Should You Use 4 or 6 Inch Plants in a Living Green Wall?
Are 4″ or 6″ plants better for living walls? Why do most living green wall systems use 4″ plants?
On a few occasions, I’ve been asked by interiorscapers something along the lines of “when are you going to come out with a living wall system for 6″ plants?”. I’ve thoughtfully considered the idea and I wanted to share my findings here in order to help educate the interiorscape community on this topic.
There are a few key variables to consider when you think about the effect of plant size choice for a living wall system. These are useful things to consider when comparing different living wall systems, planning a living wall installation, or, in my case, considering whether to expand your product line.
This seems obvious, but so many interiorscapers have an “ah ha” moment when I raise this issue that I think it bears repeating. A 6″ plant has a much larger root ball than a 4″ plant. That isn’t much of a problem when you put them into a pot and sit them on the floor, but it does become an issue when you start hanging them on a wall. The bigger the root ball, the more the plant has to stick out from the wall, the more the plant weighs, and the more water it drinks. In general, systems that use 4″ plant material will be slimmer, lighter, and use less water than those systems that use 6″ material. The slim profile makes the wall more attractive from a side angle, but more importantly, the depth of the wall can also make a difference with ADA compliance, as I outlined in a previous post.
A big living wall installation can require hundreds of plants. For example, a 500 square foot Suite Plants LivePanel living wall will require approximately 2,250 4″ plants. If you opt for 6″ vs 4″ plants — while you’ll need fewer plants — the price can be one and a half to two times more. So when you’re buying thousands of plants for a green wall, those few dollars of price difference between 4″ and 6″ plants can add up. Also, don’t forget the difference in future plant replacement and maintenance costs.
This is one area where I used to believe that 6″ plants held an advantage. My logic was that even if you had poor quality plants, all else equal, the larger plant had more time to grow and mature and would thus be more equipped to handle the stress of being planted on a vertical wall. Well, I was wrong. Some helpful advice from Dave Winter of Midwest Tropicals helped to set me straight:
“From a plant growth standpoint a 4” plant would be preferred because they are physiologically younger and better able to adapt to the unique environmental challenges of a living wall. A younger plant is more flexible and able to reorient itself to the challenges of the vertical landscape. The 4” plant will suffer less stress and therefore have a head start on producing new growth. A larger, more mature plant is more likely to suffer stress as its older root ball is manipulated and possibly damaged fitting it into the wall system. The use of 4” plants will probably produce a better end result with less potential replacements due to dye back or mortality. As a horticulturist I prefer a 4” based living wall system for this reason.”
Now, on the related topic of quality, it’s just a matter of finding the right supplier. I would venture a guess that most interiorscapers don’t like working with 4″ plants, but I can’t blame them when I see the poor quality of the 4″ plants that some growers ship. I think that some growers speed up their turnover in an attempt to increase profits and end up shipping out underdeveloped 4″ plants. There is a big difference between a quality 4″ plant and an underdeveloped 4″ plant. Just remember that not all 4″ plants are created equal and do yourself a big favor by finding a high quality 4″ plant supplier.
Do interiorscapers believe that there is a wider selection of 6″ plants in comparison to 4″ plants? I don’t know for sure, but I do get the feeling that since interiorscapers use 6″ plants more frequently they have a familiarity preference for them over 4″ plants. However, there is probably a greater amount of variety in 4” plants, partly due to the number of growers specializing in the mass market and partly due to the fact that many dwarf plant varieties will come to a near mature state in a 4” pot, whereas they would not be sizable enough to sell in a 6” pot. You might have to shop around a little more than you’re used to and order from some different suppliers, but there is plenty of 4″ plant material out there. In fact, I have even herd of some growers that have special varieties meant for living walls. Most interioscapers are accustomed to working with at least 6″ size plants, but in order to be a green wall guru you’ll have to become more comfortable with using 4″ material.
In closing, I’ll again reference the wisdom of Dave Winter:
“I can understand that installers might prefer to start with a larger plant because they believe it will give them a “fuller” living wall. However, a properly designed system will provide an equally full looking end result whether it is based on 4” or 6” plants. With any vertical garden one of the prime challenges, of course, is supplying water. A smaller plant requires less water and is less likely to undergo wilting or water stress. Smaller, younger plants are also more able to adapt over time to the water feed rate of the particular living wall system.”
I owe a big thank you to Dave Winter at Midwest Tropicals for taking time to review my first draft of this post and provide feedback based on his 40 years of experience as a foliage buyer, grower, and Horticulture teacher.