The first test strip is a month old! The month of August was gentler than usual in South Florida, many days were around 70, with a few scorchers on the roof at 120 degrees. We had over 12" of rain. Not a bad month for a test strip and it is thriving. The drip system is in place for use during drought periods.
South Florida Water Management and DEP are among jurisdictional agencies meeting in Orlando today to develop new laws regarding sustainable solutions for storm water management including practices encouraged by Low Impact Development. Low Impact Development includes stormwater and land development strategies that emphasize conservation and use of on-site natural features integrated with, small scale hydrologic controls in an effort to mimic predevelopment hydrologic conditions. Practices include minimizing impervious area and compaction, rainwater harvesting, permeable surfaces, depression storage, bio retention, soil filtration, vegetated swales, enhanced stormwater ponds and green roofs. Retain, Detain, Recharge, Filter and Use!
On August 8th we planted the first of what we hope will be a series of test strips experimenting with different recipes to determine the best plants, planting media, planting methods and maintenance activities for green roofs in South Florida. 
We are not testing the layering system, waterproofing etc. We are using the easiest construction methods and least expensive materials for the trays and layering system because of budget constraints. The trays are made of pressure treated pine. (cost not weight consideration) The tray is lined with pond liner. A layer of “cups” approximately 2" deep are laid out on the pond liner to mimic commercial drainage systems that get water out of the planting media yet store it for future use. We made this layer out of recycled soda cups. This layer is protected by a filter fabric. The planting media goes on top of this.
The layering system loosely resembles what has been developed by others, commercial green roof providers and the system designed by John Szerdi at the Eco-Centre in Lake Worth.
We are planning to start with two test strips and would like to add more as time and money allow. Only one has been installed so far.
These are the parameters of the test:
Two trays 30” x 30”
One tray will have a 3” planting media depth.
One tray will have an 8” planting media depth
We will plant a mixture of plants in both trays
The 3” tray will have spreading ground covers: Bulbine, Mimosa Strigulosa, Perennial Peanut
The 8” tray will have a mixture of grasses: Wiregrass, Equisetum, Muhlie Grass
Some wildflower seeds will be mixed in with the grasses, just to see what happens: Greeneyes, Gallardia, Coreopsis. These were recommended by the Florida Wildflower Coop.
Both trays will have the same planting media:
50% black lava rock mixed with 50% Canadian peat topped with 1” shredded eucalyptus mulch.
We will ensure that the strips get water, at a minimum, once every three days through an establishment period of one month. After that month, the strips will only be watered if there is less than 1” of rain over a period of 10 days.
We will take pictures of the plants once a month and post them on the blog.
After three years, we will pull the plants to examine their root mass.
These are our assumptions:
Soil mix: We wanted to develop a mix that would be light, drain well and have a little bit of organic material. The lighter colored mulch on top will keep the planting media cooler and retail some water. The black lava rock will have a better ph than red lava rock.
Plant choices were made from our experiences with plants in South Florida. We wanted to use plants that could take very wet or dry conditions in case the tray became flooded over a period of South Florida rainy days. We feel that a mixture of plants is better than a mono culture. Our plant selections are not all native but are selected because we have found that they are very tough and adapt to wet or dry conditions.
We used “trays” for several reasons. We did not have a location to do a full out extensive green roof directly on the roof membrane. Many people feel that trays won’t work in South Florida because they’ll blow off in a hurricane. There are two ways that wind can be approached. The first is to make the “planters” weighty enough to resist hurricane force winds as John Szerdi did at the Eco-Centre. The second is to secure lighter trays to the roof securely enough to resist uplift. We developed one detail for this with Botkins and Parssi for a penthouse garden in Palm Beach and have some alternative attachments that we would like to test in the future. For this project we plan just to put the tray on the roof and remove them when necessary.
Another reason I wanted to experiment with trays is because I’m concerned about what will happen when plant roots make an extensive roof “root bound” over a period of time. Since plants don’t go dormant in South Florida, will the roots take over within 5-10 years? Would the whole roof have to be replanted over a period of time? Or would it be easier to switch trays out? Or, are there plants that wouldn’t develop much of a root system and still survive?
This is our hypothesis:
The plants we have picked are survivors.
After three years, the roots the tray will be ‘root bound’ to a point that it would jeopardize plant health in the following year. The implication of this would be that it would be best to use trays that can be switched out or a plan to replant the roof after 3-4 years.
Potential future test strips:
Dune plants – will they be able to take inundation of several rainy days?
Lighter colored lava rock no mulch – determine weight savings, does ph matter?
Mono cultures (all one type of plant)
Parallel trays that aren’t disassembled after 3 years to see how much longer the plants survive.
