Green Roofs - Living Architecture Monitor - Spring 2012 - (Page 26)

PROJECT PROFILE A CALL fOR MAINTENANCE GROwING MEDIA fAILS TO PRODUCE by: kELLy LUCkETT, GRP I was recently requested to evaluate several green roof areas on a building in New York City. Six of the sections on the eighth floor have good southwestern sun exposure and one on the sixth floor is located on the northern side of a taller section of the building that keeps it shaded. All areas have between 6 and 8 inches of growth media depth. Four of the areas with good sun exposure have sedum planting strategies. The other two are propagated with a Geranium and Heuchera planting strategy. All have good color and appear healthy, however the space between plants has been exploited by clover, water grass, and weeds. The area with poor sun exposure is completely void of vegetation. ABOVE: Before & After Maintenance Break Down Images provided by: Kelly Luckett Poor sun exposure has created a microclimate that differs significantly from the areas with good sun exposure. The areas that receive winter time shading present issues for many evergreen sedums, as these plants rely on solar radiant heating during cold temperatures furthermore the winds that occur at this elevation exacerbate the effects of cold temperatures on soft plant tissue. Sedum planting strategies require well-draining soil. The growing media sample taken from this area was wet and there had been no precipitation for over five days. The duration of saturation typically increases with growing media depth. Shading can further prolong the duration of saturation. While increasing growing media depth is often intended to expand the plant palette and enhance plant survivability during dry weather, the 6 ½ inch soil depth could be contribut- ing to conditions unfavorable to the chosen sedum planting strategy. I recommend reducing the growth media depth to four inches and replacing the geotextile drainage course. Then, fertilize and replant with four pre-rooted plugs per square foot with an even mix of the following species: Sedum ternatum “Larinem Park,” Sedum kamtschaticum – “Yellow Stonecrop”, Sedum spurium “White Form”. These species were selected for their tolerance to shade. Shallow growing media depths allow natural mechanisms to reduce maintenance requirements and limit the intrusion of unwanted plant species. Sedum planting strategies are often selected for their survivability in shallow growing media depths. Many unwanted plant species will die naturally in four inch depths during periods of high heat and /or no rainfall. Increasing the depth can allow sedums to survive heat waves and periods of drought without supplemental irrigation, however, this often also creates an inviting environment for unwanted plant species. When the growing media depth is increased the maintenance required to remove and limit the spread of unwanted plant species increases significantly. Since the green roof system is porous and shallow growing media drains directly into the storm drainage system. Therefore, vigilant maintenance is required early on and annually (though lessening over time) to identify and remove juvenile sprouts prior to the production of seed. Unwanted plant species will build up a seed bank that can lie dormant for several years, making mechanical removal of unwanted plant species impractical. When considering remediation measures for these green roof areas, it is necessary to return LIVING ARCHITECTURE MONITOR / SPRING 2012 / 26

Table of Contents for the Digital Edition of Green Roofs - Living Architecture Monitor - Spring 2012

Green Roofs - Living Architecture Monitor - Spring 2012
Contents
From the Founder
Seen & Heard
Bookshelf
Special Thanks
On the Roof With…
Innovation
Urban Agriculture Summit in Toronto August 15th – 18th
Citiesalive in Chicago Oct 17th – 19th
Policy and Standards
We Asked Experts Their Opinions on Modular or Loose Laid Green Roof Systems, Check Out What They Said
I Guess Size Really Does Matter! — Growing Media Insights
Eleanor Mckinney Taking Austin by the Horns
New Industry Products
Green Roof Falls Flat in New York City
Green Roofing Leader Shows Industry What They’re Made Of! Tremco Incorporated
Plant Profile
New GRP’s
Professional Calendar
New Corporate Members
GRHC Buyers Guide
On Spec

Green Roofs - Living Architecture Monitor - Spring 2012

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