Remove Lichen From Retaining Walls With These Garden Tools

Lichen can add character to ancient stone and a little biodiversity to a garden, but if it's taking over your retaining walls, you may find the result can be somewhat unsightly. As a result, you may want to find a simple solution or garden tool(s) that can help you to remove it. Fortunately, all you need to get the job done is a bottle of bleach, water from the tap, and a few tools, like a pump sprayer and a stiff brush. You'll also want a hose with a jet nozzle, or even grab the pressure washer if you have one.

Lichens are living organisms that cause white, greenish-gray, brown, or even yellow patches on the surface of stone, bricks, and other hardscaping materials (unlike moss, lichen is rarely green when it's dry). They're a mixture of algae and fungi, and may degrade the surface of your retaining wall material over time. So, if you're a homeowner who decided to ditch the concrete and build your retaining wall using natural stone, chances are you'll be dealing with a lichen growth problem, eventually.

When you do, or if you already are, you can apply this homemade solution. Note that the bleach solution will effectively kill the lichen. Then, you will just need to use a bit of elbow grease and your stiff garden brush to remove the dead organisms from the stone or brick.

Since you're going to use household bleach, which only contains around 4.5% sodium hypochlorite, you can mix up a 1:1 mixture. However, if you're opting for industrial sodium hypochlorite with a 10% to 15% concentration, only use 1 part bleach and mix it with 4 to 5 parts water.

It's important to note that you should always add the bleach to the water and not the other way around to avoid any corrosive splashes. Also, make sure you wear protective clothing, eyewear, and a mask when you're working with bleach.

Once you have your bleach solution in your sprayer, you want to spray the lichen-affected areas on your retaining wall liberally so that you get good coverage. Just like you need to think twice before using bleach to kill weeds in your garden, keep in mind that the solution will also damage any other growth it comes into contact with, so avoid any overspray onto surrounding garden areas. Give the solution around 15 to 30 minutes to do its job, and then scrub the affected parts of the retaining wall with the stiff brush to dislodge as much of the lichen as possible.

Finally, rinse off the remaining bleach solution – taking extra care so that the runoff doesn't end up on garden beds or lawn areas. If the lichen has been on the surface for some time, and the first application does not remove all of it, repeat the process. (On a related note, learn what those dark stains are on your roof — they aren't dirt.)