Do you have any other ideas?
Please let us know what you think of our assumptions and the way we have set the test up.
Sprout!
If you go to one of the excellent classes provided by Green Roof for Healthy Cities, a point that is emphasized is that green roof plants are planted in planting media and not soil or dirt. Why? Most green roof applications are concerned about water retention and weight. Organic matter has a tendency to hold onto water and weigh more, depending on its actual composition. Therefore it is of greatest importance that the planting media is carefully thought out, specified and installed.
The factors that affect media selection are climate, weight, fertility, depth, location, microclimate and irrigation or lack of it.
The products used are typically a mixture of organic and inorganic matter with significantly more inorganic matter in extensive systems. Inorganic matter used includes vermiculite, expanded slate, expanded clay, lava rock, coarse sands, pumice stone, zeolite, diatomaceous earth, perlite and rock wool.
Planting media is critical to long term plant survival, stormwater retention and heat mass transfer. The composition of the media determines the system’s saturated weight, evaporation, drainage capacity and compactability. Plants need water, air and space for roots and nutrients. How well these needs are addressed depends on the planting media.
An area of controversy within the industry is how much organic vs. inorganic material should be in the planting media. The Winter 2008 Issue of Living Architecture Monitor addressed this issue. The inorganic supporter, Chuck Friedrich defines planting media as the particulate matter or substrate that anchors plant roots to sustain plant growth. His recommended mix is:
He gives the following plugs for inorganic planting media:
Inorganic materials provide good drainage
Inorganic materials do not change over time like organic matter does. Organic matter can break down and wash away. Replacement of organic material can be labor intensive. Organic material may produce fine particles which clog filter fabric.
Inorganic media ensures that enough air can be provided to encourage roots to go down instead of up because of oversaturation. If roots are down, the plant can sustain itself during periods of extreme temperature.
He instructs NOT to mix fertilizer into the planting media but to apply it directly to the plants after planting. He also recommends the availability of irrigation for droughts.
The Organic supporter, Rick Buist, bases his support for organic media on over 80 successful installations using organic based planting medias. He feels that the push for non organic planting media stems from proprietary blends. However, the “Organic based planting medias” used in the 80 successful installations are not defined, so it is difficult to tell the degree of difference between Rick and Chuck’s arguments.
Many current practices regarding planting media rely on a set of standards developed by a not for profit group in Germany, Forschungsgesellschaft Landschaftsenwicklung Landsschaftsbau. It seems that there is also confusion regarding what organic material is and how to measure it from Rick’s review of the FLL standards. Differences can occur if one considers the standards for mass or volume of organic material. Furthermore, the standard focuses on material specifications rather than performance specifications, which doesn’t allow room for specific applications or creative solutions.
Chuck does make some good points for organics in the following excerpts:
“The performance which organic matter brings to stormwater retention, pollutant degradation, plant variety, cooling benefits, sustainable materials, etc. is too great to ignore.
“Organic-based growing media can hold far more water than mineral based growing mediums while maintaining porosity: this is because of the way in which they hold water through particles swelling instead of just void filling and capillary forces. Biology can be customized to degrade specific and non-specific pollutants. Plants that provide evaporative cooling can be used more frequently with success. Fertilization can occur naturally through nutrient cycling. Materials can be sourced locally.”
“Practically every argument I have heard against the use of organics comes with a relatively easy solution:
Lost depth because of organic cycling is easily addressed through inputs such as biomass created by the plant choice through roots or refuse or annual (if required at all) top-dressing with a pelletized product such as compost or alfalfa (readily available in a dry, bagged form)
Fines clogging drains or water logging can be averted by careful selection of organic materials. Organics with crystalline structures such as certain bark-based products will behave much like sand for free drainage while organics with strand characteristics will hold structure together. Careful selection and installation of components such as filter cloth are also helpful.
Wind erosion is averted by using biodegradable netting until plants are established, thereby providing continuous cover.
Fire prevention can be improved by avoiding certain substances (i.e. peat moss – a limited resource) and by using organics with a high ignition-thresholds and large moisture-retention capacities. Although any biomass on a roof can burn, it is easy to mitigate the risk by paying attention to the details.”
Source: The Organic Question, Living Architecture Monitor, Winter 2008 Volume 10, No.1.
How can we apply these observations into a planting mix? Please share any thoughts, recommendations or experiences.
The following is a summary of some of our observations on planting media thus far. These observations will be incorporated into green roof planting tests to determine the best design approaches.
Use a minimum of 6-8” of planting media for grasses. If the particular situation can only accommodate less than 6” of planting media, only use the toughest of the tough spreading ground covers.
