Friday, November 25, 2011

Green Roof and Leaves, Cation Exchange and Anti-Allelopathy Issues for Design Consideration

I had a couple of comments yesterday about my post on Allelopathy and Green Roof design.  As we focused on the potential negative impacts adjacent trees and their sap drip, leaves, seeds and shade can have on green roof plants we should also remember certain trees can bring distinct advantages to a green roof or nearby permaculture garden.

Leaves on the Green Roof can exert both Allelopathic and/or anti-Allelopathic influences

One comment suggested we should take into account the addition of organic matter from leaves, replacing lost or broken down compost.

Trees or adjacent shrubs that stimulate growth through their presence, leaf or sap drop or other factors are commonly referred to as possessing 'Anti-Allelopathic' properties.  An anti-allelopath encourages nearby plant growth.  Actually this is a big complicated name describing a common simple practice - composting.

Chinese tallow tree, Triadica sebifera, a terribly invasive species here in Florida and across tropical areas is rated as one of the best anti-Allelopaths, her leaves and sap encouraging adjacent plants to grow as though fertilizer has just been aded to their base.

Leaves can be very useful on the rooftop garden, green roof or in the ground level permaculture garden!  Leaves cool the soil, promote soil moisture content, provide organic matter (good for bacterial breakdown of pollutants) and supply micronutrients, can adjust  pH and cation exchange potential.

No leaves?  May not be too glamorous yet very practical ( remember Louis Sullivan and functionalist architecture) collecting your neighbor's bagged up yard leaves can benefit your green roof or permaculture garden and benefit your wallet.

As mentioned, cation exchange capacity and pH are two important variables of a green roof. Additionally, leaf compost can add valuable trace minerals needed by the rooftop plants.  Some trees, including certain maples containing high sugar content in their sap and leaves possess an extremely low pH, in the range of approximately 4.5 to 5.5.  Other leaves such as white ash and popular may have quite high pH's, approaching 8.0 or above.

American sycamore leaves shown here can exert Allelopathic influences

Leaf compost typically contains twice the amount of trace minerals by weight as does horse manure.  

Interestingly, leaves from different species of trees offer varying characteristics. While ash leaves are relative neutral in pH, some maple species leaves are documented to possess a pH of around 4.5. 

Research also shows use of properly composted leaves greatly increases the cation exchange capacity of soils. One of the important functions needed in green roof soil media is cation exchange capacity.

Though varying opinions of organic compost value to green roofs exist throughout the industry, many believe organic material in the soil media is highly beneficial to green roof plants.

Massachusetts' state DEP has published an informative paper on the value of leaves for compost, including discussing issues and benefits, nitrogen to carbon ratios, composting processes and more.  This information is helpful to those just starting composting or those interested in studying potential allelopathic or anti-allelopathic effects on their green roof, living wall or ground level permaculture bed.

Fossa alterna technology also relies heavily on leaf use and in turn has produced informative leaf nutrient information.

Remember, green roofs are individual ecosystems, intricate webs of life with complex interactions.

Flat roofs with poor drainage may or may not require lower organic content to prevent water saturation and facilitate drainage.

Sloped roofs may function appropriately with high organic content.

Again, if you lack adjacent anti-allelopathic trees then go out about the cityand find leaf waste destined for the landfill.  Collecting heavy duty garbage bags filled with fresh raked leaves (we avoid those lawns heavily treated with fertilizers and herbicides/pesticides - those lawns are easy to spot here in the US due to the small advertising signs the lawn companies stick in the lawn after a fertilizer application - and speaking of lawns and fertilizers - a short must-see video of the history of the American Lawn will have you rolling in your chair and scratching your head at the same time can be viewed here) is a positive step for the environment.

Other benefits include;

  • Free highly effective cation exchange capacity supplements from the leaf compost
  • Free organic matter from the leaf compost
  • Free trace minerals from the leaf compost
  • Free pH adjustment material from the leaf compost (this is especially important when using higher pH soil media or media high in calcium)
  • Free garbage bags
  • And a lesson to your children riding with you to scavenge that recycling is more important than pride. :)

Thursday, November 24, 2011

Green Roof Photos for a Florida Thanksgiving

Happy Thanksgiving ya'll from the hot & dry deep south.  Enjoy the fresh, just snapped Green Roof photos!  Blessings to all.

