Over the years I haven’t done a particularly good job writing about hydroponic based technology, more specifically hydroponic green walls. I would contribute that to the fact that beyond the work of the ever popular Patrick Blanc, the technology was still being developed for vertical walls.
I personally have found them a cumbersome maintenance project; however there have been advances in materials and easy applications, but not without a “fine line” between success and failure. I’m going to share some of my experiences and explain that “fine line” that includes some detailed variables.
One of Patrick Blanc's latest works in Berlin, Germany at the Düssman das KulturKaufhaus, 2011.
Like green walls in general, hydroponic techniques are not new; the Greek term “Hydro” means water and “Ponos” is labor. Even the gardens of Babylon had a pumping system to bring water to the top of the garden, letting it trickle back down to the lower pools.
Nature irrigates naturally occurring walls through runoff that collects nutrients from natural decomposition to feed the plants clinging to the sides of cliffs and other rock walls. In a previous article (The Original Green Living Wall: Basis for Great Design, September 26, 2010), I described the origin of green walls and the natural rock faces created by Mother Nature. Nutrients and minerals are created naturally, picked up by runoff as the roots are bathed in a nutrient rich solution. Sounds simple to recreate, right? Not so fast! We’re talking about Mother Nature here.
I have documented and studied naturally occurring green walls over the years. Since I live in upstate New York (USA), I am much more familiar with the local native plant types except for my time spent outside of Portland, Oregon hiking to Multnomah, Latourell, Wahkeena and Horsetail waterfalls along the Columbia River.
The walls I have studied here are the epitome of “Native Living Walls.”
Living wall by Mother Nature along the Larch Mountain trail OR, consisting of native plants including various lichen & ferns.
Before I continue let me make reference to the nomenclature of “Green Walls” as a general term, which is divided into “Green Facades” and “Living Walls.” Since living walls are defined by having the root system throughout the wall, naturally occurring green walls are defined as living walls.
A green façade is usually a 3d trellis like support structure with a climbing plant found at the base. In nature climbing plants are also naturally occurring however for the purpose of this article our focus is living walls.
Although my hiking has decreased to almost none over the past year due to knee surgeries, I still feel that naturally occurring living walls provide a spectacle only found in nature. Plants we see as common or to the untrained eye might seem like nothing more than moss and ferns. A close look displays an awesome range of colors and textures; to the touch on a hot summer day the walls are cooling and provide a haven for animals and insects of all kinds. Every wall I have seen up-close has contained a variety of liverworts, ferns, mushrooms, lichens and wild flowers.
Left to Right: Anomodon attenuatus (anomodon moss), Atrichum undulatum (undulate atrichum moss).
Left to Right: Dicranum fulvum (dicranum moss), Asplenium scolopendrium (Hart's-tongue fern) - this fern is on the New York State Threatened List and the majority of these can be found in New York State.
The pictures provide just a small sample of what can be found growing on the natural living walls. Without the use of synthetic fertilizers, this is natural hydroponics at its best.
Left, Right and Below: Aquilegia canadensis (wild columbine), Ilex verticillata (American winterberry), and Sedum spathulifolium ('Cape Blanco' stonecrop). This Sedum from Oregon is a favorite food for the pika (a small relation to the rabbit). In the spring look for a bright yellow flower that stands out against the lichen.
Trying to duplicate Mother Nature’s efforts is no easy task. In nature plants adapt and are conducive to the environment; they are naturally at home.
Installing a hydroponic living wall is relatively easy; the challenge is to meet all the needs of a plant pallet that is part of the man made ecosystem - totally unnatural and more times than not combining plants that are not of the same needs is the main reason for failures.
Hydroponic living walls are also much different than the traditional horizontal technology developed to grow food. For starters, the living walls are vertical unlike food producing units that are horizontal, even if they are “stacked” as towers and allow the vegetation to climb vertical (Green Façade).
Before we talk about the DIY materials and “How To” part, let’s start with the types of hydroponic systems available. There are active and passive hydroponic systems, easily remembered because “active” means with a mechanical pump (which is the common for hydroponic living walls). In an active system, moving water is infused with chemical nutrients as it passes over the roots. A passive system works without a pump and utilizes a wicking fabric or some type of inorganic media that that draws water to the roots. The green wall systems I have had the opportunity to trial and work with have a combination of materials, everything from felt, to cleaning scrub pads (mineral wool), plastic, poly vinyl chloride (PVC) and coco husk, and they all rely on a mechanical means (active system).
I have not found one single combination of products and techniques that make hydroponic green walls a foolproof method. Some are much more successful than others but not without attention to detail and intensive maintenance requirements. In a natural occurring living wall the plants that are native to the surroundings are adapted to the conditions. “Conditions” refer to elevation, lighting, nutrient availability and in nature only plants that are adapted to the present conditions will continue to thrive. In the living wall the task of plant survival is put on the installer, system type and the expertise of the maintenance technician. Just because you are a landscaper or interior plant company, don’t assume you’re going to be able to jump right in and master hydroponic living walls - there is a learning curve.