Peat moss has a spongy structure that provides a high nutrient, water and air holding capacity. It is a light organic material that will retain 20% of its weight in moisture and will reduce the need for additional water. Peat moss is sterile and therefore free of weed seeds and pathogens.
Unfortunately, peat is a non renewable resource that is harvested from wetlands. Peat harvesting accelerates the decomposition process; the carbon that is stored in peat is released to the atmosphere as carbon dioxide. Thus, peat harvesting is being regulated and peat prices are increasing as supplies decrease. The University of Florida is currently researching an alternative to Canadian and Florida peat – Cowpeat. Results from seed germination and rooting showed that the alternative media formulated with cowpeat had little difference in the percentage of seed germination and the percentage of rooting compared to those formulated with either Canadian peat or Florida peat. The use of composted manure, such as cowpeat, appears to offer a viable alternative which reduces peat mining and will contribute to the well-being of Florida’s environment. Source: For Peat’s Sake, Qiansheng Li, Jianjun Chen, Juanita Popenoe and Lelan Parker; Ornamental Outlook, August 2008.
Lava rock is a sterile media with tiny holes that wick up water and release it slowly to plants. Lava rock is a good choice for weight considerations and drainage, but black lava rock can get very hot.
Red lava rock can create ph problems.
When mixed with peat, black lava rock will give the soil mix structure, hold the peat in place and provide pore space for aeration.
Sand can often be too heavy for installations on existing roofs.
This summary was compiled from our observations at the Nancy Foster Florida Keys Environmental Center green roof, discussions with Glen Acomb, professor at University of Florida and designer of the Charles R. Perry Construction Yard green roof at University of Florida and conversations with Atlas Peat and Soil, a local supplier. These observations are not meant to be all inclusive and are above and beyond base recommendations regarding layering etc. that can be researched on national green roof sites.
No this isn’t a typo, I’m writing about a green roof that has gone brown. The Roy-Fisher Team visited this roof at the Nancy Foster Florida Keys Environmental Center in early June. The Center is currently completing paperwork for a Silver LEED certification and the green roof is included in their LEED point calculations. The building is surrounded on ground level by a thriving native landscape on a drip irrigation system that educates the public on native plants for a LEED innovation point. Although the roof is currently brown, we take our hats off to this pioneering group that built the first green roof in south Florida for a LEED building under the harshest conditions that South Florida can dish out. The roof did survive harsh salt winds, extreme heat and a hurricane until it fell prey to severe drought conditions, staff reductions and other priorities.
Leigh Epsy, the Chief of Staff during construction gave us a very thorough tour. We hammered Leigh with questions: What benefits did she realize from the green roof? Were they seeing a reduction in energy costs? Was their roof irrigated? What was the planting media? How deep was their planting media? What kind of plants did they use? Who designed the green roof? Why did she think it was brown? Did they plan to replant it?
The Center does not have a means to monitor the energy savings realized because of the green roof. Since this is the first LEED registered building in the Keys, it would be difficult to pinpoint which energy savings came from some of the other building features separate from the green roof.
Leigh felt that the biggest benefit of the green roof was stormwater retention. She based the benefit from a visual, not quantifiable assessment. She also felt that the green roof was a great marketing tool for LEED; people notice it. Questions about the green roof become a segue into explaining the concept for the whole building and site.
The original design was done by Charles Beazley from Lafayette, Louisiana. We couldn’t get information on the planting media specification but a Center employee recalls that it was black lava rock. A section we found indicated a 4” planting media depth.
The originally specified plantings were not planted but were replaced with a non-native African marsh grass recommended by a local nursery and it thrived. Once it was discovered that the grass was not native, it was removed and replaced with Spartina Bakerrii and Sea oxeye daisy. A conscious decision was made NOT to irrigate the green roof.
This is what happened:
The green roof was installed with less planting media. The black lava rock got very hot.
Despite the harsh conditions, the green roof thrived at first and actually survived Hurricane Wilma. Leigh recalls that the spartina did much better than the sea oxeye daisy.
In the spring/winter of 2008, the Keys experienced a prolonged drought. At that time, the Center was understaffed due to government budget cuts and, sadly, an employee passed away. The green roof was not a priority; the plants died from lack of water.
There is a happy ending however. The local Master Gardeners have adopted the project and are testing different plant species on the roof including sea purslane and beach elder, two tough native plants that can take salt and heat. The plants are being watered through establishment. We hope that eventually a drip system for emergency situations will be considered. The RFA team plans to get updates from the Center and visit in 6 months to see if the roof is green again.
