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I have cement base under my lawn therefore my lawn has just 7 inches of soil and then below that it is fully covered with cement. This is done to prevent water seepage in my basement so I can't drill holes in it to improve drainage because then my basement may suffer from water seepage. As there is cement base during heavy rains due to poor drainage I can see green algae at some places in patches. After few days when sun falls on it it turns to black and looks very ugly. I just pour handful of soil over it to cover it up. So, basically I am just hiding the problem instead of solving it.

Is there any solution to algae? May be pouring diluted vinegar but I read it can harm the grass as well. I need some solution that can kill the algae but not my lawn.

Any help is appreciated.

Edit:

So here is the picture I found from the internet. You can see the green colored substance in the picture. If I rub my fingers it feels Jelly like. This is exactly how it looks and once rain stops and sun falls on it it becomes completely black:

enter image description here

TCM
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I assume you are talking about moss not algae... If so it isn't actually dead when it is dry, just dormant... I wouldn't worry about it, if it were me, a lawn should shade it out if it is healthy, infrequent deep watering will help the grass over the moss, because the grass has long roots and the moss in non-vascular.

if you are in the US and want to use a chemical herbicide. There are a bunch registered with names like: moss killer, moss super death spray, etc... normally they contain some sort of iron ion: ferrous ammonium sulfate or ferrous sulfate... they should be pretty safe for the environment once they are applied and watered in.

Grady Player
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I'm aware this is old, but there are a couple of answers.

This "algae" is more likely to be a blue-green algae, properly known as cyanobacteria, which are not algae at all, but actually a type of bacteria which can photosynthesize. The most common one in these sorts of situation is Nostoc, which ranges in colour from dark green, almost black to brownish.

The only long-term solution, is to improve drainage, which may or may not be possible based on your situation. The best manner for this to be done would be using "french drains", which are layers of gravel used to direct water into a conduit so that it drains away from your basement. French drains are a common solution for prevention of water incursion in foundations and basements. Obviously this only works if you can direct the water away from your basement - if every point in your garden slopes towards the house, then this won't work, though you could direct the water to a sump and then pump the water out.

Another solution along these lines is to not have this area as lawn - either convert it into a garden with wet tolerant plants such as sedges and reeds, potentially even a small pond, or pave/cobble-stone it and use it as a hard surface area.

There are chemical treatments, usually marked as "for moss and algae" and they do work temporarily. For these to be most effective, you need to remove as much of the mass as possible - scrape it up and dispose, then treat. I'd assume, never having used one myself, that they are not particularly harmful to the grass. Apparently high levels of phosphorus also encourage Nostoc growth, so controlling phosphate additions might help too.

bob1
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