I do have relationships in the industry, some of them with national companies; they maintain both media /soil based walls and other hydroponic walls. The maintenance on the hydroponic walls is a break-even scenario for them because of the higher than average maintenance needs. The variables and conditions are ever changing and having the ability to meet the maintenance needs and upkeep is an education only experience can bring.
Here is that “fine line” between success and failure. Many variables are under constant monitoring in order to be successful. Hydroponic living walls are seldom 100% lush and thriving all the time because of the ever changing variables with very little room for error. Even a slight change in temperature can disrupt the dynamics of the wall causing massive areas of die-off; we will talk more on monitoring the walls later.
Hydroponic Living Wall: Basics
Hydroponics require many variables to come together in sync in order to be successful. My own reading suggests that experience and education are a must before diving into hydroponic growing. For the most part, common landscapers and indoor plant companies are usually not at the level of expertise when they decide to either install or take on the maintenance of a hydroponic living wall. Medias / root support structures, clean water, temperatures, pH levels, lighting, nutrient solutions, and oxygen exchange (oxygen to nutrient ratios), are part of the synchronization of successful hydroponic walls.
Hydroponic living walls start with some type of waterproofing to protect the structure behind the wall. There are common water proofing membranes, peel and stick applications, PVC sheets or in some cases I have seen layers of felt stapled directly to a concrete wall.
Felt fabrics, coco husk and porous sheets of scrub pads (mineral or rock wool) and porous foam are the most popular types of rooting media materials. There are many varieties of applications for each of these products – again, I’m not partial to one particular material and I have seen various results with some better than others.
Left to Right: hydroponic capillary mat; felt fabric; capillary fabric with plastic lining and geo-textile backing (manufacturers unknown); http://www.therange.co.uk.
Deciding on what fabric or media to use can only come through experience. Personally I have documented and found high amounts of root and crown rot in all the media types shown here.
Left: 3M Doodlebug close up, 56” wide, by 42 yards long @ $32 per yard; purchase information contact: Joe Koszarek, Beacon Lighthouse Inc.; email@example.com. Right: Nedlaw Hydroponic Living Wall constructed from two layers of similar 3M Doodlebug scrub pads in larger rolls prior to being cut.
Coco husk block inserted into a geo-textile bag by GSky.
Left: Polyester weave (manufacturer unknown); Right: open cell polymer foam blocks similar use by Eco-Walls; purchase information contact: Chi Meng http://www.chimeng.com.tw
Avoiding Root Rot & Other Potential Issues
According to Wikipedia, "In hydroponic systems inside greenhouses, where extensive monocultures of plants are maintained in plant nutrient solution (containing nitrogen, potassium, phosphate, and micronutrients) that is continuously recirculated to the crop, Pythium spp. cause extensive and devastating root rot and is often difficult to prevent or control."
Root rot can occur in hydroponic applications, if the water is not properly aerated. The root rot affects entire operations within two to four days due to the inherent nature of hydroponic systems where roots are nakedly exposed to the water medium, in which the zoospores can move freely. (http://en.wikipedia.org/wiki/Pythium)
Hydroponic living wall showing signs of both crown and root rot.
Symptoms include leaf drop, yellowing & discoloration.
It is typical that root rot is the result of an anaerobic environment. (As we continue I will explain the importance of balancing nutrients and oxygen exchange.)
Root rot evident sandwiched between two layers of 3M Doodlebug.
Distinct onset of root rot, this particular plant will last another 24-72 hours.
Other factors include: unsterilized tools and equipment, unfiltered water, dead roots and leaves, other infected plant material. As a former landscape contractor I know personally what it would take to sterilize my tools to work on such a wall - frankly, it may be too much trouble.
This is one of the reasons the cost of maintenance is high. The preventative labor is equal to the actual labor pruning and replacing of plants.
Hydroponic Living Wall utilizing open cell foam showing plant loss due to crown and root rot.
Obvious signs of yellow and discolored leaves, leaf loss and plant deterioration.
This hydroponic living wall shows a variety of symptoms that include: Root rot, discoloration, crown rot and algae build up. If you look closely you will see some naturally formed lichen and the burnt tips of the leaves that may be caused by salt build up or over fertilizing.
Because of the constant presence of water, hydroponic living wall media can become a breeding ground for algae and gnats. Keeping the plants healthy, vigorous and stress-free is the best "cure" against Pythium. Pythium is almost impossible to 100% eradicate from an infected system; this involves starting completely over with new plants, containers, equipment, etc.
