Wednesday, December 1, 2010

Florida Green Roofs...Cold Weather Impacts on Florida Extensive Green Roof Plants

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Here in Jacksonville we are supposed to experience our first frost-freeze of the year tonight - so I am posting a previous post about green roof plants in Florida and frosts. Enjoy and Happy Green Roofing!

The past week, January 5th through January 12th, 2010 has been one of the coldest weeks on record here in Jacksonville, Florida.  Hard freeze warnings have been issued every day.  Temperatures have dipped into the mid to upper teens many nights - - I even had an outside water line burst - my main supply line.

So how did the green roofs fare?  As expected, some of the plants weathered the cold just fine while others sustained slight to severe damage.

In addition to the freeze damage to the leaves and tender stem parts, there appears to be frost damage - due to epiphytic bacteria growth of Pseudomonas bacteria, a gram negative bacteria that also acts as an ice nucelator. From the available literature it seems that the presence of ice-positive Pseudomonas can actually cause ice/frost to form on the plant surface. Frost damages the epithelial layer, in many instances killing the plant.  See the Monday, December 22, 2008 blog about Pseudomonas and green roofs by clicking here.

The plants sustaining the most damage were the Sedums and Aptenias.  Aptenia cordifolia, a South African native is one of the most reliable spring, summer and fall plants for Green Roofs in Florida.  Between the freeze and the Pseudomonas the plants have repeatedly died over the past years on our trials.  A wonderful, thick and glossy low grower, Aptenia shrivels and turns brown in the severe cold, the stems separating from the roots.  I have not seen Aptenia reappear during the spring fresh growth spurts as I have with other species - especially the cacti.

So our data gathering continues and our knowledge of what works and what does not work in Florida's unique environment, grows with time and experience.

One of the surprising victims of the cold were many of the Sedums.  Sedum pachyphytumappears to have sustained significant freeze damage to the leaf structure.  I'll report back on what happens over the next couple weeks.

Happy Green Roofing!

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