Rain, Green Roofs in Florida and Climate Change Issues

Drought everywhere!  Jacksonville received only a small amount, way less than a tenth of an inch of rainfall last night.

MetroVerde Florida Green Roof, Breaking Ground

Here in Jacksonville we've had little if any rainfall for weeks now.  The saying spring showers brings May flowers does not hold true for the geographic climate here.  As weather fronts push down and across the US they loose momentum and dissipate just before reaching Jacksonville.  All the dry weather is rough on green roof plants.

However, being situated on the Atlantic Ocean we are constantly exposed to high winds.  When the weather fronts come through they drop all their moisture west of Jacksonville typically but retain enough wind turbulence to stress unprotected green roof plants.

Over the past year on the Breaking Ground Green Roof I have watched in amazement at the amount of water the dry winds were stealing from the plants as breezes whipped across the flat roof at 4 or 5 meters per second.  Are we seeing the results of climate change or is this an expected cycle?

Of course the CAM plants were fine and this is why we suggest planting a belt of CAM plants around unprotected green roof perimeters.  CAM plants generally keep their stomata closed during the day.

C4 plants like the Poaceae hold their own, as long as they are established.  The corn, lemon grass and native grasses don't seem to mind the desiccating winds though I am sure after time they too would suffer without some rainfall.  I love the wave action native grasses produce in the wind.

The Asteraceae too do well, again as long as they are established and again, most are considered C4 photosynthesis possessing plants.

But the C3 plants can dry out so quickly.

Because we are doing an install I water the plants to help them settle into their new home.

Typically, wind is so drying and strong I can hold the hose to where the stream of water was flowing vertically up and evaporating or being stolen by the wind before the droplets could ever make it back down to the plants.

Watching the C3 plant leaves move in the wind I could see the same occurrence happening, water being quickly vaporized out of the leaves just as the droplets from the hose where also 'gone with the wind'.

Sitting there with the hose I witnessed some of the more tender vegetables quickly wilt even with the hose  water directed at their roots.  The plants vascular system could not keep up with the wind induced evaporation of leaf moisture.

Without water in the leaves plants can not conduct photosynthesis.  Without photosynthesis plants die,

Wind impacts are so significant across green roofs.

In MetroVerde's opinion wind exposure is, with light, availability the most important consideration for green roof design.

We've posted numerous articles here on how to use CAM plants as wind breaks.  Understanding wind impacts on green roofs is critical for long term green roof design success.

Best Plants for Florida Green Roofs? There are many says MetroVerde!

Best Florida Green Roof Plant?

Metroverde is always working to find suitable plants for Green Roofs in Florida.  For years Northeast Florida has been experiencing a severe drought.  Finding the toughest and most visually appealing is only part of the process.  Habitat value, invasiveness, wind and drought tolerance are other issues we consider.

Green roofs in Florida are harsh places – remember the 7 (or more) H’s:

1. High Humidity
2. Hot, hot heat
3. High desiccating winds (killer)
4. Hurricanes (not the football team)
5. Hard Freezes
6. Horrible temperature swings
7. Hurtful droughts
8. Harmful floods

And we all are cautious about irrigating a green roof (I speak as a lawyer – not a botanist here) – our litigious society has already bred a number of legal articles on green building and tort.  Imagine – the issues of:

• Mold
• Water damage to interiors
• Collapse from weight (water is heavy)
• Bacterial breeding
• and who knows what else…

So if we choose to acknowledge Florida’s water shortage problem and build a green roof with micro-irrigation or no irrigation at all, then we need to look to plants that:

1. Can survive the many H’s
2. Are visually acceptable by the community
3. May be cost-effective
4. Are preferably native species (or non-invasive species)
5. Do not present a fire hazard or contribute too much dry leaf litter
6. Are low maintenance
7. Can survive long periods of drought
8. Can survive twenty inch downpours
9. Resist fungal infestations
10. and much more

Two of the most outstanding plants that almost begin to come close to the above requirements are:
1. Frog Fruit (Lippia nodiflora), and
2. Wild Garlic (Allium canadense)
I’ll be posting more data on these two species over the next couple days.  In the meantime – what are your experiences with these species on green roofs?

Green Roof Plant Dwarfed 2 Year Old Allium Canadense

Florida Green Roofs and Wind Impacts on Green Roof Plants

Wind is an oft-neglected but so important design parameter of green roof layout.

Dry, desiccating winds can damage or kill green roof plants faster then drought or a host of other environmental factors.

Included here are two photos of the same black-eye pea plants.  One is on a wind protected green roof, the other is on a wind exposed green roof.  Note the wind burn on the wind exposed roof plants.

Both looked the same prior to the 48 hour wind storm just leaving.

MetroVerde  recorded between 10 and 20 Km/Hr winds on a continual basis for the 48 hours with almost non-existent water vapor or air humidity.

Florida Green Roof, Wind Protected Green Roof Plants

Florida Green Roof, Wind Exposed Green Roof Plants

Wind can burn or kill green roof plants quickly, taking an otherwise beautiful planting and turning into a brown mess within a matter of days.  Even with more than adequate irrigation water applied - simply because the vascular system of the plants cannot keep up with the demand for water in the leaves.