To remedy the wall you will have to disinfect the entire system. Manual scrubbing and bleach might be necessary, adding tap water, and disinfecting the water with strong hydrogen peroxide (H2O2). The solution will require 100ppm to kill pythium - however, this can also kill small plants. Wait 24 hours for H2O2 to dissipate to a safe level; do not add more water to system!
Add only H2O2-treated water, add nutrients and beneficial enzymes. The aerobic-loving enzymes will colonize the sterilized medium and system, hopefully displacing any of the anaerobic bacteria. Starting with a clean system is the best prevention.
Below you can see leaf build up at the drain (right) and fallen leaves rotting on the left. These dead leaves become food for the Pythium. This is also true with algae. Algae will eventually dry, die and become organic material, fueling Pythium fungus. Once started it becomes a vicious cycle without sterilizing the entire wall. There are chemical / biological preventatives; I would suggest going to talk with your local hydroponic store.
Left: Leaf build up; Right: Rotting leaves.
Once you decide on a rooting media, having clean water is not an option. Some professional growers will use distilled water and this is much more expensive; however, hydroponics are very sensitive to salts, pH and changing variables including temperature. The water is a vehicle that transports a nutrient solution to the top of the wall via a pumping system and allows it to saturate the rooting media via gravity from the top down while bathing the roots.
All plants need key macronutrients: Nitrogen, Phosphorus and Potassium lead the list of “must have” chemicals:
Nitrogen (N) —promotes vegetative growth Phosphorus (P)—contributes to healthy roots and flower blooms Potassium (K)—important to fight off disease and resistance to pests Sulfur (S)—health and improved color of the leaves Calcium (Ca)—promotes new root growth Magnesium (Mg) chlorophyll—contains a Mg ion that improves food production
In commercial fertilizers the N, P & K are depicted by numbers in ratio to the weight of each one. For example 10-10-10 is a balanced ratio of N, P & K. In contrast, 25-5-5 will provide a quick rapid greening of the visual leafy portion of the plant with only 1/5th the P & K. Boron (B), copper (Cu), cobalt (Co), iron (Fe) manganese (Mn), molybdenum (Mo), and zinc (Zn) are micronutrients responsible for a myriad of tasks including: cell wall development, nitrogen and sugar metabolism, protein synthesis and water loss just to name a few.
Vegetation acquires these micronutrients directly from natural growing media; commercial producers of fertilizer do not include them for typical landscape and crop applications, but because the hydroponic technologies for living walls do not include a growing media that can hold nutrients, the nutrient solution MUST include these essential micronutrients.
This is where inexperience becomes costly. If you are not trained nor have experience with vegetation for hydroponic living walls, the risk may outweigh the glory. This is not a project you want to experiment with a client. You risk reputation and serious monetary loss simply through maintenance and plant replacement. I mentioned earlier we work with a very experienced indoor plant company who is happy to break even on the maintenance of the hydroponic living walls they maintain. They keep the wall as part of the overall maintenance account for the building. There are many over the counter pre mixed nutrient solutions available; contact your local hydroponic supplier for more details.
(For an interesting debate on Organic vs. Hydroponic Growing, visit Jungle Walls by Peter Kastan.)
Once you add plants, the variables will continue to grow from here, no pun of course. You have to find a balance between nutrient solutions, pH levels, temperatures, lighting, and dissolved oxygen. All of these variables must be in alignment for a hydroponic living wall to work.
pH is a scale from 1 to 14 that measures acid-to-alkaline balance: 1 being the most acidic, 7 is neutral and 14 is most alkaline. Every full point change in pH represents a 10-time increase or decrease in acidity or alkalinity. For example, soil or water with a pH of 5 is 10 times more acidic than water or soil with a pH of 6. Water with a pH of 5 is 100 times more acidic than water with a pH of 7. With a 10-fold difference between each point on the scale, accurate measurement and control is essential to a strong, healthy garden.
Most plants grow best with a pH between 6.5 - 7. Within this range, plants will absorb and process available nutrients most efficiently. If the pH is too low (acidic), salts bind nutrients chemically, and the roots are unable to absorb them and the plants won’t feed. On the flip side, an alkaline soil with a high pH causes nutrients to become unavailable. Toxic salt build up that limits water intake by roots also becomes a problem; get to know your water.
Hydroponic solutions perform best in a pH range a little lower than for soil. The ideal pH range for hydroponics is from 5.8 - 6.8, slightly acidic. A bi weekly test should be part of the maintenance process; adding products to pH up (potassium hydroxide and potassium carbonate) and pH down (Phosphoric acid) add cost to maintain the hydroponic living walls.
The amount of dissolved oxygen in a nutrient solution depends on the water temperature. Cold water can 'hold' more dissolved oxygen. A fully aerated solution at 20°C/68°F is 9 - 10ppm; at 30°C/86°F it's 7ppm. According to Dr. Lynette Morgan, Director of Research at SUNTEC International Hydroponic Consultants based in Manawatu, New Zealand, root oxygen requirements double for each 10°C rise in root system temperature (max 30°C/86°F).
