The Walls Are Alive

For privacy, quiet and insulation, consider a living wall

You’ve landscaped, gardened, and perhaps even planted your roof. Now consider another opportunity for plantscapes: Vertical planting–on walls.

Growing “green walls” or “living walls” provides small-footprint gardens as well as insulating and beautifying greenery that can disguise the most uninspiring walls and serve as a delightful alternative to conventional fencing.

They can provide privacy, sound barriers, habitat, moisture, and shade in addition to gardens that can provide flowers, fruits and vegetables. They can even naturally filter or evaporate rooftop runoff and wastewater, helping to take a load off stormwater and wastewater systems and protecting rivers and streams.

Living walls differ from trellises, and ivy- and climbing plant-covered walls in that they feature growing medium that allows plants to take root in the wall, not just at the base of it.

There are a variety of ways to grow vertically, such as garden walls, green walls, green eco-walls, wall planters, and hydroponics. Garden walls and green walls are perhaps the easiest and most versatile.

Garden walls

Garden walls are essentially gardens turned on end.

San Francisco Bay area garden wall designer Ahmad Hassan essentially makes a soil sandwich held up with welded wire. Four-foot-high galvanized welded wire mesh, such as that typically used to reinforce concrete, is rolled out on a tarp or newspaper. It can be spray-painted brown or dark green to blend in with the greenery it will support. When dry, it is spread with shredded redwood mulch and wet sphagnum moss for aesthetics. That is followed by a layer of sod, which provides a sheet of soil over which he recommends spreading some soil with a high clay content to hold moisture. Soaker hose or drip-irrigation line is snaked through the top one foot of the wall to provide moisture, although in moist climates this may not be necessary. Hassan prefers 1/4” hose with emitters spaced 12 inches apart. An alternative is to install bubblers at the very top of the wall. The water will trickle down through the wall to the rest of the wall. The sod is tied to the wire mesh upholstery style with zip ties. The wall is then picked up, stood upright and attached to posts firmly embedded in the ground with cement bases.

The garden wall is attached to the front of the posts, and another sheet of wire mesh goes on the back, hiding the posts. It’s filled with mulch, sod and soil to fill it out.

Three-inch holes are cut into the wire mesh in which plants are inserted at least one foot apart.

Many varieties of short-stemmed plants can be planted in the wall. Hassan favors drought-resistant varieties such as marguerite daisies, erigeron daisies, old varieties of geraniums, rosemary, lavender, ivy, lantana, even moss, vinca, and ice plants. For low-water varieties, choose succulents such as hens and chicks and sedums and fast-spreading ground covers like creeping thyme and creeping jenny. Climbing vines such as the fast-growing white potato, can be planted in the wall or in the ground in front of it and trained up the wall. For a softer line, plant the ground in front of the wall with tall plants against the wall and successively lower-growing plants in front of those.

In colder climates where the wall may be colder than the ground, green walls should be planted with hardy perennial ground covers. Otherwise, expect to replant it every year.

Wastewater-irrigated Green Walls

A similar design called GreenWall by Massachusetts-based Ecological Engineering Group uses up wastewater and organic waste in one integrated system. Waste wood, mulch and other chipped, shredded and chunky organics are packed between two galvanized wire mesh chain link fences placed 18 inches apart. Perforated small-diameter hard plastic or metal pipes drip graywater or pretreated wastewater into this organic filling which supports plants and over time, decomposes into compost. (For this reason, it’s best not to use flexible drip-irrigation tubing or hose, which might sink as the organics decomposes into composted humus.) The nitrogen and water in wastewater is a perfect carbon/nitrogen companion to the wood waste and so accelerates the aerobic decomposition. As the material composts and settles, more mulch and waste wood are added at the top. Coarse organic material, such as bark chunks, is preferred for the “filling” to create spaces for roots to take hold and for the graywater to be transformed by aerobic bacteria to used up by plants. Hungry and thirsty perennials are tucked into the material through the chain link fence.

Green Eco-Walls

Green Eco-Walls use green eco-roof media modified for vertical installation. This application is still experimental as most green eco-roof media is designed for no more than a 20-degree roof pitch. Many green eco-roof systems can be adapted by placing another layer of plastic mesh geotextile over the top layer of loose gravel or compost to anchor it and the plants. Drain gutters or green roof run-off into the top of the green eco-wall.

An instant green wall can be made by inserting plants into well-soaked sheets of two-inch coconut coir mat sewn with pockets filled humus or lightweight aggregate such as expanded shale or perlite to hold plants. Plant roots will spread into the coir mesh.

Wall Planters and Hydroponics

Filling a wall with hanging planters or planter shelves is an age-old method of greening up a wall. One day, such systems will do double-duty, serving as both cladding and providing water cleansing for buildings.

In Germany, wall planters that drain sequentially from planter to planter are part of water-cleaning systems called “vertical swamps” or “vertical wetlands.” You can make your own vertical wetland with flat-backed planters, baskets lined with coconut coir mat, or hanging cones that drain into each other via pipe or free drainage.

Vertical hydroponic walls are a common growing method for the greenhouse agriculture industry. A Columbia University researcher, however, suggests that vertical gardening, perhaps even on the sides of skyscrapers, will provide food in ever-growing cities. You can create your own wall of hydroponically grown greenery with a framework of plastic pipe into which plants in pots filled with stone, clay pellets or perlite are inserted into perforations. A pump or water drained from above cycles water through the system. As with all green walls, fertilizer should be added periodically.

Green walls provide a new dimension for reintroducing both the aesthetic and air- and water-filtering value of plants to the human-built environment. Next time you plan landscaping, think up as well as out.

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Carol Steinfeld is the author of The Composting Toilet System Book, Liquid Gold: The Lore & Logic of Using Urine to Grow Plants, and Reusing the Resource (New Society Publishing).