Mobile indoor green wall

Finally, after three years...

my plant vines have grown and spread to be green wall that I had hoped for. I'm not sure it would have taken as long if the plants were in a more humid, sunny climate, et cetera. But given our indoor Minnesota location - even with a southwest exposure - the vines have needed that amount of time to climb the six feet from the base to the top rungs of the metal grid supporting them.

The result has been worth the effort. And to be honest, I didn't have to wait three years to begin enjoying the green wall. The vines were already attractive when only half way up the trellis.

A metal grid is filled with mix of Epipremnum aureum cultivar "Marble Queen", Epipremnum aureum aka golden pothos, and Philodendron Brasil.

Architecture of the green wall

The initial intent of the project was to grow a green wall, in an apartment, that could be moved around to be able to clean underneath, and also to provide a mobile room divider for our open-plan loft. 

The green wall is built with basic metal shelving. The manufacturer offers an optional metal grid attachment intended for hanging implements such as pots or tools. Wheels allow the unit to be easily moved or rotated. The black color fits well in the context of the modern design of our building and the metal window hardware.

On the lowest of three shelves, plants were placed next to the grid to provide support for growing vines. The vines were trained to grow only on the exterior side of the grid. This allows individual plants to be more easily removed in the event they fail; trying to untangled vines could become an unpleasant chore and damaging to neighboring plant vines. Velcro strips were used to attach the growing vines to the metal grid; the strips allow easy adjustment or removal as the vines mature. But, other choices exist such as zip ties or simple wire twist ties,

The vine plants were placed into a standard growing tray designed to fit the shelf. The tray prevents the plant debris and excess water from spilling onto the floor. Also, although our automated irrigation system is not the topic of this post, the sides of the tray are high enough to contain all the water that might flood the tray from a burst irrigation hose - which has never yet happened. If an irrigation system is nowhere in your plan, then the tray rims could be much shallower than 4 inches these trays have.

Because the shelves are fitted with wheels, they can be moved around the apartment as needed. Most useful is the ability to rotate the rack 180 degrees to allow sunlight to access both sides of the green wall, typically on a weekly schedule. I enjoy viewing the the solid green wall of the vines, but the opposite view of the shelves is also very attractive with the sun streaming in through the stained glass-like vines, giving center stage to the companion plants - baskets of spider plants, orchids, Monsteras, and rattlesnake plants.

Lighting the plants at night really does add to the enjoyment. I light them more for the greenery than for the added growth. I find the brightness and color temperature of grow-lights to be too cold for my taste. I'll let the sunshine do the heavy lifting with plant growth. 

Lighting can be accomplished any number of ways. For example, attached to the grid of the green wall we've installed two adjustable and dimmable LED lights on gooseneck arms. These light the green wall plants on the outer surface. On the inner surface of the shelves my tech savvy partner installed strips of LED lights with adjustable color temperatures, and on dimmers to control the amount of light.

Finally, part of the architecture of the system is the type of flooring in the apartment. I was privileged to have had the choice to tile part of my apartment. It is of little concern to me if a bit of water spills onto the tile floor while I'm watering plants. The tile can resist the damp. But, wood seems fairly resistant too, under the right care. Having had plant shelves on both tile and wood floors for more than 5 years, I've never had water damage the wood floors - especially given the plant trays which contain most of the water overflow. I've spilled water on the wood floors more than a few times; I think a wood floor could be acceptable if the appropriate precautions are set up and the water is wiped up quickly. Carpet would be much more of a challenge if bits of debris and dirty water get down in the pile of the rug. I don't have any plants sitting on rugs, except one agave which I water once a month.

Wheeled metal shelves with grid attachment; plant pots sit in grower's trays.

Strips of dimmable LEDs light the inside shelves; gooseneck LEDs light the green wall.

