Easy grass planting on rooftops with Huang Aiping's Green Carpet

In the landscape design world there is Yu Kongjian, who loves wild grasses. In his design for Zhongshan Qijiang Park he fully showcased the beauty of those forgotten, despised and trampled wild grasses, and the project won the ASLA Honor Award. In the field of roof greening, there is likewise a person obsessed with wild grasses, namely Huang Aiping of Guangzhou Huanggu Decoration Engineering Co., Ltd. He uses wild grasses from rooftops to green roofs, blazing a low-cost, high-benefit trail for roof greening.

Searching high and low for wild grasses

Greening a building is not very difficult; what is difficult is building a scientific and rational green space ecosystem on the roof, letting this system work on its own so as to reduce the labor and materials spent on later maintenance. When he first started doing roof greening, Huang Aiping cultivated natural ground-level grass species. In the early stage of roof greening this was not a big problem, but as time went on, trouble arrived. Because these ground-level grass species are greatly affected by climate, with thick soil and mixed grasses, they are costly and hard to manage, and in winter the soil lies bare, easily causing secondary pollution.

The emergence of this series of problems made Huang Aiping re-examine his path of roof greening: why can't the greening results be maintained? By chance he saw a wild grass on the rooftop, and it suddenly dawned on him——wouldn't selecting grass species from the plants already growing wild on rooftops achieve twice the result with half the effort?

So Huang Aiping began the long journey of searching for and selecting rooftop wild grasses in his career. Through long-term experimental comparison of many wild grass species on rooftops, and under the control of indicators such as ornamental value, stress resistance and root growth patterns, he finally selected a specific grass species——Callisia repens (creeping inchplant). This grass has a long history of growing wild on rooftops in the Jiangnan region, with a green period of more than 300 days. After establishment it can renew and maintain itself. Its root system is weak and fine, rooting shallowly and growing flat; the grass roots interweave with the growing medium in a net-like pattern to form an integral panel, which not only effectively prevents rainwater from washing away the medium, but also carries no risk of roots penetrating the roof waterproof layer. Considering that building a rooftop green space ecosystem requires greater species richness, in addition to Callisia repens, Huang Aiping also selected 6 other plants, all wild plants from rooftops, with the characteristics of tolerating high temperatures, drought and poor soil, and having shallow root systems. "The biggest advantage of selecting from rooftop wild plants is that the finished roof resembles a natural roof, requiring no fertilizer or pesticide, which helps the return of beneficial species such as bees, dragonflies and small birds, and can truly achieve the goal of ecological balance in the living environment," Huang Aiping explained.

Devoted research and development of the "Green Carpet"

Regarding the selection of rooftop plants, although many experts focus their research on screening and configuring plants with strong stress resistance, and some emphasize plant diversity in rooftop lawns, few have studied the wild plant ecosystems of rooftops. On the basis of screening wild grass species, Huang Aiping focused his research and development on building a rooftop green space ecosystem. In 2006 he jointly developed the "natural ecological roof" greening technology with the South China Botanical Garden of the Chinese Academy of Sciences, and in 2008, after upgrading, this technology was further developed into the "Green Carpet" technology.

When talking about the development of the "Green Carpet", Huang Aiping naturally brings up the "band-aid" kept in every household's medicine box, a convenient and effective remedy for treating superficial skin wounds. He hoped to develop a product that would be just as convenient when healing the urban environment damaged by massive construction, simply sticking pre-cultivated grass blankets onto the roof. So, based on the band-aid principle, he began production trials of insulating lawns for buildings. At the company's seedling base in Quannan County, Jiangxi Province, lush grass blankets grow in grid after grid of square frames; this is Huang Aiping's magic weapon for rapidly implementing roof greening——the "Green Carpet". The main grass species used in this grass blanket is Callisia repens, and the medium is only 2 cm thick. Using the principle of wrapping dumplings, the soil is wrapped in the middle with plant medium, and Callisia repens is planted on top; once the grass forms a turf it can be placed on the roof. Because this grass species grows with its roots clinging to the surface layer of the floor slab and creeping along it, without rooting downward, it will not damage the slab layer, so no root barrier layer needs to be laid.

In spring, summer, autumn and winter this grass species displays several colors: green, yellow, red and gray. This is precisely this wild grass species' "authentic performance" in the natural environment, requiring no human intervention or assistance, because it was originally the master of that place.