Green walls have been popular for quite a while and continue to gain interest from growers looking to try something new and inspiring to look at. There are two main types: living walls, where the plants are rooted in pots or other types of containers; and living facades, where plants are rooted in the ground while they grow up and along a wall. Some gardeners combine the two to maximize the fullness of the wall and minimize the weight of the root systems on the wall.
When it comes to designing a green wall, there are many different things to consider, starting with whether the wall is inside or outside and how much sun the area gets. Too often there are complications the original design did not foresee and so did not deal with adequately. Because I have had many of these issues reported to me by my clients, I wanted to share the problems they ran into and some possible solutions.
Challenges of Building a Living Wall
- Too much energy or water use
- The weight of the plants is too much for the wall
- Soggy plants at the bottom of the wall
- Not enough soil for plants to grow properly
- Wrong type of plant for a wall or the location
- Irrigation system defects
- Trouble harvesting some of the plants due to location or height
- Trailing plants interfering with the plants below
- The plants at the top or in various sections are too dry
Read on for some design tips that will help ensure you don’t run into the challenges listed here. This article will focus on soil-based living wall systems.
Vertical Gardens: Containing the Roots
Before determining how you will contain the roots of your plants, look at the area where you want your wall and determine how big it is going to be, then see which soil structure system will work with that. There are so many ways to provide a structure for the soil for your living wall garden, and many manufacturers offer systems that come ready for soil and plants.
Rain gutters are one simple soil-housing solution. Each foot of 6-in.-deep rain gutter will hold about 0.4 cu. ft. of soil. This means you should plan to space most of your veggie plants 8-12-in. apart, depending on the size of the mature plant and your yield expectations. The design should include a gradual slope for each row to provide runoff and avoid overly wet root systems.
Once you have figured out how to contain the roots of your plants, providing them with enough soil to grow and thrive is crucial, otherwise weak plants with skimpy production will result. For example, tomatoes typically need about 1.5-cu.-ft. of soil to develop a root system capable of feeding the quantity of fruit it will produce.
A pepper plant is not as large, so 0.5-0.7 cu. ft. will usually do nicely. Figuring out the exact soil needs of your plants is more important when growing a living wall. For most “on the ground” situations, growers can simply provide more than is needed, but too much soil will make your living wall heavy and increase water and energy use without adding any benefits.
To simplify this a bit, consider how big you hope or expect the plant foliage to be. Make an estimate or do some research and find out. For plants like succulents, you can generally get away with smaller containers to hold roots, while big-leafed and heavy-fruiting plants need more. For larger plants, allow for one-third to one-quarter the cubic feet in foliage for the cubic feet in roots. This rule of thumb will at least give you a starting place for selecting your pots, cubby holes or troughs.
Once you’ve figured out the size your containers need to be, don’t forget to think about the weight of the wall. At first, it may seem like everything is going fine, but your plants will get larger, and when all that soil gets wet, it gets heavy. After estimating the total cubic feet for the wall, estimate the total weight by multiplying 30-50 lb. per cubic foot. Make sure the wall you intend to build onto can support twice the estimated weight.
The Irrigation System of a Vertical Garden
A regulated irrigation system is a must for an easy-to-maintain living wall. Even when you combine the living wall with a façade, it is critical to provide the right amount of water at the right intervals. When plants are housed in substantially different-sized pots, the amount of water their root systems need varies a lot.
Try to plan a wall with as few different-sized containers as possible. It is not hard to set up a system that can care for two different run times as well as days of the week, but the more variety you have in container sizes, the more complex the watering system. Basically, you may need a separate system for each different size.
Simply allowing the extra water to drain out from the smaller plants is going to cause nutrient deficiencies. The goal for any watering run time is to disperse just enough water to soak the entire root system and not more. A slow-drip system will help distribute the water evenly. Apply the water long enough to get a few drops from the bottom. As the plants mature, the amount and frequency of this water must be increased. A plant receiving lots of direct sun will need more frequent watering than one in shade or partial sun.
The pressure required to supply water to your living wall does not need to be 30-45 lb. as you might think. Drip emitters that are engineered to operate at 30 psi can work at pressures as low as 2 psi. To water an 8-ft.-high wall, a pressure of at least 6 psi will do. The flow rate will vary from manufacturer specs, but the emitter will able to put out nearly 25% of its rated full-pressure flow.
This means you can water your wall from a submersible pump if it is not convenient to add another valve or two to your outdoor irrigation system. If your wall is indoors, the lower pressure will help ensure that connections or emitters won’t pop off and leaks are minimal. The higher you pump the water up, the greater your pressure drop. Flow rates will vary, so pressure-compensated emitters will help.
Dripper lines are a great choice for watering a row of plants, like in a rain gutter set-up. These come with built-in emitters that put out a regulated flow and are spaced 6-12 in. apart. You can use simple ¼-in. tubing with T’s and single emitters as well. A water and nutrient basin can be used with a submersible pump and timer to provide the needed water pressure for your system.
If you do not know much about drip systems, consider consulting an expert. You will still be doing most of the work, but having someone with experience look over your plans can save you a lot of time and money in the long run. Alternatively, hand watering can simplify the irrigation aspect of the design, but there still needs to be good forethought into how and where to apply the water and how the containers will drain.
Figuring out just how and where the excess water will go is a vital part of any successful living wall. Whether you grow your plants in pots, gutters, modified pallets or whatever else you’ve thought of, the water needs to drain somewhere.
If the water can simply drain to the ground, things are simpler, but keep in mind the more water that is drained off to waste, the higher your water costs. Also, many areas of the country have hard water (water with lots of dissolved solids), which will stain. Gutters can simplify your drainage design, as the water drains at one end and can more easily be directed and controlled.
Planning Makes Perfect
The proper amount of soil, the structure to hold that soil, the irrigation design and drainage are all vital elements of a successful living wall. When selecting the plants you want for your wall, consider how each plant type grows. For example, trailing plants could deprive plants beneath them from getting an adequate amount of sunlight.
As with any garden project, planning before you start is imperative, so research thoroughly. Remember that as beautiful and productive as living walls can be, they will also present some problems you may not have dealt with before. Get ready for a fantastic and fun learning adventure!