Algae, liverworts and moss on greenhouses

Green growths such as algae, liverworts and moss can accumulate on the glazing and surfaces of greenhouses, where they are unsightly and cut out light. They can be controlled by improving hygiene and ventilation.

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Algae and moss in a greenhouse. Credit: RHS Advisory

Quick facts

Common name Algae, liverwort, moss
Areas affected Greenhouse glazing and other surfaces
Main causes Damp conditions, poor ventilation
Timing Noticed more in winter, but can be seen after any wet spell

What is the problem?

The build up of moss and algae on greenhouse glazing cuts out precious light from getting to the plants. It can also be problematic on greenhouse flooring and staging. This page considers options for gardeners when lichen, moss and algae are becoming a problem.

Appearance

Algae: A green film or powdery deposit is typical of algae on greenhouse glazing.

Liverworts: Liverworts usually have a green, flattened, plate-like body and no leaves. A common example is Marchantia, which is often topped with umbrella-like sexual organs.

Moss: Moss that grows on glazing bars and on the surface of compost is usually cushion-like.

Cause

Algae, liverworts and moss on internal greenhouse surfaces may indicate a need for increased ventilation and more careful watering.

 

Control

The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.

Cultural control

Where possible, increase ventilation in the greenhouse, especially in winter months.

Water carefully to avoid puddles of standing water.

Thorough greenhouse cleaning should be carried out at least once each year, usually best done in late winter to early spring. Dislodge moss and algae from between glazing panels with a flexible plastic plant label.

Weedkiller control

There are several products available to remove moss and algae from hard surfaces in greenhouses, including the floor, staging and glazing.

  • Jeyes Fluid is suitable for controlling mould and algae on hard surface and disinfecting pots before use 
  • Benzalkonium chloride (Patio Magic, Resolva Xtra Clean or Doff Super Concentrate Path, Patio & Decking Cleaner) kills algae, liverworts and moss on hard surfaces and will inhibit their growth for three to four weeks after application
  • Just Green Glasshouse Cleaner is a surface cleaner (surfactant) based on seaweed extracts is suitable for cleaning all glasshouse surfaces
  • Ecofective Safe to Clean based on surfactants and probiotics can be used to clean any outdoor surface including paving, greenhouses, pots and artificial grass

Inclusion of a weedkiller product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener.

Downloads

Weedkillers for gardeners (Adobe Acrobat pdf document outlining weedkillers available to gardeners; see section 2b)

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