Green Roof Sedum Plantings

I am fascinated by the Sedum (Hylotelephilum as some botanists suggest).  They are hardy, drought tolerant, can switch between C3 and CAM photosynthesis and several native species provide food for endangered Lepidoptera species including the Grey Chi and San Bruno Elfin Butterfly.

There are many native Sedum species considered native to  the US.  Some are even protected by law as threatened or endangered as in;

• Pennsylvania
• Oregon, and
• Kentucky

Green Roofs have been shown over the long term to provide great opportunity for the re-establishment of endangered species.  Green Roofs may provide an important opportunity for those threatened or endangered Sedum species to recover.

There is a wonderful American Society of Landscape Architects article on the web focusing on a Green Roof with several popular Sedum species as part of green infrastructure installed to help the Rock Creek Watershed.

The Sedum's used in the project were;

• S. sexangulare
• S. album
• S. spurium
• S. rupestre
• S. tectractinum
• S. floriferum
• S. kamtschaticum, and possibly others.

From a habitat, stormwater, 'sense of place' and heat island effect, this project was timely and ecologically important, and so too were the Sedum plantings.

Yet as you will read, many of these species are potentially invasive and have been recorded on state and organization invasive plant lists.

Importantly however, Sedum should not be singled out as the only invasive or potentially invasive plant when discussing green roofs.  There are many potentially invasive plants that could be associated with green roofs.  Last year we posted a brief article on the use of Nandina spp. on the Gainesville, Florida Regional Utilities Green Roof (thankfully the Nandina was subsequently removed from the planting schedule).

Here in Florida, Sedum have difficulty with Southern Blight Fungus and tend to dampen off during the long hot and humid summers.  In Jacksonville, S. reflexum appears to do the best on living roofs though it too suffers from the humidity.

Sedum propagates easily according to botanical literature and others, as suggested in the Emory Knolls Farms website.  In fact, spreading cuttings and clippings of sedum leaves and stems is suggested as a quick approach to filling a green roof with more plants.

However, some Green Roof companies raise a red flag about invasive species, such as S. sarmentosum where as the Roofscapes, Inc site indicates;


"The only Sedum that might be considered invasive is Sedum sarmentosum, also known as Star Sedum,Gold Moss, Stringy Stonecrop, or Graveyard Moss. It has green spearhead-shaped leaves, lemon yellow flowers, and long tendrils. We do not recommend using this species."

But it is not just green roof plant nurseries that promote Sedum's ability to grow into full size plants from the tiniest of cuttings, other ecological or nature websites suggest the same.

An interesting article and discussion of Sedum and Green Roofs can be found on the Taking Place website where the article entitled Sedum2 mentions of S. floriferum (one of the Sedum species used above mentioned watershed project);


 I’m careful to throw the weeded stems away in the garbage, because the tiniest little bit of stem or spare leaf will root in where it lands and start growing.  It’s not a problem (so far) here, because I do maintain my garden; I wonder about pieces of sedum escaping from roof gardens or green roofs, and rooting in, say, along a river bank or in pavement cracks.  It’s attractive, but it can cover and smother other plants if allowed. 

Importantly, S. sarmentosum has been considered an escaped and invasive species in Japan, subject to numerous studies.

Any plant that roots quickly from leaves and stem cuttings could potentially escape a roof.  Birds carry plant material from the roof on a daily basis.  Here in Florida as well as other windy areas, wind is a strong potential vector of plant DNA.  Fern spores are known to have been carried across the Pacific Ocean on winds, introducing Asian ferns to the Americas.

I suggest, planted anywhere Sedums will escape and start to naturalize.  How bad this naturalization will become is another question.

As a plant biologist my own opinion is Sedum will initially only naturalize within the disturbed environments of the Urban Core of cities such as Jacksonville here in the southeastern US, because of the humidity and Southern Blight fungus issues.  I personally believe it will have a hard time becoming established in the Florida swamps.

Not so the case elsewhere.

Here in the US there are many red flags and concerns now being raised concerning Sedum use and the potential for invasive activity.

For example;

• The City of Indianapolis cautions against the use of both S. sarmentosum and S. hispanico in the Indianapolis Stormwater Green Roof Technical Design Manual
• The Invasive Plant Association of Wisconsin lists S. acre and S. purpureum as having invasive qualities
• Missouri's Exotic Pest Plant list includes S. sarmentosum as a category B exotic present in Missouri
• Virginia's Department of Conservation and Recreation ranks S. sarmentosum as an invasive species
• Massachusetts suggests it is necessary to gather additional data on the S. telephium as part of the Managing Invasive Plants program.
• The Great Lakes Indian Fish and Wildlife Commission list Sedum spp. as a terrestrial  invasive
• Wyoming's Natural Diversity Database report lists S. acre as a noxious weed plant located across F.E. Warren Air Force Base
• New York's state Early Detection Invasive Plant Program lists both S. sarmentosum and S. telephium species
• U.S. Fish and Wildlife Service list S. telephium on their invasive plant list
• S. acre, S. albo-roseum, S. purpureum, S. ruprestre and S. sarmentosum are listed as Alien Plants by Illinois' State Museum site
• USDA Forest Services, Non-Native Invasive Plant List lists S. telephinum/ S. purpureum on their Invasive Plant list
• US Natural Resource Conservation Service maps naturalized and escaped non-natives, including Sedum.  Their database of non-native Sedum species occurrences is informative.  They suggest "These plants are introduced to some part of the PLANTS Floristic Area, though they may be native in other parts. While many are harmless or beneficial, others that are not already invasive or noxious have a high potential to become so in all or part of their range. In general, introduced plants are likely to invade or become noxious since they lack co-evolved competitors and natural enemies to control their populations."  Sedum species listed include;
• S. acre
• S. aizoon
• S. album
• S. dasyphyllum
• S. dendroideum
• S. hispanicum
• S. hybridum
• S. kamtschaticum
• S. linare
• S. mexicanum
• S. ochroleucum
• S. praealtum
• S. refluxeum
• S. sarmentosum
• S. sexangulare
• S. spurium
• S. stoloniferum, and 
• S. ternatum

