|Sedum devoured by Southern Blight Fungus|
The question was focused on Sedum and vernalization.
Below is my response.
I am certainly the wrong person to ask about success with sedum. I have tried for years in Florida with zero success.
We now believe the humidity, combined with other environmental factors such as fungi create such hostility towards the plant that she will not grow reliably on roofs here.
Most people in the green roof industry I speak with say they will not try and use sedum below a certain latitude - they typically say that when you are coming south and see the dominant tree canopy change from hardwoods to pine trees.
The sedum I've had the most luck with is the 'Blue Spruce' variety, Sedum reflexum. Yet this variety of sedum does not thrive and simply 'hangs on' longer than most other varieties.
Because sedum is propagated primarily by cuttings and rootings vernalization is not a survival issue here, in my horticultural opinion. I see many plants, such as Bradford pear, Pyrus calelryana, for instance grow quite well here - they simply do not flower.
There are two primary suspects, in my opinion that afflict sedum here and prevent the plant from surviving year after year on the roof. They are:
1. Sclerotium rolfsii aka Southern Blight Fungus (see a post about Southern Blight here), and
2. Pseudomonas bacteria (another post re Pseudomonas here)
There are many other plants such as Aptenia, Delosperma and others that respond the same way.
One way to avoid the fungus and bacteria is to use sterile soil. But as soon as a bird drops or wind blows debris onto the roof the Sclerotium establishes residency.
So rather than continue to battle trying to use this non-native plant on roofs here, I find better use of native plants and wildflowers who the local pollinators and wildlife value much more highly than the sedum.
I am sure someday GMO technology will create a super sedum for Florida.
Sometimes information on what hasn't worked is just as important for Green Roof technology as are success stories.
Hope this helps!