The dilemma for the maintenance technician is that with a 10°C rise in temperature, root system oxygen requirements will double, while the oxygen carrying capacity of the solution will drop by over 25%! The nutrient dissolved oxygen is unable to supply the roots’ oxygen demands, leading to prolonged oxygen starvation. Oxygen starvation will result in slow growth, mineral deficiencies and root die-back. Oxygen starvation will stress the plant, leading to an eventual attack by opportunistic pathogens, such as ever-present pythium aka root rot. What Dr. Morgan is describing is the anaerobic environment that is the naturally occurring environment of hydroponic systems.
DIY Equipment & Set Up
For the most part the equipment needs are pretty simple. Assuming we are talking specifically about hydroponic green walls – I’m not going to talk about ebb and flow nor aeroponics - specifically we are utilizing a top feed configuration; water solution is pumped up and allowed to drip through the media back to a reservoir. Pending the size of your wall, freestanding or wall mounted, you need a reservoir, pump, inorganic media (what will physically hold the plants), test kits and sterile tools.
For a reservoir the basic of plastic containers will work fine depending on the size of your wall. Some more advanced applications also contribute to the cosmetics of the system; stainless steel and decorative pools are not uncommon but because of the sensitivity of the solution, the exposed reservoir is subject to becoming a catch all for garbage or debris immediately altering the dynamics of the pH.
As a word of caution, take careful consideration of your reservoir as it is the life line to the success of the wall. For larger walls and walls exposed to evaporation, a fill float can be retro fitted to the reservoir. The color of your reservoir will also play a part in the water temperatures. As we discussed earlier, higher water temps result in less oxygen!
There are also a variety of pumps available; my experience as a pond builder would lead me to the magnetic drive types that seem to last more over continuous use. When choosing a pump the key is to understand how much water you need to pump at what rate and the height you have to pump it. The key here is what we call the “Head Height” or maximum height the pump can push water. Head is measured in length and the pump capability of flow vs. height.
For example, the height from the top of the reservoir to the top of the wall is 10 feet. Searching the internet we find literally thousands of options. A statistical rule is to double the psi (pound per square inch) to determine the head in which the pump will pump zero gph (gallons per hour).
Table 1 shows the actual “Head Height” taking into account the reservoir is not part of the calculation. When configuring the actual pressure needed to reach the maximum height, the equal distribution of water going through the pump through the supply tube while it is in the water is equal to the water weight outside the tube until it exits the reservoir when gravity and the actual weight of the water in the tube come into play.
Table 2 is a common and easy means in which you can determine what the minimal needs would be to reach the height needed to irrigate your wall.
The life line of the system can be viewed as if it were a human. The pump is the heart, the tubes are veins and arteries, and the solution is the blood carrying nutrients to the remainder of the body - all must be in working order.
Constructing Your Hydroponic Living Wall
For the most part the steps are simple. Start with deciding on an area with good light and recirculation air flow. I have seen various types of armatures that are tapered from the top of the wall down to the bottomso we end up with about six inches from the bottom of the wall.
Figure 1. In most cases the walls are flat at a true 90 degrees. This tapered angle, however, will prevent the irrigation water from dripping off the leaves allowing it to follow the angle of the rooting media.
Figure 1: Vegetation angle
The following sequences of pictures are from Peter Kastan and provide a real hydroponic wall installation:
It may seem I'm pointing out a lot that go wrong with a hydroponic living wall system, but that is the point when dealing with a DIY project in particular. Of course, you have the option of choosing a patented hydroponic living wall system if you don't choose the DIY route. The greatest issue to consider here is scale and cost - of the system itself, installation, and maintenance plan.
While most of us probably can't afford Patrick Blanc and his Le Mur Végétal (Vertical Garden) living wall system, there are other proprietary hydroponic systems to consider - here a few:
There is a lot more to hydroponics than a simple pump and solution to feed the plants. And, living walls are not for the faint of heart when it comes to experimenting with someone else’s investment. When going DIY, my advice is to try various materials that are locally available, get advice from your local hydroponic supplier and set up your own trials and research.
I have pointed out some of the variables that will determine your project a success or a maintenance catastrophe. There is much more to the hydroponic living walls, including the highly variable topic of plant material – both inside and out – and I have only scratched the surface of the many highly advanced systems and applications.
George Irwin, The Green Wall Editor
George Irwin is the President and CEO of Green Living™ Technologies, International LLC (GLT) based in NY. Green Living™ Technologies is the only U.S. manufacturer of growing media based green wall and three types of green roof systems. Mr. Irwin is a former trainer for Green Roofs for Healthy Cities Green Walls 101.
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