Other Countries too, view Sedum species as an invasive plant, including;

• Poland, New Zealand, Switzerland
• Czech Republic
• Japan - see above
• New South Wales
• British Columbia
• Ontario Society for Ecological Restoration
• Canadian Wildlife Service
• Mediterranean regions
• and many others

Many Not-For-Profit organizations and preserves also consider Sedum to be potentially invasive. A few include;

• Nature Conservancy of Canada - Garry Oaks Ecosystems lists S. acre as an established invasive species
• Wisconsin Botanical Information System tracks county by county where the many different Sedum species have escaped and become naturalized
• Washington State University Extension Blog has a comment " My plant peeve right now is sedum. It's used and promoted extensively for green roofs and rooftop garden use, because it grows so well in extreme conditions -- which makes it also quite willing to grow in not-so-extreme conditions. I planted a handful that a neighbor had given me, and it now has spread through one garden bed, along the base of a rock outcrop on the other side of the yard (I took a snippet and parked it from the bed onto the outcrop, not knowing how it would spread and spread), and now is moving into the lawn. It's easy to pull out, but a tiny piece will root, so composting is out, and vigilant disposal is necessary. I have yet to see sedum on an invasive species list, but predict that it will show up on a bunch of them in the next few years, as pieces make their way off of rooftops and into the on-the-ground landscape. "
• Mid-Atlantic Gardener's Guide says 'Many smaller sedums are invasive..."
• Grassroots websites suggest Illinois' Draft Invasive Plant documents list both S. sarmentosum and S. telephium are invasive
• The New York Botanical Garden's notes S. sexangulare has been newly noted in the Torrey Range as an exotic species

Yet Sedum will continue to be used across Green Roofs here in the US and the World.

The issue is not really about Sedum.

The issue is one of native plants and exotic, introduced landscape plants.

Do we feel comfortable with the practice to replacing native plants with introduced species because the introduced species are easier to use, hardier and more resilient (maybe because of the lack of natural predators)?

I believe Sedum can be managed appropriately on Green Roofs.  Rooftop growing areas can provide habitat for those native Sedum too, offering protection for those endemic plant species threatened by monoculture takeover of exotics.

The key component to successful exotic Sedum usage is awareness of its plant biology, maintenance practices, local exotic and invasive species management plants, state and federal laws and proper coordination with state and local Native Plant and Invasive Plant organizations.

Many of the lists above are not law.  Sedum is not illegal to use.

The lists above caution us to take account of our practices.

Changing the constituency of Nature can be a dangerous act.

Sedums on a Green Roof or Living Walls? Should I use Sedums in Florida

Today I am going to take a leap of faith here, stretch out my neck and say "Yes - Plant Sedums and Succulents on your Florida Green Roof!"  However there are several important qualifiers to this statement.

First of all - let me show you what will most likely happen once you plant a succulent or sedum on most of the vegetated roofs I've seen here in Florida.

The following photo is a green roof succulent just recently infected with a fungus commonly know as Southern Blight, or Sclerotium rolfsii.  June 2010, Florida.

Now, one month later and the following photo is a green roof succulent seriously infected and dying from Sclerotium rolfsii.  June 2010, Florida.

 Note how the small branch has fallen over.


The good news is Southern Blight, or Sclerotium rolfsii is not usually spread by spores, rather through soil.  You must be selective about the source of all your green roof plants to prevent your green or vegetated roof from becoming infected with Sclerotium rolfsii.

And you must be selective about the soil mixtures you use!  Regular nursery soil is at risk to have Southern Blight, or Sclerotium rolfsii spores in the soil, as the fungus is very common.  I find the spelling - ScleROTium appropriate.

Though not commonly transmitted by falling leaves from surrounding trees, if there is any Sclerotium rolfsii - even trace numbers of spores in the green roof soil, then the fallen leaves will provide a food source for the fungus and soon you will have a full blown infestation.

Succulents and sedums, along with many landscape plants and vegetables are susceptible to Sclerotium rolfsii infections.  The presence of the fungus is usually a death sentence for sedums.

When you witness massive sedum dieback across the southeastern US and especially in Florida, the reason for the dieback is usually an active Sclerotium rolfsii problem.

Because most green roofs use typical nursery soil, or soil imported on nursery plants, the fungus has become a common green roof issue.   Many people do not recognize the Sclerotium rolfsii and just assume sedums and some succulents cannot survive the torrid Florida humidity.

So what should you do about Sclerotium rolfsii?  How do you keep it off your vegetated roof?

Numero uno rule - don't use common nursery plants - most all have the fungus spores laying dormant or active in the potted soil.

Secondly, there is another fungus that feeds on the mycelium of Sclerotium rolfsii.  Some species of the genus Trichoderma eat Sclerotium rolfsii's mycelium - immobilizing the southern blight.

Finally use those companion plants who produce trace sulfur compounds - there are many.  Sulfur lowers the pH and helps keep pest insects and spore transmitters, at bay.

We are about to release an all natural Southern Blight fighting, Trichoderma attracting green roof soil amendment.  Check back frequently for details or email me.

So plant and enjoy your green roof Sedums - but follow the guidelines!  Hopefully you can keep the southern blight at bay.  

Happy Green Roofing!

Kevin