Green Roof Soil - What Kind of Soil Should I use in my Green Roof?

Choosing the right type of soil for your green roof project is very important.

Recently we talked about using a sterile soil mixture.  Non-sterile soils can bring in unwanted fungi and diseases and can damage or kill your installed green roof plants.


Today I want to discuss another green roof soil issue - water retention characteristics.  Again, realize we are coming from a non-irrigated, extensive Southeastern US perspective, and what works here in the long, hot summers and relatively cold but short winters may not work for your locale.  We believe in information sharing and encourage others to do the same so Green Roofs can proliferate successfully around the world!

Our practical experience has shown green roof plants do not like wet feet.  Dampness encourages disease and fungal growth.  Recently, an rather large Orlando green roof project was redone by the installer due to one of the components being installed upside down to where water was retained rather than drained away.

So your green roof soil should drain water away from the plant rather than hold moisture around the roots.

Many green roof plants acclimate to nature's background rainfall patterns and will quickly drink and store moisture from dew, humidity and rainfall.

However they usually do not like having their roots soaking in water.

I was reading about several efforts in Australia - from Green Roof's Australia newsletter - about how research is being conducted on green roofs and water - lot's of good information on Wilson Kath's blog.

Additionally, ASTM has several standards for green roof soils and drainage, including ASTM E2399 and others.

It goes without saying that your green roof system must be designed to accommodate the drainage properties of your green roof soil.  Small containers without drainage will result in pooling and plant health issues.  Large trays or open floors/mats should help with the facilitation of draining water.

A quick google search of "green roof soils" pulls up many good engineered soil vendors.  Moreover, many universities, such as University of Central Florida and others are researching green roof soils and obtaining patents for such.

Ultimately, the type of green roof soil will depend upon many factors - sun exposure, wind exposure, depth of green roof system, desired plants, climate and more.

The important maxim to remember is - generally you want your green roof soil to drain well.

Good luck and happy green roofing!  As always - you may email me with your questions.

Kevin

Sedums on a Green Roof or Living Walls? Should I use Sedums in Florida

Today I am going to take a leap of faith here, stretch out my neck and say "Yes - Plant Sedums and Succulents on your Florida Green Roof!"  However there are several important qualifiers to this statement.

First of all - let me show you what will most likely happen once you plant a succulent or sedum on most of the vegetated roofs I've seen here in Florida.

The following photo is a green roof succulent just recently infected with a fungus commonly know as Southern Blight, or Sclerotium rolfsii.  June 2010, Florida.

Now, one month later and the following photo is a green roof succulent seriously infected and dying from Sclerotium rolfsii.  June 2010, Florida.

 Note how the small branch has fallen over.


The good news is Southern Blight, or Sclerotium rolfsii is not usually spread by spores, rather through soil.  You must be selective about the source of all your green roof plants to prevent your green or vegetated roof from becoming infected with Sclerotium rolfsii.

And you must be selective about the soil mixtures you use!  Regular nursery soil is at risk to have Southern Blight, or Sclerotium rolfsii spores in the soil, as the fungus is very common.  I find the spelling - ScleROTium appropriate.

Though not commonly transmitted by falling leaves from surrounding trees, if there is any Sclerotium rolfsii - even trace numbers of spores in the green roof soil, then the fallen leaves will provide a food source for the fungus and soon you will have a full blown infestation.

Succulents and sedums, along with many landscape plants and vegetables are susceptible to Sclerotium rolfsii infections.  The presence of the fungus is usually a death sentence for sedums.

When you witness massive sedum dieback across the southeastern US and especially in Florida, the reason for the dieback is usually an active Sclerotium rolfsii problem.

Because most green roofs use typical nursery soil, or soil imported on nursery plants, the fungus has become a common green roof issue.   Many people do not recognize the Sclerotium rolfsii and just assume sedums and some succulents cannot survive the torrid Florida humidity.

So what should you do about Sclerotium rolfsii?  How do you keep it off your vegetated roof?

Numero uno rule - don't use common nursery plants - most all have the fungus spores laying dormant or active in the potted soil.

Secondly, there is another fungus that feeds on the mycelium of Sclerotium rolfsii.  Some species of the genus Trichoderma eat Sclerotium rolfsii's mycelium - immobilizing the southern blight.

Finally use those companion plants who produce trace sulfur compounds - there are many.  Sulfur lowers the pH and helps keep pest insects and spore transmitters, at bay.

We are about to release an all natural Southern Blight fighting, Trichoderma attracting green roof soil amendment.  Check back frequently for details or email me.

