Blue Spruce Sedum on a Green Roof, Gainesville, Florida
In Florida, most do not do well. There are a few advantages sedum brings to a green roof, including;
- Extreme drought tolerance once established
- Unique color and texture
- Spread via rhizome and stem rooting, and others
There is an interesting discussion of sedum and biodiversity support found on the LivingRoofs.org website, where they encourage mixing sedum with wildflowers. The article does state sedum may have value to bees during the early summer months.
Yet as mentioned in the blog article, Sedums for Florida Green Roofs sedum can have a difficult time in Florida - especially because of Southern Blight and other fungal diseases.
Some say Florida's issues with sedum stem from high heat and humidity. However this is only partly true. High heat and humidity provide a platform for the real sedum killer, Southern Blight Fungus.
Southern Blight is transmitted primarily by spores in contaminated nursery soil or plants and becomes a rampant problem during Florida's long, hot, humid summers.
Though a sterile soil mixture may be used on a green roof, the fungus may still develop across the roof via means of birds carrying debris or vegetated material from the ground below. It is practically impossible to keep Southern Blight at bay once the hot, humid summer months arrive.
But if you are intent on trying sedums on a Florida Green Roof...try the Blue Spruce variety.
Sedum reflexum - Blue Spruce Sedum is one of the toughest I've seen, growing in Florida. S. reflexum can grow in the poorest nutrient containing well drained soil.
I've seen it on non-irrigated roofs in Gainesville - and last through brutal summers of hot sun exposure. Sedum possesses C4 photosynthesis processes, keeping the stomata closed during most of the day to avoid desiccation and evaporation of water crucial to the Calvin Cycle. Moreover, sedum possess specialized internal vacuoles to slow down water loss when temperatures soar and the sun shines.
I've seen it thrive in well-drained soils even during the wet season.
The downside to this plant is on hot, harsh roofs it is very slow growing and produces almost no root system, making it a candidate for easy blow-off during high winds.
So it won't spread quickly and fill in your green roof here in Florida.
But it should survive the 7 H's of Florida's Green Roofing Ecology and provide a small area of interesting color and texture.
Happy Green Roofing, Kevin