod to build their homes. One could say these were the first green roof shelters in America.

Benefits of green roofs are threefold: Plants provide life-giving oxygen. Planted roofs filter stormwater by slowly releasing surplus water. Green roofs moderate heat islands that traditional roofs create as the sun is absorbed into them.

From a gardener's standpoint, green roofs are beautiful. After all, gardeners have planted plants in every other conceivable location. Why not plant roofs?

Preparing the roof

Designing the green roof at the Gardens on Spring Creek required engineering by a contractor with knowledge in green-roof construction. In order to keep soil in place on the sloped shelter, a specially designed egg crate plastic was installed over the surface of the roof. A gritty soil, which is more rock than soil, was added to the roof to a depth of about 2 inches. A drip line was then installed with emitters spaced at 12-inch intervals. This allowed for easy planting on 12-inch centers. Once the mechanics of the green roof are finished, the next step is plant selection.

Selecting plants

Most green roofs use plants with the following attributes: Plants should be low-growing or spreaders. Plants must exhibit high drought tolerance. (This is especially important here in the West.) Plants should have a fibrous root system and need to be low maintenance.

If all of this sounds familiar, it's because this is the same description for groundcovers. Groundcovers are enjoying a surge in renewed interest thanks in part to green roofs that depend on them to provide adequate coverage. They are useful in covering bare soil when a grass lawn is inappropriate as in densely shaded areas or areas with steep slopes. Groundcovers are also especially suited to this arid climate.

Groundcovers

The groundcovers most often used on green roofs are sedums. These "tough as nails plants" hold up well to the harsh roof environment. At the Gardens, I chose an assortment of groundcovers for our green roof shelter. After all, a monoculture of plants rarely occurs in nature and for good reason. Dwarf varieties of plants that were successfully used on our roof include sedums, yarrow, native pussytoes, ice plant, candytuft, dianthus, gold alyssum and creeping potentilla. These plants were repeated on all four sides of the shelter, weaving a beautiful tapestry of color from early spring into late fall. Sedums provide that splash of late season color as their foliage changes color.

Maintenance

As with all landscape plantings, occasional maintenance is needed. Yes, weed seeds have found a way of seeding themselves onto the Gardens' green roof. Three or four weedings per season is, however, enough to keep the roof weed free. I also spend some time on the roof each season removing spent flower heads on many of the groundcovers. Although irrigation times vary, a five-minute daily watering is generally sufficient. If summer showers ever return, I'm sure these plants could survive on far less irrigation.

The shelter in our children's garden provides a nice respite from often stress-filled lives. It is also a wonderful shade structure where families can enjoy a picnic lunch.

Something to keep in mind is that the 300 plants growing overhead are providing a greener future. Fort Collins is fortunate to have the only municipal green roof shelter in Colorado. Stop by the Gardens soon to enjoy it.

Ted Schaaf is the horticulturist for Fort Collins' Gardens on Spring Creek, located off Centre Avenue about a half mile south of Prospect Road.