So plant and enjoy your green roof Sedums - but follow the guidelines!  Hopefully you can keep the southern blight at bay.  

Happy Green Roofing!

Kevin 

 

Install a Florida Green Roof and Save a Species From Extinction - Habitat and Green Roofs

Ever thought about helping save the planet's wildlife from extinction?  Installing a green roof or living wall can help.  Many species are dependent on the amount of greenery growing up above the ground for survival.

Species like the green Florida anole, Anolis carolinensis are being pushed towards extinction by newcomer lizard species to Florida, such as the Cuban anole, Anolis sagrei.  However, the Cuban anole prefers lower, bushy plants and tree trunk areas for habitat while the Florida green anole likes taller greenery and vegetation.

So by adding what we call 'Volumetric Green' to your urban yard, you are providing the Florida green anole with a place to escape predators and live.

Green roofs and living walls are the perfect way to add volumetric green to your commercial building site or to your residence.

We have seen over and over how the addition of a small green roof can help increase the population of the green anoles.  For a great website on this interesting species see the Discover Life website -   and for a great video of a green anole who loves riding wind turbines - click here.   

Installation of a green roof and living wall will not only offer the benefits of cleaning stormwater, providing habitat (saving a species) and creating beauty - when you install your MetroVerde green roof you are creating a permanent and effective method of Pest Control!  Anoles love to eat mosquitoes, termites and roaches!  Check out the you-tube video appropriately labeled "Crunch!"  

Specify and install a MetroVerde Green Roof today and help save a species!

Happy green roofing.

Kevin

3 Most Important Reasons to Build a Green Roof in Florida

There really are lots of good reasons to build a green roof in Florida and across the southeast United States.  The three reasons to build a vegetated roof here in Florida that I use most are:

Reason # 1 to build a green roof in Florida.

You will clean stormwater and help reduce runoff.  Our observations and data recordings have shown that on rainfall events of less that 0.50 inches ( 13 mm ) the plants and soil on the green roof capture and hold the rain - thus reducing the amount of stormwater runoff leaving a site.

Now all roofs reach a saturation point and will begin to discharge rainfall as runoff however since the majority of rainfall events we have here in Florida are less than 0.50 inches ( 13 mm ), then the green roof is capturing most of the rainfall.  This helps keep nutrients and other pollutants out of the stormdrain and out of the river.

Reason # 2 to build a green roof in Florida.

You build the green roof and the wildlife will come.  We have long seen that once a green roof was installed - wildlife, including green and brown anoles (lizards), tree frogs, lady bugs, butterflies, dragonflies, hummingbirds and other species visit the green roof in mass on a regular basis.

Research shows that many species are dependent of vertical green - or green up off and above the ground for survival - to escape predators.

The reemergence of native wildlife around your green roof will provide many benefits ecologically, not the least importance-wise is - an integrated pest management system.  You will notice a great decrease in fly, roach, termite and other pest populations as the lizards and tree frog population numbers grow.

Reason # 3 to build a green roof in Florida.

They are beautiful, provide oxygen to a hot city, take up and sequester carbon dioxide and give us humans a sense of place - a sense of belonging - in an otherwise hot urban concrete or asphalt setting.

So there you have it!  Three most important reasons to build a green roof in Florida.

Happy Green Roofing!
Kevin

Did your Green Roof Turn Out To Be Something You Didn't Expect?

Don't laugh just yet - I hear this comment often!  And its true, vegetated roofs have a mind of their own.  But today I am writing because I was meeting with one of the professors at one of the universities last week.  We were discussing a stormwater research project.  Near the end of the meeting the conversation turned to the many BMPs referred to in the proposed new Florida stormwater rule, one being Green Roofs.

The professor, with humor in his/her voice, spoke of the green roof project the university architect designed and how after installation the roof looked beautiful.

Continuing, the professor added that the roof had changed so much over the past year that most associated with the project were shocked.

I've seen this occur on every vegetated roof here in the Southeast US.  The maxim is:  Unless you have an endless budget for maintenance and unlimited time to work with the roof, expect change.

Through design you can minimize the change but you should still expect change.

The winds, rain and birds bring seed material.  New aggressive pioneer species pop up right and left.  The harsh environment knocks back the carefully tended to plants installed during the initial planting.  Harsh winds desiccate some of the plants.   Others wilt or develop dampening off with the high heat and humidity.  A vegetated roof generally has a mind of its own and you must ask if you have the time and energy to fight.

Again, I remind all I am speaking from a Florida and humid Southeastern US perspective.  Green roofs may behave different up north, I do not know.