Rooftop Permaculture - Fresh, Dew Kissed Greens on the Green Roof by MetroVerde

Pink Muhly still blooming in late November on the Green Roof by MetroVerde 
Mint, Basil, Garlic & Clover on the MetroVerde GreenRoof 
Autumns leaves decorate the MetroVerde Green Roof

MetroVerde  Green Roof Lemongrass & Salad Greens

MetroVerde Green Roofs are shallow and lightweight

Living Roof on the front porch of a home in the Riverside Avondale Historic Preservation District

MetroVerde's green roofs are nature irrigated and use many native wildflowers
Mint and Allium on the MetroVerde Green Roof

Wednesday, November 23, 2011

Green Roof Plant Design - Useful and Harmful Effects of Allelopathy

Plant matter such as bark, leaves, twigs, nuts and pollen can act as a herbicide, interfering with other plant's cell division, nutrient uptake, photosynthesis, et al.   Some plants have strong effects on other plants, preventing growth in some and encouraging growth in others.

American Sycamore leaves are known for allelopathic properties (maybe they will surpress the Bidens alba!)

The University of Florida defines allelopathy as, "beneficial or harmful effects of one plant on another plant, both crop and weed species, by the release of chemicals from plant parts by leaching, root exudation, volatilization, residue decomposition and other processes in both natural and agricultural systems."

Plant matter such as bark, leaves, twigs, nuts and pollen can act as a herbicide, interfering with other plant's cell division, nutrient uptake, photosynthesis, et al.

An allelopathic tree usually exerts  negative influence on adjacent vegetaion via a number of different processes, including;
  • Fog & dew drip
  • Leaf litter
  • Volatilization 
  • Sap drip
  • Pollen
  • Other biological processes
Understanding allelopathy is especially important for green roofs and rooftop gardens with surrounding, adjacent taller trees.  Allelopathy can greatly surpress rooftop food production.

According to the University of Georgia, School of Forestry Resources , there are a number of significant allelopathic trees requiring attention when planting other plants nearby.  They include;

Strong Potential for Allelopathic Impacts 
Acacia spp
Acer saccharum
Ailanthus altissima
Celtis laevigata
Celtis occidentalis
Eucalyptus camaldulensis
Eucalyptus globulus
Eucalyptus spp 
Juglans cinerea
Juglans nigra
Leucaena spp
Myrica cerifera
Picea engelmannii
Platanus occidentalis 
Populus deltoides
Prosopis juliflora
Prunus cornuta
Prunus serotina leaf 
Quercus falcata leaf 
Quercus marilandica
Quercus rubra
Quercus stellata
Robinia pseudoacacia
Sassafras albidum
Ulmus americana

Moderate Potential for Allelopathic Impacts
Abies amabilis
Abies balsamea
Abies grandis
Acer circinatum
Acer negundo
Acer platanoides
Acer pseudoplatanus
Acer saccharinum
Aesculus glabra
Aesculus hippocastanum
Aesculus octandra
Arbutus menziesii
Carya illinoensis
Carya ovate
Corylus spp
Crataegus spp
Fraxinus excelsior
Ginkgo biloba
Gleditsia triacanthos
Juniperus monosperma
Juniperus scopulorum
Kalmia spp
Picea spp
Pinus banksiana
Pinus contorta
Pinus densiflora
Pinus edulis
Pinus elliotii
Pinus monophylla
Pinus ponderosa
Pinus sylvestris
Prunus pumila
Quercus alba
Quercus borealis
Quercus douglasii
Quercus gambelii
Quercus michauxii
Quercus shumardii
Rhododendron maximum
Rhus copallina 
Sorbus sitchensis
Tsuga canadensi