Green Wall Plants

For the green wall I chose vining plants that have a good reputation for low-light conditions and drought tolerance. I also wanted plants that want to grow upwards onto some sort of support. I'm not a botanist, and my knowledge of plants is limited to what I have read or observed. Given my limited knowledge, I chose three species to grow into a variegated and quilted thicket: Epipremnum aureum (common name, golden pothos), Epipremnum aureum cultivar "Marble Queen", and Philodendron Brasil.

I have been surprised to observed the Marble Queen cultivar is the hardiest grower, with the largest leaves. It is counter intuitive because the leaves are heavily variegated with a lot of white marbling and the least amount of chlorophyll compared to the other plant varieties and their darker green leaves.

The plants were purchased in 4-inch pots. I let them grow, took cuttings, and repotted them into 6-inch pots before training them onto the metal grid. To date, I've only had to re-pot one of the six plants; it wasn't as much a chore as I had anticipated. I was able to lift the root ball out of the old pot and into the new larger pot without pulling the whole plant down off from the grid trellis.

Vines were directed to grow underneath the lower edge of the grid and only onto the outer facing surface to allow for maintenance.

Companion Plants

To complement the tapestry of the green wall, I chose Monstera deliciosa plants to climb up the corner posts of the self unit. They nicely lean out and blur the hard edges of the shelf posts. Sitting in the tray in front of the vine pots, which are positioned at the back of the shelf next to the grid, a variety of low-light tolerant plants are adapted to receiving light filtered through the leaves of the green wall; specifically, rattle snake plant (Geoppertia insignias), spider plants, and a small variety of orchids (phalaenopsis, vanda, dendrobium). It is particularly beneficial to be able to rotate the shelves to allow all of the plant some access to bright non-filtered light, if only on alternating weeks.

Vines are trained up the outside grid surface only, to prevent entanglement with the grid.

Pest Control

An inescapable fact of life for any houseplant is the constant threat of predation from a host of insects and mites - not to mention viruses and root rot. Mealybugs, scale insects, and spider mites have been my worst enemies. But, knock on wood, I've not had an infestation on any of my plants in several months. I am now careful to keep new or infested plants in strict quarantine until I'm reasonably convinced they are bug-free.

The first line of defense is the use of insecticidal soap and a sharp spray of water in the bath tub or shower stall to clean the leaves and stems from infested plants. And although this is effective to a large degree, it often doesn't completely remove all of the eggs and adults hidden in tiny crevices on the plants. Infested plants have to be repeatedly treated because eggs will hatch at intervals, typically 4 or 5 days apart.

Other methods need to be used in combination with soap and water.

To fight mealybugs and scale insects I've tried a few biologic control organisms. Lacewing larva and Cryptolaemus beetles did not work for me, the adults simply flew up to the window of the apartment, dehydrated and died (and I suspect there were too few mealybugs to keep them fed and attracted to the plants). However, Amblysieus californicus worked very well to eliminate spider mites from all of my plants.

Fungus gnats are hardly a concern of mine since they do not damage plants at all. However, I do treat the soil with pellets of mosquito repellent containing Bacillus thuringiensis which kills the gnat larvae. For the adult flies I use yellow sticky tapes.

For the mealybugs and scale I am embarrassed to admit I finally resorted to the systemic chemical imidacloprid. It is a neonicotinoid compound with acts a nerve agent for insects. It is rightly banned from use in farming in the EU since it it toxic to pollinators such as bees. Only a few States in the US have restrictions on the pesticide.

Neonicotinoids are not as much an issue for indoor plants. However, I will discontinue using this method since the compounds reside in soils and water for years. I've learned that even houseplant waste can be introduced into the outdoor environment and cause damage if it contains neonicotinoid compounds.

In the future, I will be experimenting with sprays of essential plant oils, such as spearmint and clove oils. These have been shown to be fairly effective in killing mealybugs and deterring them from spreading (unfortunately not as well as synthetic compounds).

Multiple racks of similar design allow a cohesive group, but with flexibility of position. The need for privacy drapes is almost eliminated.