by Anna Zakrisson on Tuesday, January 11, 2022 updated Tuesday, February 22, 2022
Green roofs can have many purposes, such as stormwater management, heat island mitigation, or simply as a recreational space in an urban asphalt desert. Another fully valid reason is beauty, especially if the roof is clearly visible and relays a message. A well-designed green roof looks good and can be a fantastic marketing investment on top of the potential ecological and financial benefits it brings.
One often requested item for visible roofs and walls is green roof plant color patterns. These patterns are created using different plant palettes and can look spectacular. In this short article, we hope to summarize some pros and cons of such a design decision and discuss the financial and maintenance burden.
Green Roof Color Patterns – A Fight Against Nature
Green roof color patterns can look amazing, but we need to manage expectations; these are living systems, and as the plants grow, develop, and die back, the designs are bound to change unless we put up a big fight against this natural change.
Take, for example, some of these highly structured planting designs from Disney World:
Immediately upon viewing these, you might think, “those are great, but they require a lot of maintenance!”. That is correct. These are striking horticultural displays used in an application where such “magic” is an integral part of the Magic Disney Kingdom. Designers sometimes try to apply some of this magic to green roofs, and we think that is great! But is the intent to maintain the patterns permanently? Or perhaps for just a few years? Either is possible, but the level of effort and corresponding cost must be considered.
The planting design above is an example of the successful use of various colored pre-grown Sedum mats or tiles to create a bit of “magic,” “drama,” and overall visual appeal on a green roof. A standard level of maintenance (i.e., an ecologically focused, cost-efficient maintenance approach) might allow these patterns to evolve into more of a mixed palette over two to five years, such as below:
In most cases, we believe the most appropriate approach is to allow for the natural succession of the green roof vegetation instead of requiring that maintenance crews maintain a rigid geometry. It is a battle with nature. Either is possible, and the decision is primarily a matter of cost (and water accessibility).
Succession: Green Roof Stripes and Patterns Over Time
When a mixed color standard pallet sedum green roof is installed, it generally contains a blend of 15-20 different species of different forms and shapes and growth patterns. One of the reasons for this is to ensure that over time, a stable community will form that naturally and effortlessly (from a human perspective) has been optimized for that specific location and roof. Diversity means resilience, and a resilient green roof means less maintenance and a low risk of costly vegetation crashes.
Over time, the plants that are the best adapted for the specific location (including distinct microclimates on the roof) will outcompete those less adapted. Sometimes this also means fluctuations in community composition within a year. Fast-growing plants with shallow roots, such as ruderal creepers (e.g., Sedum acre, sexangulare, and album), are often the first to “wake up” in early spring before they are taken over by slower-growing perennial plants with deeper root systems (e.g., Sedum spurium John Creech, Immergrünchen, kamtschaticum, floriferum, and Phedimus takesimensis) as the year progresses into the hot summer season.
Learn more about ecological succession in this 6min video!
Do The Patterns Look Good All Through the Year?
Ruderal creepers can double in size within a week at optimal conditions, but they tend to be water sensitive and quickly die back or go dormant when heat and water shortages strike. Still, they are essential for the roof to protect the soil during winter when other plants are completely dormant.
Here we arrive at another design problem: will your color designs look good throughout the year, or will you end up with patches of dead or dormant plants? Some design combinations can look splendid but may require irrigation and a lot of tender loving care. This, of course, comes at a financial and ecological cost that should be transparent already at the design stage.
Even on the same building, it is sometimes possible to see roofs with different dominant species depending on profile depth and sun/shade exposure. Thus, these roofs often have different colors. It is also worth noting that stressed and unstressed plants of the same species sometimes have different colors, as stress can lead to an accumulation of red and orange pigments such as anthocyanins. Hence, stress can also mix up your color palette. There is a lot of work and funds involved in keeping a clean and stable green roof pattern.
I would like to state that I personally think such color patterns can look amazing, and I think they can be an excellent marketing idea, but there must be awareness and honesty of the maintenance required. Another option could be to design patterns and, as natural succession proceeds, view it as natural art. Over the following years, nature slowly paints its own pattern, establishing a stable, beautiful, and resilient roof.
Are interested in learning more about green roof plant selection? Check out these articles on the Purple-Roof blog!