Slight Potential for Allelopathic Impacts
Abies concolor
Aesculus spp
Betula pendula
Carpinus spp
Casuarina spp
Cupressus macrocarpa
Fagus spp
Fraxinus spp
Larix decidua
Picea excelso
Pinus palustris
Pinus spp
Populus spp
Pseudotsuga menziesii
Quercus petraea
Quercus robur
Quercus rubra
Salix pellita
Sambucus racemosa
Sequoia sempervirens
Taxus brevifolia
Thuja plicata
Tilia americana
Tilia cordata
Tilia planifolia
Ulmus laevis
Ulmus parvifolia
Umbellularia californica

Adjacent to the Breaking Ground Green Roof (see photo above) there are American Sycamores,  Platanus occidentalis located in the southeastern and southwestern corners of the living roof.  The American Sycamore can produce significant allelopathic influence on adjacent green roof plants.  Data exists showing the active ingredients, scopoletin and chlorogenic acid found in the Sycamore leaf may    interfere with the ability of stomata on certain plant's leaves to function.

Interestingly, according to the University of Florida's IFAS publication referenced above, allelopathic properties can also be used strategically to control certain weeds, i.e. dried mango leaves surpress nutsedge tubers from sprouting.

Finally, good green roof design incorporates into design the potential and foreseeable effects of adjacent trees and other vegetation.  Recognizing and dealing with a potential allelopathic problems during design can save months or years of not knowing why a green roof is barely surviving.

Know the basics of plant allelopathy is you intend to work in green roof design!

Tuesday, November 22, 2011

Fertilizing Green Roofs? Stop Now!

Did you know your industrial fertilizers you are spreading across your rooftop garden contain Persistent Organic Pollutants (POPs)?  Or are we denying the many silent environmental and health impacts of POPs.

Having read the article posted by @psustentavel on Twitter - click here for the article about Persistent Organic Pollutants - the imagery of 'inorganic chemical 'fertilizers across countless green roofs,  the use of drinking water for irrigation - even backup irrigation - and the reckless abandon with which we use non-native species for landscapes, including those on rooftops, made me think - in our rush to install green roofs atop buildings, are we too creating a chronic issue someone else will have to pay for?

The value of green roofs is unquestionable.  There is solid scientific data to back up claimed benefits of habitat creation, carbon sequestration, oxygen production. greenhouse gas reduction, heat island effect tempering, cleaning of stormwater, integrated pest management and so much more.

Florida Extensive Green Roof Nature Irrigated

There is no doubt about the value properly designed and maintained green roofs can bring to the Urban Core.

Green roofs can be used to support Urban Permaculture - small scale, individualized rooftop farming operations providing food, fiber and medicine to city residents.

And many urban areas around the world are moving ahead with plans to increase urban agriculture.  Singapore, for example, produces 25% of the entire city's vegetable crop within the city limits. For a fascinating look at the importance of urban permaculture  read's white paper entitled Urban Agriculture and Community Food Security in the United States; Farming From the City Center to the Urban Fringe.

Rooftops are the new frontier of real estate in many urban areas.  Cities with limited available ground level real estate have acres of open rooftops.

Vegetated and green roofs are increasing in popularity, showing an impressive growth rate trend over the past decade.  According to, public awareness of and interest in green roofs is steadily growing.

Yet in our noble rush to restore volumetric green to the urban core we hopefully will recognize the potential environmental costs associated with mass production of green roofs.  The 'One Size Fits All' approach to green rooftops will not work for the worlds vastly different ecosystems.  Sadly and reminiscent of mega-agriculture's damaging past practices, we as an industry turn to potent chemicals to fertilize, control pests and then use much needed drinking water to either irrigate or serve as backup irrigation.

Independent and craftsman-like green roof design and construction could disappear.

As with the POPs causing health issues in Pakistan and other places, our indiscriminate use of hardy invasive species, potentially toxic chemical fertilizers, pesticides and herbicides on green roofs is a Ponzi Scheme our children too will pay for.

Importantly, we as an industry have already moved far in the direction of ecologically inappropriate and environmentally dangerous green roof design.  Florida's FDEP green roof in Pensacola, Florida possesses a large drip irrigation system, backed up with potable drinking water and planted with slow-release fertilizer compounds and soil amendments.

