Lichen
Lichenes
Lichen is a slow-growing crust of algae and fungi that colonises thin turf, garden beds, paths and tree bark, usually signalling low vigour rather than causing direct harm.
Lichen is not a single plant but a partnership between a fungus and an alga (or cyanobacterium) living together as one organism. The fungus provides structure and anchors the lichen to a surface, while the alga photosynthesises and supplies food. Because it isn't a true weed or a plant pathogen, it doesn't feed on your turf or garden plants directly.
On turf, lichen typically appears as flat, greyish-green to blue-green or almost black crusty or scaly patches sitting on top of the soil or thatch surface, often in thin, bare or compacted areas. It can also form on garden mulch, pavers, retaining walls, rocks and the bark of trees and shrubs, where it shows up as crusty (crustose), leafy (foliose) or shrubby, branching (fruticose) growths a few millimetres to several centimetres across. Growth is slow, often taking months to years to establish and spread.
Lichen is common across Australia in gardens, lawns and bushland, and becomes more noticeable during cool, damp weather in autumn, winter and spring when moisture is reliable and competing plant growth slows. It's especially prevalent in shaded, poorly drained or compacted areas where turf grass is struggling, since lichen tolerates conditions that grass finds difficult.
Management focuses on improving the growing conditions for turf or plants rather than attacking the lichen itself, since it isn't parasitic and won't kill healthy, vigorous plants or grass. Improving drainage, reducing compaction through aeration, increasing sunlight penetration by pruning overhanging branches, and correcting mowing height and fertility practices will help turf outcompete lichen over time. On bark, lichen is generally harmless to tree health and doesn't need to be removed unless it's a sign of overall tree decline from other causes.
How to identify
- Flat, crusty, scaly or leaf-like growths in shades of grey-green, blue-green, yellow-green or black on the soil surface, thatch, mulch, bark, pavers or rocks
- Growths are dry and brittle when dry, but swell and become slightly rubbery or slimy after rain or watering
- Most common in thin, bare, shaded, compacted or poorly draining areas of lawn where grass cover is sparse
- Slow to spread — patches enlarge gradually over months rather than appearing suddenly
- Simple field check: lichen sits on top of the soil or thatch rather than rooting into it, and can usually be lifted or scraped off the surface with a hand or trowel, unlike moss which has fine root-like rhizoids anchoring it, or algae, which forms a slimy green film rather than a crusty or leafy structure
- Lookalike — moss: moss is a true plant with tiny leaves and forms a soft, dense green mat; lichen is typically crustier, drier when dry, and often greyer or more multicoloured
- Lookalike — algae: algae forms a slimy, slippery green-black film on wet soil or turf surfaces, especially after heavy rain, whereas lichen has a more textured, crusty or scaly structure even when damp
