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An Urban Vertical Garden: Building a Green Wall at St. Catherine’s

There’s something going on in the AC. Amidst the usual hustle and bustle (because, let’s face it, there’s always something fascinating going on in the AC), there are stacks of felt, piles of lumber, and students busily drilling, measuring, and mounting. Standing apart but within it all, like a ringmaster or an orchestra conductor, stands a large man in well-worn clothes and work boots. His accented voice is quiet but his directions are clear. The need for precision is clear, and the students are listening.

They are building a green wall. A “living wall” or “ecowall,” as it’s sometimes called, is a vertical garden. If you’re picturing a string of hanging plants – long fern fronds or trailing lobelias or philodendron vines – think again. This is a planted garden. Only it’s upright, growing perpendicularly to the ground, and apparently defying gravity with an experimental design technology that’s on the cutting edge of sustainable architecture.

Ferenc Szentkiralyi-Toth is a Hungarian landscape architect. His company, greenwall.pro, spent three years researching green walls in Europe and developed its own system in 2014. Since then, they have built approximately 15 green walls (including a massive 860sf wall in the Netherlands) but this wall at St. Catherine’s is his first in the U.S. His niece and nephew, both SCM students, were on a summer vacation in Hungary with their parents when conversation turned to AC projects and the idea of building a wall here began to germinate.

Climate matters for an outdoor green wall: temperature, wind, light, and humidity are the key factors. (Rainfall, perhaps surprisingly, doesn’t matter as much, as the vertical structure leads to drainage even in wet weather. Walls use drip irrigation to water the plants.) Szentkiralyi-Toth has tackled projects in far-flung locations ranging from Russia to the Middle East, but this is his first in a sub-tropical region. His passion for the subject is contagious. “Some systems are better for hotter weather, some for colder. This is a good way for us to test our product in a sub-tropical climate,” he said. “It’s a very young science, and there is not enough information and so many open questions like, for example, how to heat the root area during winter – there’s a German company that’s doing interesting things by watering with warm water. There’s so much to learn!”

The greenwall.pro system is a series of metal modules but “the transport costs would be horrible,” according to Szentkiralyi-Toth, so the wall at SCM is an updated homage of sorts to the original wall designed by Patrick Blanc, the “godfather” of modernizing and popularizing green walls about 15 years ago. The six -foot high wood wall features two layers of recycled fabric felt onto which “pockets” are attached. The pockets are a material made of recycled plastic bottles, widely used in the auto industry for sound insulation and seat batting. The metal modules bracket the wall and two irrigation pipes run across it. The felt is on supportive plastic and PVC Pond Foil and the entire edifice is a few inches removed from the backing so as to create an “air gap” for circulation, heating, airflow and drainage. Each pocket is filled with horticultural perlite into which a plant’s felt-wrapped root ball is placed. The AC community’s wind turbine will power the irrigation system’s computerized valves and timers.

Every aspect is a variable: the width of the air gap, the thickness of the felt, the construction of the metal modules, the spacing of the irrigation lines, the frequency of irrigation, the types of plants chosen. The SCM wall will feature herbs and flowers from the Home Grown Market. Szentkiralyi-Toth flew in to spend a week constructing the wall with the students and will depart before the herbs are purchased, but not without leaving recommendations. “Rosemary and sage do very well,” he said. “Thyme is a small grower. Slow. Not good.” And lavender? “I’ve tried so many times! On the wall, it doesn’t work and I don’t know why. We are learning all the time. All the experts, we are learning.”

And the experience of working with these students? “They’re much more open-minded than our students in Hungary!” laughed Szentkiralyi-Toth. “They ask questions and are curious, wanting detailed information. They will be picking and packing the root balls without my help and will be doing complicated maintenance. It’s been a very positive experience. Usually we’re always on the run, work at night, get it done quickly. It was good for me to slow down a bit, be patient. I wasn’t very good at first but I tried hard!” 

Jackson Uitenbroek was one of the AC students drawn to the activity outside. “I like to build things and this looked interesting,” he said. “I’d heard of vertical gardens but only seen hanging gardens and thought this would also have only plants like vines. This gives us more variety, options, and space. Our herb spiral is super-crowded and when it’s carrot season there isn’t much room for other things. This will give us lots of space.”

Uitenbroek hit on key feature of green walls: space. Modern urban planners and architects are increasingly turning to plants as sustainable solutions for ecological living. Plants reduce building temperature, improve air quality, and help purify slightly polluted water. Green walls are perfect for cities as they make good use of vertical surface areas to bring these benefits to tight spaces. Houston features a few noteworthy green walls: two 14-foot green walls with a total length of 250 feet are in the HEB store at San Felipe and the Houston Zoo features a green wall at its entrance.

St. Catherine’s green wall will be an ever-growing, on-going experiment. “It took 20 years before green roofs became a stable technology, after many failures and experiments, said Szentkiralyi-Toth. “[With green walls] we are in the first part of a growing technology.”