When the moss roof on the springhouse shown below and to the right was planted two years ago, a mixture of 75% Hypnum imponens and 25% Dicranum scoparium fragments was used, inviting friendly competition between the two species. However, this moss-friendly environment of moisture-holding aggregate and water-retention gel created a landing zone for spores of many other moss species. Now, there are at least 12 species of mosses on the roof, of which Thuidium delicatulum (Fern Moss) is predominant.
According to Dr. Robin Kimmerer, there are millions of microscopic moss spores floating through the air at any time. All they need is a moist place to land and start growing. The micro-crevices of roofing media create the perfect, moist spot where spores can germinate happily.A German green roof specialist who has seen green roofs in Europe mature over the last 20 years recently opined that eventually all green roofs will turn to moss. We’re not so sure about this, because mosses, which are tiny and non-vascular, cannot outcompete the larger, vascular plants. However, for a shade roof this may be true. So few plants survive in shade, whereas mosses are ideally suited for it. Perhaps this is the environment where mosses can eventually outcompete the vascular plants.
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| Thuidium delicatulum, Hypnum imponens, Bryum cf. capillare, Plagiomnium cuspidatum, Dicranum scoparium and Ceratodon purpureus are some of the mosses that have settled in to populate the roof of this springhouse. Image by Keith Bowman. |
- Is lightweight
- Retains ten times its weight in water
- Thrives in shade produced by building shadows
- Is drought tolerant once established
- Grows rapidly — three to six months for full coverage
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