Is moss good for roofs, and is roof moss good for the garden?
Short answer. No, moss is not good for a shingle roof: it holds water against the shingles, lifts their edges and speeds up rot and granule loss. Untreated moss can be reused in a damp, shady garden, but moss that has been treated with roof chemicals should not be.
The myths
- "It insulates the roof." Any insulating effect is trivial compared with your attic insulation, and wet moss holds heat and moisture where you do not want it.
- "It is like a green roof." Real green roofs are built on waterproof membranes designed to stay wet. Asphalt shingles are designed to shed water and dry out quickly.
- "It protects shingles from sun." It also keeps them damp, and dampness does more damage than sun in a humid climate.
What moss actually does to shingles
Moss grows in the gaps between shingle courses, wicks water up under the laps, and slowly pries the edges upward. That exposes nails and the layer below, lets wind catch the edges, and keeps decking damp. On wood shake roofs, it accelerates rot even faster. See moss and lichen on roofs.
Using roof moss in the garden
- Only use moss that has not been treated with zinc, bleach or other chemicals.
- Moss transplants best to spots that match where it grew: shaded, damp, and on firm soil or stone.
- Do not climb onto a roof to harvest it. Collect what falls naturally or what you can safely reach from a ladder at the eave.
Where moss belongs
On shady ground in a Georgia garden, moss is a great low maintenance ground cover. On your roof, it is a slow leak in progress. For prevention, see trees and your roof.