8 • The Southwest Portland Post
Dear EarthTalk: I’ve heard of green
roofs, but what are “green walls?”
– P. Spencer, Alcoa, TN
Green walls (also known as biowalls,
vertical gardens or vertical vegetated
complex walls) are wall structures
partly composed of or filled in with
growing plant matter.
More than just easy on the eyes, green
walls work like green roofs by filter-
ing air and water, soaking up carbon
dioxide and helping lessen the “heat
island” effect of urban areas while
reducing air conditioning costs in their
host buildings.
The self-proclaimed creator of the
vertical garden concept, French bota-
nist Patrick Blanc, pioneered the use
of hydroponic cultivation techniques.
Plants grow in an irrigated mineral
nutrient solution without the need for a
soil substrate to create large green wall
installations.
These installations thrive in residen-
tial settings and within larger public
structures and even office buildings
from Singapore to San Francisco and
points in between.
Blanc’s installations start by placing
a metal frame on a load-bearing wall
FEATURES
or structure. The frame supports a
10-millimeter-thick PVC plate, upon
which are stapled two 3-millimeter-
thick layers of polyamide felt.
“These layers mimic cliff-growing
mosses and support the roots of many
plants,” he says, adding that a network
of pipes and valves provides a nutrient
solution of dissolved minerals needed
for plant growth.
“The felt is soaked by capillary action
with this nutrient solution, which flows
down the wall by gravity.”
“The roots of the plants take up the
nutrients they need, and excess water is
collected at the bottom of the wall by a
gutter before being re-injected into the
network of pipes: The system works in
a closed circuit.”
Plants are chosen for their ability to
grow in this type of environment and
depending on available light.
“Each vertical garden is a unique wall
composition of various types of plants
that has to take into account the specific
surroundings of the place in which it is
created,” says landscape architect Mi-
chael Hellgren, who founded the firm
Vertical Garden Design in 2004.
“It is not only the colorful interplay
between the plants on a ‘green wall’ that
is fascinating, but also the appearance
of the wall itself, which changes daily.”
Hellgren, who has designed and
implemented large green walls in his
home country of Sweden as well as in
Spain, Portugal and Italy, among other
locales, sources plants for his projects
from various climate zones around the
world.
His favorites are so called “litho-
phytes:” plants that can grow on rocks,
branches and tree trunks without nec-
January
Special!
December 2011
Green walls, or "vertical gardens," are walls partly composed of or filled in with
live plant matter. They filter air and water, soak up carbon dioxide and help
lessen the “heat island” effect of urban areas while reducing air conditioning
costs in their host buildings. Pictured: a vertical garden at the Anataeum Hotel
in London. (Photo courtesy of Niall Napier, Flickr)
essarily being rooted in soil. “Among
other things these climbing plants have
the enormous advantage of their roots
acting as excellent natural drainage on
the wall,” he adds.
While large “vertical gardens” are
surely impressive, critics question
the sustainability of such endeavors,
given the energy inputs needed to run
the pumps and other equipment used
to maintain proper nutrient and air
flows, and the emissions caused by the
manufacture and transport of special-
ized materials.
Also, larger green walls need more
water than rain alone can provide, and
thus don’t necessarily save water. But
as the field matures, practitioners are
finding wider arrays of plants to choose
from that are better at taking care of
themselves.
Practitioners are scaling back on in-
puts and supporting machinery with
the hope that one day many of the walls
will be self-sustaining gardens that
cleanse our dirty air and compromised
storm water.
CONTACTS: Patrick Blanc, www.
verticalgardenpatrickblanc.com; Verti-
cal Garden Design, www.verticalgar-
dendesign.com.
EarthTalk® is written and edited by
Roddy Scheer and Doug Moss and is a reg-
istered trademark of E - The Environmental
Magazine (www.emagazine.com). Send
questions to: earthtalk@emagazine.com.
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