July 24th, 2019 by Chris Chapman

Ever had a stubborn spot on your patio that you just can’t clean off? There’s a good chance you were dealing with lichen! Lichens cause black or green spots to appear on almost any surface, and they can quickly overwhelm patios and paving. But what are these stubborn black spots, and how can you get rid of them? This guide will explain all you need to know!

What is Lichen?

The reason lichen is so tricky to get rid of is that it isn’t actually one organism, it’s two. What we call lichens are made up of a combination of bacteria or algae and (sometimes several species of) fungi. The bacteria provide food for the fungi, while the plant-like structure of the fungi traps moisture and nutrients for the bacteria. This process is called symbiosis – when two different life forms work together to benefit one another. As a result of this, lichens can grow very quickly. Their colour and texture can vary depending on the type of fungi they’re made up of. Some are furry-looking, while others seem to be crustier in texture. Some might be a dusky orange colour, while many are various shades of green. The most common one you’ll find in your garden, though, is the infamous black spot.

Black Spot Lichen

This variety of lichen appears to be almost flat and is dark-grey-to-black in colour. It thrives on patio and paving slabs as the fungi spores penetrate beneath the surface of the paving, acting as a sort of anchor. This makes them nearly impossible to get rid of through normal means. If you’re thinking of using a weed killer, don’t! Lichens are very resistant to most weed killers. In fact, some weed killers can actually increase lichen growth! Many weed killers contain ingredients like glyphosate, which break down very quickly. When these ingredients break down, the lichen can absorb them and use them as food to super-charge their growth.

How to Get Rid of Lichen

Lichens are extremely tough to get rid of, so you'll need some specialist cleaning supplies to do the job. Look for a patio cleaner that contains sodium hypochlorite, also known as dairy bleach. This stuff is stronger than regular bleach, but it's still safe once it's rinsed and dried, meaning it’s commonly used in farming (which is where it gets the name). Pro-Kleen’s Black Spot Remover and Patio and Driveway Cleaner both contain this magic ingredient. It breaks down both the fungi and the bacteria that need each other to survive, meaning you can simply rinse and scrub the lichen away. Just spray or water your solution onto the lichen and leave it to dry. Bear in mind that this solution will kill plants, so if the affected area is right next to a lawn or flowerbed we recommend that you use a trigger spray. This will allow you to be more accurate when applying the black spot remover. You should also avoid applying when rain is forecast – the last thing you want is for a rainstorm to wash all your hard work away! You should leave the solution on your patio for a minimum of 2 hours. For best results, leave it overnight. If you have children or pets, keep them off the area during this time. After this, rinse off the area and leave it to dry. Once dried, it’s perfectly safe to allow children and pets onto the area again.

Re-Treating the Area

Even with this super-strength lichen remover, you might still need to use several treatments before your lichen problem is completely gone. Don’t worry, this is perfectly normal! Lichen has been around for hundreds of millions of years, so getting rid of it can sometimes need a bit of extra persistence. Just re-treat the area a few days after your initial treatment and keep chipping away at it until it’s gone.

What Surfaces Can I Use Lichen Remover On?

Sodium hypochlorite is a bleach, but it’s largely safe to use on most hard surfaces. You can safely use it on concrete, granite, terracotta, metal, white porcelain, Indian sandstone, travertine stone and other non-porous rocks. Be warned, though, that it isn’t suitable for use on porous or painted surfaces as it can cause discolouration. That means you shouldn’t use it on PVC, coloured porcelain, tarmac, fencing, or decking. If you need to remove lichens from these surfaces, you should use a concentrated bleach-free moss remover like Ultima Plus XP. This isn’t as strong as Pro-Kleen’s Black Spot Remover or Patio and Driveway Cleaner, but it’s the strongest patio cleaner you’ll find that doesn’t have bleach in it. It might take a few more treatments and a bit of scrubbing, but it can remove lichen from wood, decking, and PVC.

Lichen Facts

It might not seem like it, but lichen can be quite interesting when it’s not ruining your patio!

• Around 6% of the Earth’s surface is thought to be covered in lichens. No wonder they always end up on your patio!
• Lichen has one of the longest lifespans of any living thing on Earth. Some of it has been aged at 8,600 years old!
• Lichen can survive anywhere on Earth – even in the arctic. This is why getting rid of it is easier said than done!
• Some lichens have been used as dyes for centuries. The famous Harris Tweed fabric is still dyed with lichens to this day.
• Some lichens are actually edible! That doesn’t mean you should just scrape up any that you find, though – only a select few types are edible and they have to be boiled, cleaned, and roasted first.