Slippery paths and steps covered in algae-like growths, liverworts, lichens and moss are hazardous. Winter is traditionally the time when algal, moss and liverwort growth is most significant, but build-up can occur during any wet period or in shady, humid areas.
On stone and timber features lichens and moss can be very attractive and give a mature look to the garden. Such growths do not harm the surfaces on which they grow, and are a natural part of the garden ecosystem.
Where growths of algae, moss, lichens and liverworts present no hazard, such as on stone sculptures and features, gardeners are encouraged to allow them to flourish. Their appearance signifies a mature garden, blends in harsh stonework to the environment, and adds to the biodiversity of the garden. Indeed, in rural areas it is possible that gardens could harbour very rare species of lichen.
For areas where growths are a slip-hazard or are contributing to the weathering of wooden structures, the following controls are recommended.
Dislodge moss from between paving by running a sharp knife along the cracks. Alternatively, use a block paving brush with a long handle, narrow head and wire bristles for effective cleaning without stooping
A pressure washer will remove moss and algae effectively. However, use this method with care in areas where drainage is unsatisfactory as the extra water could exacerbate damp problems. Always wear goggles when using a pressure washer. This is the best method for removal of moss and algae from wooden garden features. After spraying, consider treating fences and sheds with wood preservatives and garden furniture with teak oil
Brush hard surfaces with a stiff broom on a regular basis to help prevent growths from taking hold. Raking loose surfaces such as gravel helps to keep these areas free of both moss and weeds
Prune overhanging plants to improve air flow – this will allow the drying effects of sun and wind to reach the site.
Ensure surfaces slope slightly to prevent standing water
Improving drainage in the surrounding area will also help to deter growths. Dig out shallow channels along the edges of paths, patios and drives and fill with coarse gravel to absorb run off water
Fork over beds close to damp surfaces to maximise drainage and water absorption
Only pave areas essential for access. Choose permeable paving when constructing new hard surfaces and keep drains clear of leaves and debris
Surface finishes that are raised to give grip in wet weather are ideal for shady spots. On wooden surfaces try tacking down some chicken wire as this too will make it less slippery. Spreading coarse sand over garden steps is another simple anti-slip solution
Algae, moss, lichens and liverworts can be removed with most proprietary patio cleaners. Most products are non-persistent and repeat applications will be required.
Use products based on benzalkonium chloride, pelargonic acid, acetic acid or nitrilo triacetic acid/trisodium salt which claim to control moss and algae on hard surfaces or natural paths. They may also give some control of lichens
Just Patio and Concrete Cleaner is a natural surfactant (detergent) based on seaweed extracts and should be especially safe to use near planted areas. It claims to remove algae on hard surfaces
Path and patio cleaners based on hydrochloric acid or bleach have some effect but are not recommended for use near plants. They can also discolour certain types of stone