So, I smile when I hear someone say, usually while shaking their head, that a vegetated roof has turned into something they did not expect.

We are compiling a database of plants suited for Southeastern US roofs and will be posting before the end of the year - would love your feedback.

Happy Green Roofing!

Kevin

Plants for Green Roofs - The new MetroVerde Carbon Pirate Variety

First off, even though we are a registered nursery in the State of Florida we do not generally sell green roof plants.  The plants here and the way they were raised are for our own green roof projects.  We are sharing the information of both our successes and failures in hopes we will someday have a greener world.  Our commitment is to restore volumetric green to the urban core.

We've mentioned before in the blog the practice of hardening off drought tolerant and succulent plants before installing them on green roofs, but today MetroVerde officially rolls out its Carbon Pirate (trademarked) line of green roof plants.

What is so special about the MetroVerde Carbon Pirate plant line is the time and preparation put into the plants in anticipation of roof duty.

Realize we focus on the Southeast US and especially Florida, so our approach may not be the best approach for other regional climates.  But here in Florida - green roofs face the big 5 H's, Heat, High Humidity, Hard Freezes, Hard Dessicating Winds, Hurricanes, Heavy Downpours, Hot Periods of Long Drought (Looks like 7 and I could add a Host more) - the point is that once you step up onto a Florida roof, no matter what time of the year, your breath can be taken away.  And you understand why you cannot just plant a nursery grown specimen on the roof.  May look good for a few months but after that - well just look at most of the previous attempts here across the state (except for a select few).

Drought tolerant plants possess specialized physiological processes that respond to changes in nature such as rainfall patterns and temperature.  They have developed these functions over the eons and rely on these adaptations for survival in areas where water supply is unpredictable.  Many have very shallow radial root architectural structure with diameters that exceed many times the plants actual form.  These roots want to grow laterally rather than downward in response to the infrequent rainfalls typical of their native habitat.  During a light rainfall event the stormwater tends to barely penetrate soil surface (depending on soil types).

As the rain ends and the water either evaporates or infiltrates, the drought tolerant plant broad surface area of roots responds quickly, storing the liquid for later use.

Additionally the drought tolerant have developed an array of mechanisms for dealing with drought such as CAM - or Crassulacean Acid Metabolism, and we will discuss these in upcoming posts, but lets get back to root structure.

For example, a two foot tall cholla plant often has a thirty foot architectural root diameter.  The fundamental distinction of any drought tolerant plant is the broad lateral root architecture.  Note the difference between some plants that do well in dry areas yet long, vertical systems that tap into the ground water supply.  Examples of these would include; Acacia, Parsley, Burdock, and Mesquite (whose roots have been know to grow down vertically over 200 feet!).

In choosing a green roof plant you first want to select one with roots that want to grow radially, not vertically.  But there are logistical limitations with plants that have radial root systems - they do not like pots or containers.  They need room for their roots to grow.

Recall the times you have gone to a nursery and purchased a plant and returned home to find the plant's roots had circled and circled the inside of the pot - we call this being 'root bound'.  Not good for the plant.

However, practically speaking nurseries are not going to grow one plant in a large tray because of the economics of space, real estate and cost-effective efficiency (I couldn't afford to either).

Hence the dilemma.  A drought tolerant plant grown in a two inch deep container that is three inches by three inches wide will not survive over term on a green roof.  The available functioning root area will only be approximately four and one half cubic inches.  Now as long as the plant is in the green house with irrigation applied (strange to think of applying irrigation to a drought tolerant plants) the plant will probably survive.   However, if raised in a small pot and irrigated, the green roof plant when planted on a roof most likely won't make it.

Drought tolerant plants for the most part have water intake processes that work gradually.  They are used to taking in required water volumes at a lower rate per root surface area using a large root diameter rather than absorbing large volumes of water with a limited root surface area.

The change from greenhouse container with irrigation to the roof is usually just too much and the plants will not function as expected without intense maintenance, watering and fertilization.

Though a topic for another blog session, my firm belief is because here in Florida we have a severe water crisis and nutrient pollution crisis, designing a green roof with irrigation is a fundamentally not environmentally sound.  I know, the cistern argument - hold the rainwater and irrigate with rainwater, but anyone with a cistern in Florida will tell you it is empty most of the time and then you have to use potable makeup water.....  I'll reiterate - my firm belief is because here in Florida we have a severe water crisis and nutrient pollution crisis, designing a green roof with irrigation is a fundamentally not environmentally sound.