I am fascinated by green roofs because I think they have unlimited potential to look really cool (usually my first attraction) but also because green roofs have amazing benefits that help the world, in general, and South Florida, in particular. It’s a “no brainer” that here, where it is really hot, we could benefit from reduced air conditioning needs, protection for roof membranes from the blistering heat, reduction in urban heat islands and help with storm water management.
Green roofs have made a minimal foray into Florida, with a dismal effort in South Florida. To date, there is a green roof at University of Central Florida that was installed about three years ago. A comparison between an area of conventional roof and an area of green roof done by University of Central Florida’s Stormwater Management Academy was published in the February 2006 ASHRAE Journal. The research showed that the daytime temperature for the green roof was 39 degrees cooler than the conventional roof! The ‘conventional roof’ was highly reflective and the study was done before the plants were fully grown. The average energy use required to remove the additional heat gain from the conventional roof over the summer period that was monitored was approximately 700 Watt hours per day. If a darker roof and more fully grown green roof were compared the savings would have been even greater!
There is also a green roof at University of Florida, over unairconditioned space, and one in the Keys at Nancy Foster Nature Center. Recently, a green roof system that cleans grey water was installed at the Eco-Centre in Lake Worth, but it has not yet been planted.
To reap the many potential benefits, it is important to study specific South Florida conditions that are different from most of the nation. It gets really HOT down here in August and September. How much hotter does it get when you are 30’-40’ higher? Does the cooling effect of a green roof offset its cost? How quickly? It is really HUMID here – Sedums used on green roofs in the rest of the country just won’t work- they get fungus and melt. We have BIG STORMS here. One of the fears I hear over and over is, “Won’t that stuff blow off the roof?” We get a LOT OF RAIN in short periods of time. What size planters and what conveyances would work best to either hang on to that water, use it for another purpose or make sure it’s clean when it comes out? We have a LONG GROWING SEASON. What plants will work best in the long run, that won’t get root bound? Or, do we need to figure out a modular system that will withstand hurricane force winds and can be changed out as plants overgrow?
Each project will, of course, have different conditions and parameters that require different solutions. A baseline understanding of answers to these questions is imperative so that green roofs can succeed in giving the benefits that they have the potential to give.
A demonstration green roof could evaluate different methodologies and educate the public on the many benefits that green roofs could provide South Florida. Does anyone know of an agency contact that would be willing to sponsor or give a grant for these studies? South Florida Water Management? IFAS? FAU? Palm Beach Community College? Palm Beach Atlantic College? Florida Power and Light?
Meanwhile, Roy-Fisher Associates is setting off to tackle some of these questions. We began with a visit to the Nancy Foster Nature Center, the only installed green roof in South Florida. This green roof has the worst conditions South Florida can dish out. It is on the very tip of Key West- probably the hottest spot in South Florida. It is also on the ocean, exposed to salt winds and it survived Hurricane Wilma. An upcoming entry will talk about our visit. As other green roofs are planted, we will report on them.
We are also testing a light planting media and specific plants in trays on our roof. An upcoming entry will describe our research approach and methodology. We will be posting data and pictures of our progress . These are labeled as ‘green roof entry’ on the calendar if you would like to review our progress.
We also plan to review material presented in Living Architecture Monitor and compare/relate it to South Florida conditions. Your comments on these reviews will be greatly appreciated.
We invite our professional partners to become regular contributors to our green roof entries, supplementing our expertise on engineering, contracting, environmental and architectural methods to create a sustainable foundation for green roof culture.
Sprout!
As more and more natural landscape is erased, it becomes increasingly important to create landscapes that restore, invigorate and inspire. A new idea is often a combination of knowledge and a random event. Knowledge is a concept; the random event can be supplied by nature. A sensory experience combined with a concept often causes one to think or take action out of the ordinary.
Our challenge is to create settings that are structured, yet provide opportunities for randomness and discovery. An architect creates a built environment for people to act or interact. Our purpose adds the component of setting the stage for people to interact with nature. This can give inspiration for new ideas and reveal different perspectives.
This used to be my favorite poem; I thought it described how design/landscape architecture could be used to organize the world around it.
Anecdote of the Jar
I placed a jar in Tennessee,
And round it was, upon a hill.
It made the slovenly wilderness
Surround that hill.
The wilderness rose up to it,
And sprawled around, no longer wild.
The jar was round upon the ground
And tall and of a port in air.
It took dominion everywhere.
The jar was gray and bare.
It did not give of bird or bush,
Like nothing else in Tennessee.
Wallace Stevens
This poem talks about how a built form organizes and influences nature. Here’s a paradigm switch, a change of perspective. What if we turned the tables? Instead of a built form that organizes nature, nature is used to enliven our built forms. What if we worked with nature to bring more life into how we see, how we live, and what we do? This is what Sprout is about.
