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Weeds, Moss and Algae on Paving

By: Chris Hogan MSc - Updated: 25 Apr 2013 | comments*Discuss
Weeds Drive Moss Algae Clean Path

Algae, moss and eventually weeds can take over a newly laid drive unless you keep an eye on the situation. Regular applications of weedkiller and path clearing products will keep them under control, but many people don't like using these chemical products because of the damage they can do to the food chain.

The Links Between Algae, Moss and Weeds

Less invasive weed control products can help but regular cleaning is the best way to keep weeds and the like from growing on the drive in the first place. They are all linked together because each provides a foothold for the other. Algae break down the surface of a path, moss will then get a hold on the algae, and the seeds of small plants can grow in among the moss and its roots.

It doesn't necessarily happen this way though. Weeds can start growing on their own, particularly on block paving with sand infill, purely by seeds getting lodged in the gaps and sending roots down into them. Much is made of weed barriers being laid down beneath the surface of paths and drives, but the truth is that very few weeds will break through from the underside if proper substrate layers have been put down. Nearly all weeds arise from windblown seeds landing in cracks and crevices.

Keep Sweeping Away

Regular sweeping is the best way to stop these weeds getting a hold in the first place, but if you begin to get algal bloom over the drive, then a jet washer can be used. Take care with these through, as they are very powerful. So powerful, in fact, that many manufacturers of concrete paving products are barring jet wash use in their guarantee documents.

Hold the jet wash wand at a shallow angle and try not to direct the jet into the crevices, particularly if they are filled with loose sand as it will be washed away. Try the jet washer on an inconspicuous corner of the drive if you are concerned that it might start to break up the top surface of your paving or blocks.

Removing Moss and Weeds

If moss and weeds have got a hold already, or you move into a property where basic maintenance and cleaning has been neglected, what's the best way to get rid of them?

The jet washer can be used on moss but it may pull out more than the roots, meaning you'll have to reinstate sand in the gaps. Mechanical scraping and levering with a hoe, being careful not to scratch the block faces, is the most permanent way of removing moss and most weeds.

Some moss-killers will destroy the moss but you still have to get rid of the dead stuff left behind, which means you're back to scraping again. So you might as well not bother with the moss-killer bit, particularly as some of them will stain the blocks orange as a result of the iron sulphate content.

Choose your Weapon

If you do resort to weedkiller, avoid general products which will indiscriminately kill anything on contact. It's better to use a product that has been developed for paths as it is likely to be less indiscriminate.

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To be honest, I've always found scraping and then washing with a natural detergent that won't damage the water table to be the most effective solutions. You can concentrate on the areas that need it most and it works better than a pressure washer (and uses less water). It takes time and effort, but when you've finished the path looks great, almost as good as if it had just been put down. Do it once a year, at the end of spring and you won't regret it.
nick - 4-Jul-12 @ 9:32 AM
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