How to Remove Black Spot Lichen

You’ve probably noticed them. Those stubborn black circular spots that appear on your patio, driveway, or garden walls and absolutely refuse to budge. You’ve tried scrubbing. You’ve tried the pressure washer. They’re still there, mocking you.

Welcome to black spot lichen. It’s one of the most frustrating growths to deal with in UK gardens, and it’s far more common than most people realise.

What Actually Is Black Spot Lichen?

Despite what many people assume, black spot lichen isn’t moss, mould, or algae. It’s something else entirely.

Lichen is actually two organisms living together: a fungus and either algae or cyanobacteria. They exist in a symbiotic relationship, with the fungus providing structure and protection while the algae provides food through photosynthesis. This partnership makes lichen incredibly tough and resilient.

The black spots you see on paving are typically a type called crustose lichen. It grows flat against the surface and bonds incredibly tightly to the stone. Unlike moss, which sits on top of surfaces, lichen actually penetrates into the pores of the material it’s growing on. This is why it’s so hard to remove.

Why Black Spot Lichen Is So Difficult

If you’ve tried to remove black spot lichen and failed, you’re not alone. There are a few reasons it’s such a nightmare:

The bonding is physical, not just surface level. Lichen sends tiny root-like structures (called hyphae) into the stone itself. Scrubbing the surface doesn’t touch these anchoring structures, so the lichen just grows back.

Lichen has a protective outer layer. This waxy coating repels water and many cleaning products, which is why a quick spray of household cleaner does nothing.

It’s extremely slow growing but extremely persistent. Black spot lichen might only grow a few millimetres per year, but it can live for decades. Those spots on your patio could be older than your house.

What Doesn’t Work

Let’s save you some time and frustration. These common approaches won’t get rid of black spot lichen:

Pressure washing alone rarely works. You might blast off the surface layer, but the lichen regrows from the structures embedded in the stone. Some people pressure wash the same spots year after year without ever solving the problem. You can also damage softer stones like sandstone or limestone with high pressure.

Scrubbing with a wire brush is similarly ineffective. You’ll wear yourself out and potentially damage the stone surface, but the lichen will return.

Household bleach has mixed results. It might lighten the colour temporarily but rarely kills the lichen completely. It can also damage plants, discolour stone, and isn’t great for the environment.

Vinegar and other weak acids struggle to penetrate the lichen’s protective layer. They work better on moss and algae than on established lichen.

What Actually Works

The key to removing black spot lichen is using a treatment specifically designed to penetrate that protective outer layer and kill the organism throughout its structure.

Here’s the process that actually gets results:

Start by applying a lichen-killing treatment to the affected areas. Use a pump sprayer for even coverage and make sure you thoroughly wet each lichen spot. The treatment needs time to penetrate, so don’t rinse it off.

Be patient. Unlike moss, which dies within days of treatment, lichen takes longer to respond. You might not see obvious changes for two to four weeks. The lichen will gradually change colour, often going grey or brown, as it dies.

Once the lichen is properly dead, it releases its grip on the stone. At this point, you can remove it much more easily. A stiff brush, plastic scraper, or even a pressure washer will now lift off what previously seemed impossible to shift.

For heavy infestations, you may need a second treatment. Apply, wait, and remove again. It takes longer than dealing with moss, but it works.

Treating Different Surfaces

Black spot lichen appears on various surfaces around the garden. The treatment approach is similar, but there are some considerations for different materials.

On Indian sandstone and natural stone, be cautious with scraping tools. These softer stones can be scratched or damaged. Use a plastic scraper rather than metal, and avoid aggressive wire brushes.

On concrete and block paving, you can be a bit more robust with removal methods once the lichen is dead. These harder surfaces tolerate more aggressive cleaning.

On rendered walls, treat carefully and avoid any scraping that could damage the render surface. Let the treatment do the work and use only a soft brush for removal.

Preventing Lichen From Returning

Once you’ve put in the effort to remove black spot lichen, you’ll want to keep it away. Complete prevention is difficult (lichen spores are everywhere), but you can slow regrowth significantly.

Improving airflow and sunlight helps. Lichen, like moss, prefers damp, shaded conditions. Cutting back overhanging plants and ensuring good drainage makes your paving less hospitable.

Regular maintenance treatments work well. Applying a moss and lichen killer once or twice a year, even when you can’t see obvious growth, prevents lichen from re-establishing. This is much easier than dealing with another heavy infestation.

Keeping surfaces clean reduces the organic matter that lichen feeds on. Sweep away leaves, clear debris, and don’t let soil or mulch build up against paving edges.

Our full guide to moss, mould and algae removal covers prevention strategies that work equally well for lichen.

Black Spot vs Other Growths

Sometimes what looks like black spot lichen is actually something else. Here’s how to tell the difference:

Black spot lichen forms distinct circular patches, typically 5-50mm across. The edges are usually well-defined and the surface has a slightly crusty texture. It’s firmly attached and won’t brush off easily.

Black algae tends to form more irregular patches or streaks. It’s often slightly slimy when wet and comes off more easily than lichen.

Moss is green and cushion-like. Even when dried out and dark, it has a different texture to lichen and sits on top of surfaces rather than bonding to them.

Understanding what you’re dealing with helps you choose the right treatment approach.

Is Lichen Harmful?

Black spot lichen won’t damage most hard surfaces. It’s mainly a cosmetic issue. However, on softer stones like limestone, the acids produced by lichen can cause very gradual surface erosion over many years.

The bigger concern for most people is simply that it looks terrible. A patio covered in black spots isn’t inviting, and it can make your outdoor space look neglected even when you’ve tried hard to keep on top of it.

Ready to finally get rid of those black spots? Stop wasting time on methods that don’t work. Our Moss, Mould & Algae Killer penetrates lichen’s protective layer and kills it properly, so you can actually remove it.