GREEN ROOF PLANTS & RESOURCES
Green Roof Plants
Hardy, drought tolerant plants are best suited for green roof environments because they are more equipped to handle the weather conditions that exist on a roof. These plants are typically native to seashore, alpine, and desert regions and are therefore able to survive in environments often exposed to vast amounts sun, wind, and rain.
The types of plant species Apex Green Roofs uses for green roof installations may vary depending on the type of system, soil depth, and irrigation. Extensive green roofs systems can be planted from cuttings, plugs, or pre-grown mat while intensive systems can have a wide variety of herbaceous species, depending on the type of irrigation system used, the style and design of the roof, etc.
Below are some examples of green roof plants that are often used in living roof environments.
Photos Courtesy of Emory Knoll Farms.
Green Roof Plant Resources:
Green Roof Growth Development
Depending on the system used, green roof plants can take up to year to become fully established. This is why we supply two years of maintenance with our green roof installations so that we can ensure that plant roots have reached a proper depth, check the PH balance of the media, and remove non-planted and/or invasive species.
We have been documenting the development of our green roof projects as they become established, and have provided samples of progressive growth for each planting type in the videos below.
Extensive Green Roof System: Grown From Cuttings
Green Roofs grown from cuttings are essentially started with pieces of plant media (stems and leaves) which are distributed over the surface of the soil during installation. They are held in place by a protective membrane until they become fully established. This protective membrane is much like a net and is typically made of biodegradable material which will eventually disintegrate or be overcome by plants as they grow through and over it. This protective membrane may be need to be more complex in structure when installed on a roof exposed to especially harsh weather conditions.
Green Roofs grown from cuttings are the most affordable green roof systems to install, but they tend need irrigation in the beginning and look the least like green roofs immediately after installation. Growth development within the first year is very gradual in appearance. Three months after installation, plants will begin to push past the protective membrane. After six months, the roof will have 40%-50% coverage. However, after twelve months, a system grown from cuttings will have 80% coverage, which is very similar to the overall coverage achieved using other planting methods over the same period of time.
This method is not recommended for green roof designs which incorporate specific color pattern schemes because cuttings are essentially impossible to create precise color patterns with. In addition, green roofs grown from cuttings can only be planted within a small window of time during the Spring and Fall in order for plants to root properly. Therefore this system may not be ideal for construction projects with uncertain installation schedules.
Extensive Green Roof System: Grown From Plugs
Planting a green roof with plugs is much like planting a typical garden using transplants. Plugs, or pre-grown plants, are installed manually into the soil layer of the roof, usually spaced 6 - 8 inches apart from each other. Since plugs are more mature and established when planted on a green roof, they are capable of rooting more rapidly than a system planted with cuttings, and they also typically need less initial maintenance. Therefore, systems planted with plugs are usually more expensive to install.
Once planted, plugs are held in place by a protective membrane, which may be more structurally complex when installed on a roof exposed to especially harsh weather conditions.
Plugs can technically be planted during any point in the year (depending on weather conditions). Plugs also allow for the greatest design flexibility since plants can be more easily arranged and planted into specific shapes and patterns according to their particular color or growth characteristics. Green roofs grown from plugs appear somewhat sparse immediately after installation. However, plants are visually evident right away. After three months, plants will begin to spread. At six months, 60% coverage is possible. After twelve months, a roof grown from plugs will have 80% - 90% growth coverage.
Extensive Green Roof System: Grown From Pre-Grown Mats
Pre-grown mat systems can be used to help achieve immediate coverage on a green roof, similar to the results found with tray systems. Because they are grown and maintained in nurseries before being installed, they are more expensive to install than green roofs grown from cuttings or plugs, but are more affordable than tray systems. Pre-grown mats can be cut to accommodate certain design schemes on a roof (i.e. curves/sharp angles), but they tend to not have a great variety of plant diversity. Pre-grown mats can usually be obtained for installation anytime after early spring.
Once cut, pre-grown mats need to be installed within 24 hours to maintain plant health; therefore this system requires a precise installation schedule. While full coverage is immediate, plants tend to go into decline immediately after installation of pre-grown mats. The transition from the nursery environment to the roof environment requires plants to adjust to new conditions rapidly, and they require temporary irrigation in the beginning. Once plants have become acclimated to their new environment, they will begin to thrive again.