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

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!

Irrigation and Green Roofs - Green Roofs for Florida

The green roof test panel shown here is one year old.  We are preparing the unit for hurricane wind tunnel testing.    The only irrigation the roof panel has had is rainfall, and survived a very dry winter and spring.  Green roofs present a different growing environment for plants than do the ground.  No matter how rocky or little soil there may be, the ground offers a consistently cooler place for roots to exist.  A three inch thick extensive roof soil layer can reach temperatures of 140 degrees F or higher while the ground temperature is significantly lower.  So for plants to survive on a non-irrigated green roof, they must be carefully chosen.

We are raising a new breed of plants in the greenhouse where they are exposed to growing conditions much like those to be experienced on a roof.  Heat and prolonged drought.  With trials well into a year now, the plants go through prolonged leaf impact, however when finally brought out and exposed to rain, the bloom and grow.  Importantly, we look at the potentially for flammability when using plants with dried leaf matter or leaf litter.

One interesting quality we are seeing more and more of is the ability for plants to absorb humidity here in Florida.  Fortunately, even when the temperatures are torrid, the air relatively humidity may be quite high.  Air humidity can make the difference between a plant dying and a plant surviving a long period of non-rainfall.

Finally, with water shortages here in Florida and watering restrictions in place by municipalities and water management districts, why would a green roof designer recommend irrigation?  It is because they do not understand the 'right plant, right place' concept.  We have been working on green roofs for many years and understand those plants that work and those that do not.


Call us to discuss your next green-roof project!  Kevin 904-294-2656

Florida Green Roof Plants Withstand the Hard Freeze of February 5th, 2009

Look at the spread in the temperature range. It was in the low twenties at 5:30 am this morning - now at noon the surface temperature of the trial asphalt shingle roof is 120 degrees F.

How do the plants survive?

The above pictures were taken this morning about 7:45 am.

The plants were frozen solid. But they've thawed and are enjoying the sunshine now!

Happy Green Roofing. Kevin.

The Stress of Cold - Frosts and Freezes - on Florida Green Roofs

Tonight was the coldest night of the year with freezing temperatures reaching all the way down into south central Florida. It is still in the low to mid twenties in Jacksonville at 5:33 am.

Green roof plants have taken the brunt of the cold - sitting up on a roof, dessicated by the never relenting north winds, unprotected and exposed.

These same plants must survive in the extreme temperatures and humidity levels of the summer also.

I will be posting pictures later this weekend. Some of the plants are bit back and scarred, some may have died - but others are doing OK.

My favorite - Allium species - is a testimony to successful green roof plants....it never fails.

Post your results here too!

Happy Green Roofing - Kevin.

Florida Green Roofs, Green Roof Plants and Freezing Temperatures

Just got back from Tampa again. I came across some native grasses along the way at a small nursery - and brought them back to Jacksonville. They are low profile grasses - nice green color and light, flowing texture - especially for Winter!

I have already placed them up on the roof.

The weather forecast is calling for temperatures to hit the teens to mid-twenties across North Florida - and into the twenties all the way down into south-central portions of the state.

Record temperatures are expected (record lows that is).

Of course, Judy and I covered our citrus and some of our tender landscape plants.

But the exciting part of the cold is to see just how 'hardy' plants are on the roof. Some of my green roofing plants took a hard hit two weeks ago. They didn't die, but sustained some scarring. Others made it through the cold just fine.

One of the more interesting observations I've seen this cold season is that you can have two identical plants on the roof but one plant has been installed earlier in the year and has had a chance to 'harden' off to the harsh reality of the garden roof, while the other freshly installed plant has not. Not surprisingly - the non-hardened off plant suffered much more damage than the plant installed in the late spring.

This tells me that there are ideal months to install green roofing plants. I'd suggest it is best to install cold-hardy plants during the cooler months and cold-affected plants during the pre-summer season (allow the roots to develop and grow into the engineered medium before the stressful weather hits.

I'll update the condition of the native grasses after tonight's hard freeze.

Happy Green Roofing!