The first time I was in a tropical rainforest was in Costa Rica some 25 years ago… and I was blown away by the exuberance of the vegetation. The trees were so densely covered in epiphytic plants (plants that grow on other plants) that you couldn’t even see their bark. There were sometimes even plants growing on the leaves of bigger plants! Ferns, orchids, aroids, even cactus, all vying for space and light. It was magical!
I began thinking about the idea of creating a wall of greenery in my home by having plants grow on bark, just like in the jungle. And I could use some sort of irrigation system to drip water over the bark. But there was a complication. My wife thought it was just about the stupidest idea she had ever heard. A wall with water dripping over it? All she could imagine was slippery floors. And who ever heard of bark on a wall?
For years, I brought up the subject again and again, but no luck. She wouldn’t budge. Then, in 2002, on a trip to Bali (I lead garden tours, so travel extensively), we stayed at the Bali Mandira Beach Resort and the bathroom was actually more or less outdoors: a cubicle surrounded by stone walls… and ferns and moss had started to colonize the wall. My wife thought it was absolutely beautiful. When I told her that was what the plant wall would look like, she said, “What a great idea! Why didn’t you tell me about that before?”
It just so happened we had long dreamed using part of one of our bedrooms to enlarge our home’s tiny original bathroom. Well, the kids had just moved out, leaving us with extra bedrooms, and my wife now approved. So I incorporated the green wall into the general renovation plans.
The basic concept of my wall is simple enough: I built a water reservoir between the soon-to-be-installed double bathtub and wall and a pump carries water from the reservoir up to the top of the wall via a PVC pipe. The wall is covered in pieces of natural cork bark (called “cork flats”, that is, relatively flat sections of bark, available through orchid suppliers). When the pump is turned on, water is carried from the reservoir to the top of the wall, then then runs right across the wall via a horizontal PVC pipe. It then drips down over the cork through emitters (drippers) designed for drip irrigation, watering the epiphytic plants planted the bark. Any excess water ends up in the reservoir where it can then be recirculated. Of course, there is a drain designed to catch any overflow, plus a stopcock (as in a toilet), so if the water level drops, the reservoir will automatically fill up.
To prevent seepage, I used waterproof wallboard for the back wall, then painted it with waterproof coating to double the protection. Cork bark comes in irregular sizes, so assembling them to fit the wall was like putting together a giant jigsaw puzzle. However, with the help of a couple of tubes of brown silicone sealant acting as glue, the wall was soon assembled.
Not wanting the reservoir to be visible, I hid it from sight it with a custom-made metal grid, covering that with decorative stones. As water drips down off the wall, it flows through the stones into the reservoir.
Getting the Light Right
Were I to carry out this project under ideal circumstances, I would definitely choose a room with sunnier windows. However, because of the configuration of our house, the bathroom had to be on the north side. Furthermore, the room had only small windows, plus it was under tall spruce trees. In other words, there is little natural light reaching the wall. I used high intensity fluorescent lighting (T5 lamps) fixed to the ceiling as the primary light source. Even so, light decreases the further the lamp is from the plants, so the plants in the middle and lower parts of the wall only receive low light. This has been a major limiting factor in the plants I can grow.
Planting a Cork Wall
Putting plants on a cork wall is incredibly simple. Just staple the cutting to the wall and it will root, as the bark remains slightly moist at all times. (Epiphytic plants have roots that will cling to bark like glue once they start growing.)
Alternatively, you can wash the soil off an established plant and wrap its roots in sphagnum moss, then fix it to the wall with a piece of wire. It will soon produce new roots that attach to the bark. That technique leaves a mass of older roots that look unnatural, though. I prefer to add plants as cuttings.
A surprising number of plants that we grow as houseplants are actually epiphytes in the wild. I have great success with aroids (Philodendron, Anthurium, Monstera, Epipremnum and others), ferns (Adiantum, Polypodium, Microsorum, Phlebodium, etc.), gesneriads (Episcia and Saintpaulia), pileas (Pilea), rhizomatous begonias (Begonia), hoyas (Hoya) and epiphytic cacti (Rhipsalis).
I must admit I have been disappointed with the results I’ve have from orchids. Since most are epiphytic plants and grow on bark in the wild, I’d assumed they’d do well, but most petered out and died over time. I only have a few miniature Phalaenopsis left and they do bloom, but not as often as I had hoped. I put the blame on the light situation: I think my wall is just a bit too dark for most orchids. Also, this is a bathroom and therefore kept warm in all seasons, while many orchids like cooler winter temperatures.
Bromeliads likewise fail to thrive, yet most too are epiphytic plants. I’m not sure if the problem is low light or the hard water that drips over them (they prefer their water soft, that is, with few minerals). Both orchids and bromeliads would be well worth trying in a sunnier room.
Note ferns also sprout spontaneously, probably from spores wafting into the bathroom from ferns grown elsewhere in the house. I never planted any adiantums, for example, yet several now inhabit the wall.
There is practically none. A timer makes sure the plants are watered (I run the pump once a day for half an hour each time to imitate the climate of a rainforest) and I have found over the years that the plants provide their own organic matter, so no fertilizer is needed. (At any rate, epiphytic plants are renowned for their ability to grow with few nutrients). Mostly I remove yellowing leaves and every month or so, and do some selective pruning, as many of these plants are quite, well, enterprising.
Of course, the best part of the wall is the ambience that it gives to the bathroom that is, both my wife and I agree, the most beautiful room in our house. And I like to turn the pump on just before I start a bath so a few wayward raindrops fall on my head. It makes me feel like I’m bathing in of the hot springs in Arenal, Costa Rica.
My green wall has now been operating for over 12 years now without any major problems. I’ve had to replace a few pieces of cork bark in two sections, both on the edges of the wall, parts that get less moisture than the core. It would appear that cork lasts best when either continuously moist or totally dry, but when it goes back and forth from moist to dry, it becomes thin and tends to rots away.
How long can I expect cork bark to last in the spots that are humid? Artificial epiphyte trees covered in cork bark lasted 60 years at the Montreal Botanical Garden before needing replacement and since I won’t be around 60 years from now, honestly, that isn’t a major concern!