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Canary
Wharf Tree Planting Details, London, England
Canary Wharf required a great deal of invention, not only
the overall creation of a place where before there was none,
but also in the details, especially the planting details that
would insure long-term, vigorous growth of the proposed parks
and street trees. The over-arching landscape concept was to
realize an instantly "mature", traditional City of London
landscape of treed streets and lush squares. These landscapes,
however, were to be on structure over parking, service roads,
and other occupied spaces. A method for planting mature trees
over structure had to be developed. In 1985, soil formulas
for planting over structure, and the required rooting volume
for mature trees, were just in the beginnings of exploration
and development.
The duel challenge: Determine sufficient
soil volume, and create a suitable soil mix. Working with
James Urban, then in the initial studies of determining safe
rooting volume (e.g. what volume of soil is required to grow
a tree to the desired size at "design maturity") and with contractor John Willerby, Dennis McGlade
determined the minimum soil volume necessary to successfully
grow large, well established urban trees in planters over
structure.
Traditionally, a lightweight planting mix would be utilized,
but, over time, a mix of this type, dependent upon peat and
perlite, would loose tremendous volume and offer insufficient
structural support for a large tree. The goal was to utilize
a soil formulation that would mimic a naturally occurring,
mineral based soil, one capable of sustaining the trees, offer
support in the windy site, and not loose volume over time.
Working in collaboration with Allan Hart, our London based
landscape architect and Boughton Loams, a planting soil fabricator
from the United Kingdom, such a mix was devised.
The example
illustrated shows the wedge-shaped pits over West Ferry Circus,
designed to be 4 meters wide by 6 to 8 meters long by 2 meters
deep (image 1). In an effort to aerate the full soil volume
and to maintain an aerobic condition throughout, the pits
were wrapped in aeration/drainage mat (image 2). Long horizontal
perforated aeration pipes were deployed along the base of
the pits and turned up through the centers of the pit, encouraging
air exchange throughout the soil volume. Where there is oxygen,
roots will grow (image 3). This emphasis on air exchange meant
that the entire volume of soil in the pit would be accessible
to the roots of the trees, and an anaerobic, putrefied soil
would be avoided. |
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Related links:www.canarywharf.com
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