The green roofing industry has very specific taste when it comes to the plants they use on roofing projects. Plants chosen need to be able to deal with the harsh conditions that metropolitan rooftops have to offer. They need to be shade tolerant, drought resistant, and have a shallow root depth so as to deal with small amounts of growing medium. They also must have a large amount of biomass in their leaves to allow for better thermal insulation. The genus of Sedum is the heavyweight champion of these traits, which is becoming more and more prevalent in the city as the green roofing industry flourishes.
Sedum contains over 400 different species of plants and is able to adapt to arid climates and soil conditions. They are extremely resilient, and recover quickly after having received a small amount of water. Sedum has a modified metabolism, which helps it grow in desert like conditions. At night the plant’s stomata absorb carbon dioxide and turn it into malic acid, which is used during the day for photosynthesis. The stomata in the leaves only open at night, to minimize moisture loss during really hot days. Most species in this genus have a waxy layer on their leaflets, which prevent them from being burned or harmed by the suns rays. Sedums are succulent plants, meaning they store water in their leaves and stems, just like Aloe vera. Water, having a very high specific heat, is not prone to temperature change, and therefore provides for a perfect thermal insulation layer on rooftops. This means that during the summer, the suns rays are absorbed by the Sedum plants rather than radiating into the roof. This same concept applies during the winter; since Sedum plants are green year round, they help limit heat loss through the roof in colder months.
Sedum also has a very shallow rooting depth and can flourish in a setting with a limited of growing medium. Not all Sedum plants are great for green roofs; species that grow in blankets rather than upwards are better for insulation layers. There are very little incidents of species in this genus having issues with disease or insect infestation, which is a major plus for the green roofing industry. Without sedum, a good amount of people would be very unhappy. Let’s continue to cover NYC rooftops with this awesome plant!
- Christian Hill