Working with some of our green roof species we've 'trained' (this almost sounds cruel) certain plants to bridge the gap between being raised in containers and roof plantings.  Using drought tolerant plants (we will discuss in future blogs) - and let me note here there is a difference between drought tolerant plants and the succulents and cacti - we are not referring here now to succulents or cacti - using drought tolerant plants grown in standard nursery containers, we apply restricted watering schedules over a long period of time - usually over a year, to harden off the plants and prepare them for roof service.

These plants are grown in hot greenhouses with background humidity levels and irrigation amounts of less than 1/2 inch per month.

Once installed on a green roof with a mat based foundation, their roots quickly grow out laterally and with cumulative input from humidity and natural rainfall, they survive and begin to fill in the roof area.  In contrast to the irrigated, happy plants that are fatally shocked once installed on a roof, these plants are relieved to find their home on a roof.  We call these plants MetroVerde Carbon Pirates (trademarked).  They sequester C through respiration, produce oxygen, clean stormwater, provide habitat and create a much need sense of place.

There is so much to talk about here - tray systems versus mat  based systems, whether or not to irrigate, cost, weight, fire hazards, maintenance, volunteer species, disease - but we have plenty of more blog discussions coming!  In the meantime happy green roofing and as always you can e-mail Kevin with your questions - kevin@metroverde.com.

Allium - MV's Bonsai-ed Variety - Green Roof Plants Florida

I'm sold on Allium species for both green roof and living wall plants.  Hardy, evergreen, tolerant of inundation and tolerant of drought, these hardy plants form the backbone of many non-irrigated green roofs.  MetroVerde's bonsai-ed variety is an especially hardy variety - grown in a greenhouse with limited watering - typically les than 1/4 inch per month for over a year.  This picture I took today at University of Florida - we have a panel there - as we've written about before - and the system is non-irrigated, been in a harsh test area for over a year now - and the Allium species are growing strong!  Call Kevin with your low weight, extensive, non-irrigated green roof questions. 904-294-2656.

Another Green Roof in Hot Florida with No Irrigation - Green Roofs for Florida

This a small green roof we did in 2008 at Rob Overly's house in Jacksonville.  It is small (4' x 4') but in a very hot, harsh spot with on shade.

Rob, being the sustainable architect with a flair for clean water - being the water guru for Rotary International and traveling the globe on a mission of Sustainability - approached me and asked if we could do a pilot green roof on his front porch.  Using TPO over shingles and our mat and soil we planted the green roof using garlic chives, yuccas and bulbines.   Much to my surprise - two years later, the bulbines are the survivor champs.  Now birds, pollinators, tree frogs and anoles use the green.

I would have thought the winter cold would have killed them.  I would have guessed the garlic chives would be the surviving species.  However since this was to be a prelude to inexpensive technology in rural mother earth, one of the design criteria was a engineered soil layer of 3/4 inches of less.  This is probably why the garlic chives did not survive.  The TPO serves as the root barrier, and doing an excellent job at keeping roots out of the shingles.

This is an non-irrigated green roof that has survived temps ranges of 10 degrees F to  150 degrees F (measured on leaf surfaces with ExTech InfraRed).  Periods of no rain up 9 weeks and periods of intense inundation.

One of the reasons the section of roof shown was chosen is because it receives runoff from a long valley on the above roof and during a serious rain event there is a flood coming across the vegetation.

Call us with your green roof requirements.

Soilless Living Wall - Hydroponic Living Wall

Check out the MetroVerde living wall being installed into an historic downtown Jacksonville, Florida building presently being renovated into an upscale Indie Thai restaurant.


Pictured here are the wall panels during the plant establishment stage.

Call Kevin for your vertical green requirements - interior or exterior.  Cleaning stormwater, providing habitat and creating a sense of place!

What Plants Should I Use For My Green Roof?

What plants should I use on my green roof?  I hear this question often.  The answer depends on your site orientation, sun exposure, rainfall amount, location, temperature zone, exposure and a host of other variables.

However I strongly suggest you take a tour around town as a first step in selecting green roof plants.  You will be surprised at what you find.  Look up at the top of buildings, old churches, in roof gutters - especially in older downtown areas.

Some of the most successful low maintenance, extensive and non-irrigated (other than natural rainfall) green roofs have been those pioneer and volunteer native plant species established and growing in gutters and along roof parapets.

If you are serious about understanding green roofs you will take the time to go, look, find, and identify the plant species growing without any additional assistance on the roof of your downtown buildings.

Though these plants may not ultimately be those you use, they will provide a solid understanding of the plant morphology and structure that does well under the influence of the 5 H’s.