Lichens

Lichens are non-parasitic, plant-like organisms; they are, in fact, composite organisms – a species of fungus growing with a species of algae and there are nearly 2,000 species of lichen in the UK.

Lichens prefer areas with clean air and moist or damp conditions – although they will also grow in much drier conditions.

They colonise the bark of trees and shrubs, as well as fences and other wooden structures, rocks and even paving slabs. They do not harm the plants they grow on – although some people think they are a disease. But because they more commonly grow on plants that are already stressed, weak or lack vigour, many people think they are the cause of the problem.

While they can look attractive, and are often encouraged on hard surfaces to help age and even improve their overall appeal, or as part of Japanese gardens, on paths and patios they can become slip hazards.

• Beds
• Borders
• Hard surfaces
• Plant stems and branches
• Lawns

Depending on species, lichens can be silvery, grey, green, yellow or orangey in colour. They can be divided into three main types.

Leaf-like (foliose) lichens are flat and creep over the substrate they are growing on.

Bush-like (fruticose) grow above the substrate, either upright or pendulous.

Crust-like (crustose) lichens look like thin, flat crusts, and mainly grow on paving and wood.

In lawns, dog lichens (Peltigera) are the commonest. They are grey or brown, made from soft – almost jelly-like at first – flat, lobed structures. They tend to grow in the same conditions that encourage moss in lawns.

There are numerous ways to control lichens, mainly depending on where they are in the garden. Or, they can be left alone, if their presence improves the overall appearance of the structure they’re growing on.

On plants

You could try to physically remove the lichen, but this should be avoided, as it would probably do more damage to the bark and branches.

Lichens can be controlled to some extent by improving air circulation around and through the plant – prune out any overcrowded branches – especially old branches –and remove overhanging branches from other plants and any vegetation growing around the base of the plant.

Improve the overall growing conditions for the plant to increase its strength. Look at the condition of the soil and whether it becomes too dry in summer or overly wet or waterlogged. Ensuring conditions for good root growth will help to increase the plant’s vigour. Water if and when necessary, mulch the soil and feed annually in spring with a granular fertiliser. Applying a foliar feed, especially of a seaweed-based tonic, may help to improve strength and vigour.

On hard surfaces

Lichens can usually be controlled by physical removal, such as with a scrubbing brush or wire brush, or use a pressure washer – although this might just spread them further!

On lawns

Use the same methods as for moss control.

On the soil

Lichens sometimes grow on soil, which is a sign that the soil is compact, airless, may contain too little organic matter and remains moist for much of the year. It is usually only a problem on heavy clay soils.

The lichen can be scrapped off, but it will return unless something is done to improve the compaction and drainage of the soil. Dig over the soil and dig in bulky organic matter and even sharp sand and/or horticultural grit.

On plants

There are no chemical controls for controlling lichens growing on plants.

Using a winter wash, may have some effect at reducing their growth.

On hard surfaces

Numerous hard surface cleaners are available, which should control lichens. Many are simply watered on and left to work, with no scrubbing or hard work needed.

On lawns

Use the same methods as for moss control.

It’s pretty difficult to prevent lichens arriving in your garden in the first place. If the conditions are correct, they will just appear!

• Hand forks
• Fertilisers
• Secateurs
• Hard surface cleaners