As in hidden environmental consequences associated with corporate profitability, denial of reality is the basis of success.  Though the 'green' benefits of the FDEP green roof are often touted in the media - the fact that chemical fertilizers are applied and potentially damaging to Escambia Bay's ecosystem are hidden.

Yet FDEP is fully aware of the environmental problems resulting from POPs, fertilization and pesticide use on green roofs.  In the proposed, new State of Florida Stormwater Applicant's Handbook,   FDEP allows green roof credit for volume retention of stormwater only (no water quality credit),  and recognizes fertilizers and pesticides will be used on green roofs (why no water quality credit is given), an approach we must reject.  Moreover, FDEP is requiring the purchase and use of a 'pollution control media' made from ground up automobile tires under the green roof soil media to keep the fertilizer's nutrients on the roof.

Over time and as water evaporates, added pesticides, herbicides and fertilizers will concentrate back into the surface waters and become an issue for our children.

In the rush to add volumetric green to the Urban Core, the POP issue could easily go unnoticed.

Temper the hurry to install a green roof with the knowledge of a local native species botanist and a soils expert.  Rather than ordering large amounts of hothouse pampered plant material, find a local nursery with individual plants acclimated to the climate.

Green roofs can be crafted to add artistic, educational, ecological and ethnobotanical value.

But we must first reject the incorrect notion that green roofs must be fertilized, irrigated with drinking water and doused in pesticides.

Green Roof Plants - What Makes Roots Happy?

Removing older green roofs to allow for a new project has opened my eyes to the way green roof plant roots grow.  Root growth science is also know as 'root architecture'.  

As you can see, roots do not like to be constrained.  Though all roofs have a perimeter and roots must eventually reach a boundary, allowing the plants to reach out for  nutrients and water offers many benefits!

Tomato plant roots reaching out horizontally in the Green Roof hurricane weave

Having grown plants in pots for decades I can say with no uncertainty root bound plants are prone to disease and do not preform well in the long term.
Pot bound roots spiral around and around looking for room to grow
Green Roof trays must be large to prevent root binding patterns

Normal root architecture is best achieved by open growing systems on Green Roofs
To me, a photo is worth a thousand words and it is easy for me to see how roots want to stretch out.  Of course we've discussed the many benefits of horizontal root architecture in previous posts.  An example  of a shallow green roof application can be found here.

Let your green roof roots grow.  If you use a tray system make sure the trays allow for root crossover through adequate openings.

Roots need oxygen too.  When roots grow too deep or are strangled by other roots due to a lack of horizontal growing room the plants can suffer.  Providing adequate horizontal growing room ensures good plant development, unless you are using tap root plants (not too many of these are appropriate for green roofs).

Monday, November 21, 2011

Green Roof Plant Design - Heliotropoism, Diaheliotropoism and Paraheliotroposim

Understanding photosynthesis processes in green roof plants is crucial to the green roof designer and we have discussed the difference between C3, C4 and CAM photosynthesis processes in prior notes, including;
Yet nature is complicated and does not limit herself in resisting environmental stressor conditions to just the above three types of photosynthesis processes.

Cowpeas and other plants for example possess the ability to adjust their leaves position to either increase or decrease the amount of leaf surface area receiving direct sunlight.
Under Intense Sunlight Leaves Fold to Prevent Desiccation

Under optimal Sunlight C3 Leaves Open Widely

Under Optimal Sunlight Conditions C3 Leaves Open Widely
Heliotropoism is the term used to describe a plant's actions when it orients leaves to receive more sunlight and thereby increasing photosynthesis capabilities, i.e. - more CO2 fixation.

Diaheliotropoism describes a plant whose leaves actually track the sun'd path, maximizing solar contact.

Paraheliotroposim denotes a plants actions similar to the above photographs.  During parahelioproposim, plants may fold or move their leaves to either;

  • Minimize solar contact, or
  • Minimize total leaf surface area,
either way reducing water loss and preventing desiccation.