CAM plants and those plants with stomata remaining closed or closing under lack of water conditions must be used as perimeter wind break plants on green roofs with out parapets or other wind protection if the green roof is not otherwise sheltered.

Understand the different types of photosynthesis green roof plants have.  For a primer, check out the many articles we have posted before on CAM, C4 and C3 plants.

Other helpful sites are included here;

Great Irish Gardening blog article on wind damage in Ireland to garden plants.

North Carolina State University has another brief yet informative note on wind desiccation of plants.

Very interesting and informative Permaculture Wind Break Site.

Remember, your green roof site may receive plenty or precipitation or irrigation water, but if it is constantly exposed to desiccating winds the plants will experience the effects of wind damage.

Florida Green Roofs and a Terrible Drought! Looking to Poaceae

Here in Northeast Florida we continue to suffer from extreme drought.  Strange, because four hundred miles west lies the city of Pensacola with an abundance of rain.  But here in Jacksonville, a harsh, dry, period of time marked with a significant lack of water is stressing and killing plants and contributing to wildfires.

Selecting those native plant species adapted to drought survival is important for green roof designers.

Poaceae is a good place to start.

Poaceae is the family of grasses, referred to previously as Graminaceae.  According to Wikipedia, Poaceae contains about 600 genera and around 10,000 species of grasses.

Grasses comprise from 20-25% of all the herbaceous vegetation covering the earth.

Wikipedia, as other sources also suggest the Poaceae is the single most economically important family of plants in the world to humans, containing many food, grain and cereal crops, such as corn, rice, wheat and barley.

Poaceae grasses contain both C3 grasses and C4 grasses, referring to the much discussed in this blog 'photosynthesis process' type.  The above link also contains a list of commonly known C4 plants.

C4 plants have evolved a process to survive drought.  They protect compounds in their leaves, crucial to photosynthesis, from dessiccation and loss through a variety of means, including; timed stomata openings, storage of photosynthesis compounds in vacuoles and separation of photosynthesis reactions into differentiated cells.

This means they can make an excellent green roof plant or rooftop garden species.

As does corn.

Corn growing on Rooftop Garden, Sudan, photo by S. Newman

Sudan is dry.  Corn, Periwinkle and Mango thrive. Photo by S. Newman.

As you can see from the above photos, Sudan is a dry and arid place, hostile to most plants.

However corn, a Poaceae family member thrives on a hot, dry, windy roof.

MetroVerde also grows corn on roofs, and the plants will grow well in places most others would wilt in a matter of days.

Other grasses too, members of the Poaceae family adapted to drought make excellent green roof plants.  many are perennial and evergreen species, affording year in and year out color and texture, supporting biodiversity with food and communal shelter, providing beauty, cleaning stormwater and reducing heat island effect.

Purple muhly grass, Muhlenbergia capillaris, is another of my favorite green roof Poaceae.

Green Roof Muhly Grass, photo by C. Burkee.

Purple muhly gras, excellent C4 green roof grass.

There are many other grasses available and suitable for green roofs.  Preferring to use native species, I consult with local nurseries in an area to see what they recommend for drought tolerance.

Your local native plant society is also a good resource for grasses recommendations.

The beauty of the Poaceae family is that they have been around a long time on this earth and survive in the most inhospitable of places.

Try Poaceae on your next green roof!

Green Roofs, Deciduous, Dormancy and the Color Brown

Though not my favorite time of the year Winter always brings the welcomed sigh of relief to her pallet of colors with the appearance of a special deep brown.   Anticipating next year's vigorous renewal,  brown adds the fourth dimensional depth of time to the remaining sprays of green.

MetroVerde Green Roof Panel

Winter on the green roof is no different.  In fact, winter on the green roof allows for a period of correction, recollection and hope.

Of course Winter here in Florida is mild compared to what others across the world experience with respect to duration, we still get cold enough here to induce dormancy and deciduous characteristics in   many plant species (If you call a low seasonal temperature of the mid-20's F or - 6.5C cold).

Aptenia on a MetroVerde green roof

While it is always good to look out across a living roof and see vast expanses of green, deciduous brown can be reassuring.

Without the annual browning of the fast growing C3 plants the living roof would become a jungle, restricted in biomass output only by available water supply.  However after the first hard freeze, dead biomass can be removed from the living roof to expose C4 and CAM plant type successes, successes to be built upon for subsequent years design and growth planning.

C3 and CAM plants across a sloped green roof in Florida

For living roofs in dry and arid climates experiencing sub-freeeaing winter temperatures, winter visualness can be designed to allow for striking contrast of textures and colors.

Catherine Burkee, Educational Director for Breaking Ground Contracting here in Jacksonville has a wonderful video and note of the Breaking Ground Green Roof she recently posted about the changes of seasons as seen on their living roof.

I am looking forward to a great 2012 for living roofs around the world!