April 5th, 2022 by Sarah Miles

FAQs about the unsightly black marks on your garden’s hard surfaces

Black spots on your patio, drive, and paths of your garden can spoil the whole space, making it look dirty. Here are the most frequently asked questions about these grubby marks.

What are black spots?

Black spots are another name for black lichen, which is a parasitic organism that grows on the surface of stone and concrete.

How do I know if it’s black lichen and not just dirt?

The easiest way to tell whether it’s just dirt is to try and remove a small area by scrubbing it with a brush or similar. If the marks start to lift, then it’s just the general dirt and debris of the garden. If it doesn’t make any difference, it’s likely to be lichen. It is also characterised by its ink spatter-like appearance.

What is black lichen?

Black lichen is a combination of two or three organisms (bacteria/fungi/algae) living in a symbiotic colony. It starts out as tiny microspores that originate from trees and plants and get carried by the wind and settle on hard surfaces, where they feed on the minerals in the stone.

Why is it so hard to remove?

Black lichen has some ingenious self-preservation tactics. Firstly, it sends down tendrils into the stone which allow it to absorb the minerals but also serve to anchor it into the stone itself. It also forms a hard crust over its visible surface which is really hard to penetrate. This is why general cleaning products, abrasive tools (such as brushes or scourers), or high power equipment (such as pressure washers) are ineffective at removing them. In fact, you are more likely to cause damage to the stone.

What happens if you don’t treat it?

If it seems difficult to get rid of, or the spots don’t bother you that much, you may think it’s not worth the hassle of trying to remove it. However, that’s not a good idea. Black lichen thrives in warm, damp conditions and as it exhausts the minerals in one section, it will spread across the surface of the stone seeking out more. It will also deepen its tendrils into the fabric of the stone. This means that it will get progressively worse, looking increasingly unsightly, and also weakening the stone as it deprives it of its minerals.

How do you get rid of it?

Removing black spots is both difficult and easy. Difficult in that you can’t just scrub it away but easy because if you have the right product, there’s very little work involved at all. What you need is a lichen-specific remover, such as Homefront Super Strength Black Spot Destroyer that contains an active ingredient to break down the bonds in the organisms and therefore release their grip.

How do you use black spot remover?

This is where the job becomes very easy. Just apply the product with a watering can or garden sprayer and leave to work. The fizzing action, that breaks it down, will start straight away but leave for around 2-4 hours. Then, simply rinse it away with clean water and allow it to dry. Make sure you do it on a dry day (as any moisture will just dilute it) and keep animals and children away from it while it’s working.

Will black spot remover also clean the patio?

Yes, this is an added bonus. The black spot remover will also clean away any stubborn dirt and grime as well as green mould and algae, leaving your patio like new.