Algae vs. Lichens in the Garden: Friend, Foe, or Feature?

Green slime on paths? Crusty patches on stone? Before you scrub, know what you're looking at—and whether to remove or encourage it.

Algae: The Basics

Non-flowering, stemless plants. In greenhouses/polytunnels, winter buildup on glass reduces light. Fix: trim surrounding vegetation, ventilate daily, wipe with mild detergent (glass) or soapy water (plastic).

On paths and steps, algae + moss create slip hazards in damp shade. Reduce shade → more sun → less moisture. Traditional control: copper sulphate (bluestone), 10 g/10 L water, applied dry, brushed in, left 3 weeks, then stiff-brushed. PPE required. Avoid drift to plants/lawns.

Lichens: Algae + Fungus in Symbiosis

When algae and fungi partner, you get lichens—tough, slow-growing, pollution-sensitive. They colonize gravestones, boundary walls, terracotta pots, rock features. White crusts with yellow/orange splashes = common lichens. They indicate clean air.

Encouraging Lichens (Yes, Really)

For character on stone, sculptures, or pots: make "lichen slurry"—1 tbsp ground lichen + 1 pint natural yogurt or buttermilk. Paint/dab on target surface. Wait. Lichens grow slowly, but the patina is authentic and enduring.

Verdict

• Algae on paths: Safety hazard → manage.
• Algae in greenhouses: Light thief → clean.
• Lichens on hardscape: Character, air-quality indicator → welcome.

Not all green growth is equal. Identify, then decide.