Contributed by Melissa Muroff
Since the construction of our first green roof in 1997, we have been wringing our hands over our green roof blind spot. Over the years, we worked hard to prove and promote our green roof exceptionalism, but this blind spot left us feeling uncomfortable. Just over two years ago, we decided to face and eradicate the blind spot.
What is this bind spot, you ask? The blind spot is the void of knowledge regarding a green roof’s health following installation and running throughout plant establishment. As a result, we have been consumed with worry over issues ranging from plant diversity, weed pressure, root development, and the impacts of extreme summer heat and prolonged periods of drought. Roofmeadow warranties last 10 to 20 years and include a plant viability guarantee; so, we fret over our blind spot with very good reason.
What was our plan to minimize our blind spot? Developing a means of collecting reliable information from our green roofs and getting that information to the Roofmeadow office for analysis in a timely matter was priority one. Paying for this stewardship commitment was priority two.
Maintenance and Stewardship of a Roofmeadow Green Roof
Roofmeadow was the first company to include an 80% plant coverage requirement at the conclusion of the two year Workmanship Warranty period in our green roof specifications. To achieve that threshold, maintenance is required. Most green roof owners accept that this maintenance is essential; therefore, all we really needed to do was beef up the reporting requirements.
Roofmeadow requires documented maintenance as a condition of the warranty. To facilitate this documentation, we craft a Roofmeadow ® Green Roof Maintenance Manual for all of our projects. The Maintenance Manual includes a Roofmeadow® Maintenance Report which is designed to be completed by the maintenance contractor in the field. A completed Roofmeadow® Maintenance Report includes (among other things) photos and a description of the health of each plant species on the roof.
If you have a penchant for programming, this is where things get exciting. With data from Maintenance Reports pouring in from green roofs all over the country, we developed an information infrastructure capable of processing and storing data in way allows us to better manage our risks and to understand precisely how our green roofs are developing. The Roofmeadow® Plant Database tracks the performance of individual plant species at each maintenance visit. We can cross-reference plant performance characteristics with regional and microclimatic conditions, green roof profiles and plant establishment methods.
Think about it. You make a gamble when developing a green roof plant palette based on text book plant characteristics because most text book information is derived from plant performance on the ground. But green roofs are established in mineralized media which is nothing like native soils, and they are exposed to extreme rooftop weather conditions. Because we couldn’t find a comprehensive repository of rooftop plant behavior, we created one of our own in order to inform our plant palettes and maintenance strategies.
Using the information collected at each maintenance visit, Roofmeadow tracks individual species behavior (including root behavior!), weed pressure, biodiversity, hours required to perform maintenance, the impact of irrigation schedules, media and irrigation water test results, drainage and wind effects.
Documentation of Root Health During a Maintenance Visit
Now, our blind spot is manageable and greatly reduced. What have we learned? Well, for the record – and I can’t overstate this – the need for green roof research is huge. (Calling all universities . . .) Information collected through the Roofmeadow® Maintenance Management Program is helping to fill the industry-wide information void, but we hope that universities invested in green roof research will work to develop the opportunities that we see surfacing as a result of our efforts.
As we watch our green roofs grow up, we have adapted our designs, construction protocols and maintenance stewardship strategies to accommodate the following observations.
1. Foster biodiversity. An un-maintained green roof will lose biodiversity and this is not ok. A green roof supporting one or two plant species is vulnerable to climate changes, pests and media imbalances. Don’t be lulled into thinking that a diverse weed population constitutes suitable biodiversity. Remember, green roofs are extreme environments; many weeds will burn out during summer droughts or winter, leaving large patches of bare media vulnerable to wind scour.
2. Develop a passion for propagating. Expedite plant coverage by spreading cuttings and dividing large plants. Do some homework to learn which sedums are appropriate for propagation via cuttings.
3. All sedums are not created equal. The characteristics of sedum root masses vary. Generally, deep rooted sedums will weather extreme climates better but spread more slowly.
4. Make room for annuals. Although not essential, annual springtime seeding increases biodiversity, nurse-plant environments and, of course, the visual interest of the entire roofscape.
5. Know your weeds. Not all weeds are on a mission of total domination, but for those that are, an aggressive proactive weed management plan will save maintenance dollars later on. Establish maintenance protocols that limit opportunities for weed seeds to hitchhike on to the roof or spread from one roof area to the other. Really, it’s worth the extra time to be careful about this.
6. Embrace your inner chemist. The viability of a green roof depends on the media’s ability to function properly. Submit media and irrigation water samples for annual testing at an accredited laboratory. These results should inform annual fertilization strategies.
7. Take a look under the hood. Get on the roof and make sure that the root systems are thriving and drainage layers are functioning properly. Routinely check the moisture content and the temperature of the media both at the surface and below. Most plants will not survive a swampy roof for long. Shallow, thwarted root masses signal an ecosystem vulnerable to climate extremes.
8. Appreciate the Tao of irrigation. Irrigation requires attention. The “set it and forget it” strategy can get you into trouble. Take the time to calibrate the irrigation in order to minimize water use and create a balanced ecosystem.
9. Look out for unexpected hazards. Be aware that window cleaning fluids and exhaust vent vapors can affect media and plant health. Most window cleaning solutions do not double as fabulous fertilizers. Be mindful of the materials (or creatures!) coming in contact with the green roof and proactively address problems before they create costly complications which can be difficult to remediate.
10. Lastly, enjoy your roof! A well-loved green roof is a well maintained green roof is a healthy green roof.
The Herbaceous Perennial Echinacea ‘Sundown’ on a Pennsylvania Green Roof