Though C3 plants such as the beans - and most other of the world's food plants except the grasses, maize, and sorghum - do not possess as complicated a multi-cellular Calvin Cycle as C4 plants and are more susceptible to drought, they - through Heliotropism biomechanisms they do possess their own unique desiccation prevention mechanisms.

Green Roof Removal - Exploring Underneath Seven Year old #GreenRoof

We recently removed a living roof installed in 2005 over a sloped asphalt shingle roof here in Florida to accomodate a new project.  Of course I was very interested to see how the underlying shingles had fared for approximately seven years under a heavily used green roof supporting rooftop permaculture (tomatoes, allium and more).

Not surprisingly, the asphalt shingles looked as new as the day the living roof was installed in 2005.  Green roofs protect underlying roofs from ultraviolet rays and sun damage, effectively extending the roof life by years.

Green Roof plants removed in preparation for roof removal
Mat is lifted from the roof, exposing the roof barrier

Interesting root architecture, showing green roof plant root reach 

Roof is sloped with 5/12 drop

Root barrier is in excellent condition

Asphalt shingles appear like new, well preserved under the green roof

Green Roofs help preserve underlying roofs, extending functional life by years!

Friday, November 18, 2011

Rooftop Gardens in New York - RAD video!

New York Farm City from Petrina TV on Vimeo.

Living Walls, the work of Bob Chabot at the Jacksonville Zoo

Jacksonville, though certainly not a 'green' city, has a core group of individuals who want to see plants fill a concrete and asphalt void.

Bob Chabot who serves as Director of Horticulture and Facilities for the Jacksonville Zoo, as well as President of Greenscape of Jacksonville and Vice-President for the Association of Zoological Horticulture and I took a tour of his zoo gardens yesterday, focusing on several upcoming projects we are both involved in, the Lasalle Street native plant bioswale and living walls for the USGBC's North Florida Resource Center in downtown Jacksonville.

Bob Chabot & very healthy, flourishing lemongrass, Cymbopogon flexuosus
Of course, it helps to have all the mammal compost you ever need to grow great plants, however the design, combination and selection of native plants, Florida Friendly Plants and plants from around the world make the Jacksonville Zoo a virtual ethnobotanical and horticultural library.

Living Walls, Jacksonville Zoo,  Confederate Jasmine, Trachelosperum jasminoides
Living Walls, Jacksonville Zoo, Cross vine, Bignonia capreolata
Living Walls, Jacksonville Zoo, Cross vine, Bignonia capreolata
Bignonia and Trachelosperum offer several great advantages for vertical urban greenscapes.  They are both evergreen, non-invasive, provide habitat for wildlife, offer a stunning array of scents and visuality and importantly are drought tolerant.

We'll post updates on the various projects as they 'grow'.  In the meanwhile, if ever in Jacksonville be sure to take the time and tour the Jacksonville Zoo and Gardens.

Thursday, November 17, 2011

Green roofs and rainfall, nature's best irrigation

Green Roofs love rain
Rain is always welcomed by Florida green roofs.  Problem is for years now we haven't been receiving as much rain from the sky as we historically used to receive.

In fact, the Jacksonville and other areas of Florida and the Southeastern US, such as Houston and others are experiencing long term serious drought.

So when rain visits here, the green roof systems and plants must take advantage of every precious drop of water.

Last night we received about 15mm of rainfall, a little over one half inch.  Since all of our green roof systems are shallow in depth, I was confident the plant roots had an opportunity to adsorb a good amount of water.

Curious though to just how much water some our potted plants received, I ventured out into the nursery and selected a plant potted up in a one gallon container and removed the plant, examining the rootball for moisture.

Green Roof plants, Florida's rainfall events do not allow for much water adsorption anymore
As the photo shows, the top ten to twenty millimeters was wet.  Beyond fifty millimeters or so the roots were bone dry.

Horizontal roof architecture for green roofs has advantages, particularly if the green roof lies in the hot and dry climates of the world.  Horizontal root architecture is discussed here.

So though shallow roofs may not be the answer for all green roof applications, they have established themselves as viable alternatives in hot and dry climates, providing lightweight potential, lower cost, beauty, habitat and stormwater attenuation.

Tuesday, November 15, 2011