Moss is infuriatingly difficult to control. Once it anchors onto concrete, it does not go away without a strong fight.
The only way to keep moss from growing on concrete is to reduce the moisture content that attracts it.
Without treating the source of the problem, repeat treatments with various moss removal methods will only offer temporary fixes.
The moss will always return. Even chemical treatments will not keep it away. It will keep it at bay for a while, but it will eventually return.
The cause is excess moisture, lack of sunlight, and ultimately damp ground conditions.
How to keep moss from growing on concrete
To keep moss off of concrete, moisture levels need to be lowered. That can be done by sealing concrete, cutting bigger plants back to expose the ground to sunlight – nature’s ground drier. Hardscaping around lawns may be required to stop water run-off raising the moisture level under concrete.
1. Seal concrete to lock the moisture out
Concrete is porous. If it is not sealed, water pours through it into the soil and the builder sand beneath it.
The same materials concrete has, and the soil and sand it is laid on is how gardeners and fish keepers grow moss. Look into how to grow moss in a terrarium and you will see that your driveway or concrete paths are just moss breeding grounds on a bigger scale.
To stop moss growing on concrete, those conditions need to be changed.
Outdoors, the substrate quality of concrete and base layer it is laid on provides the climate moss seeks out to anchor onto.
Concrete can hold a tremendous amount of moisture. That is why it should be sealed, and re-sealed every two to five years.
Without sealing concrete, water soaks through it, the concrete remains moist, and once winter rolls around, water inside the concrete freezes, expands, and then the concrete cracks.
Those cracks increase air circulation making it even more of a breeding ground for moss.
Sealing the concrete is how to lock out moisture to prevent moss spores from settling and germinating.
Moss needs moisture more than it needs heat. Lockout the moisture, it will not return.
Only use slip-resistant sealers
The only thing to be careful with when coating concrete in a sealer is that it is slip-resistant.
Some acrylic sealers have no additives to make them anti-slip.
The result can be a concrete driveway, path, or paved patio that becomes just as slippery when wet as it was when the moss was covering it.
The solution for that is to either mix in an anti-slip additive or use a specialty penetrating sealer.
The difference between acrylic and penetrative concrete sealers
Acrylic sealers cause water to bead on top of the concrete, then either run-off in a drainage border, drain, or evaporate.
Penetrating sealers create a barrier within the concrete, rather than on top of it.
There will still be some moisture in concrete with this type, but it will not be able to seep through to the ground under it.
Either sealant works to reduce moisture in the concrete.
2. Improve Drainage
The longer water stays on the concrete, the more water seeps into it and under it.
This is the reason concrete is installed with a gradient. Every concrete installation and even turfed lawns are installed with a slope. If they did not, the ground would flood.
On roads, the gradient is usually 0.5% at least to allow for water run-off. If it were not for that gradient, vehicles would be forever skidding on wet roads.
In gardens, the gradient is higher and is based on the material. Concrete pavers should have a 1% slope and turf; a 2% slope. Those are minimums.
Should you have the gradients correct but still find water pooling on the concrete, it will either need the gradient increased or additional drainage installed.
The fastest method to fix water pooling on concrete is to install an additional drain, but that can be costly. It is not the type of home improvement job done just to keep moss from growing.
Consider doing this if the drainage is so poor that it risks structural damage. Such as water pooling too close to your home.
Alternative quick wins for drainage problems are to make sure water drains away from where moss is growing, or at least into a sunny spot where water can evaporate quicker.
Cutting overhead branches can open driveways and paved patios up to sunlight, helping it dry faster after rain.
Check downpipes are draining water into the most suitable spots in your yard (closest to drains) and that guttering is not leaking water before it reaches the downpipe.
Garden sheds can also be problematic as those are designed for water to run away from the roof onto the ground.
If you have a concrete base wider than the shed, the guttering should be installed along the roof ridges of the shed, and perhaps a rainwater barrel connected to it to prevent rainwater saturating concrete around a shed.
Keep in mind that when using border plants or edging plants, the ideal soil to compost ratio is only 30% maximum of compost.
Too much can alter the moisture capacity of soil causing excess water to back up onto the concrete that it came from. If it cannot drain, it will either sit on the soil, or if it is sloped, the water will runoff.
3. Hardscaping drainage solutions
Given that concrete is installed at a gradient, look around the edging of concrete to see where the water runs off of the concrete.
If there is no drainage material between the concrete and a lawn, grass, or flowerbed, excess water will roll right back onto the concrete keeping it moist for longer than need be.
Simpler drainage fixes are installing a French drain, which is ideal when the soil type is rich in clay making it difficult to dig.
The alternative and much easier fix is a dry creek bed.
4. Dry creek beds stop water pooling on the concrete
A dry creek bed is just a few inches of gravel. Plants can be placed in it too.
These are popular choices for poorly draining soils that tend to experience water pooling heavily causing soggy and muddy soil after a heavy downpour.
The purpose they serve is to slow down the velocity that rainwater moves at.
Putting in gravel or rocks between concrete and a soil bed or lawn holds excess water. By slowing down the speed water moves at during rainy spells, drains around your property cope better.
These do not need to be all rocks or gravel either. Plenty of plants are suited to rock gardens. A dry creek bed is essentially the same, only planted as a narrow stream around 5-inches wide.
To add color with easy-to-maintain flowers, learn about how to grow creeping avens. Alongside concrete paths and creeping up through different sizes of rocks is how these plants grow.
Rather than a barrage of water filling the drainage system up so fast that it overfills and backs up onto the concrete, the excess water soaks into the gravel then drains away slower. Even slower when plants are there to drink it.
It beats all that rainwater flowing right back onto concrete, bumping its moisture content up to the extent that moss finds it to be the ideal habitat to start germinating on.
Frequently Asked Questions about keeping moss from growing on concrete
Does ferrous sulphate stop moss from growing back on concrete?
Ferrous sulphate is an iron solution that kills active growing moss. Moss has rhizoids as anchors instead of roots and moss reproduce asexually through its spores. Chemical moss killers only kill active growth. It will return. The only way to stop moss growing on concrete is to reduce moisture.
Are moss removal services worth it?
Moss removal services get rid of moss. They do not treat the cause. Driveway contractors can rectify improper sloping. Tree surgeons help by cutting back overhanging branches to open the concrete up to sunlight. Roofers know more about channeling rainwater from downpipes to suitable spots for drainage.
Marcel runs the place around here. He has a deep passion for houseplants & gardening and is constantly on the lookout for yet another special plant to add to his arsenal of houseplants, succulents & cacti.
Marcel is also the founder of Iseli International Commerce, a sole proprietorship company that publishes a variety of websites and online magazines.