How to control algae on soil surface

[cthulhu]

my friend has a few plants which he is growing in Pro-Mix mixed with cow and sheep manure. he waters the plants once every 2 days, but was watering them once a day until I told him that he was probably overwatering. his plants show symptoms of overwatering, wilting/yellowing leaves and generally slow growth but since he has been watering every 2 days they seem to be improving.

he has had some green mossy like substance growing on the surface of the soil for the last few weeks. at first, I overlooked it thinking it was likely some sort of peat moss, considering Pro-Mix is like 90% peat moss. since he has been watering less often it has actually appeared to have gotten worse, and it is now clear that it is not actually moss, rather a thick green slime.

the question is, how do we control it without applying some nasty chemmy fungicide? I know it needs light and moisture to grow, so what do you think would happen if we just topped the pots up with fresh soil (covering the algae, blocking light)? Would it eventually die off or would it just consume the new soil?

 

[10k]

Just let the soil dry out more between waterings. Go ahead and scrape away the top inch or so of soil when it's dry, then top dress it with some fresh soil. You shouldn't be growing algae if you're watering properly at less frequent intervals. The soil does not have to be continuously wet on top. Please click my "lift the pot" link. Keep in mind that just because the soil is dry on top means nothing as far as how wet the soil may be deep in the planter where most of the root system does it's magic.

 

[limey]

Just let the soil dry out more between waterings. Go ahead and scrape away the top inch or so of soil when it's dry, then top dress it with some fresh soil. You shouldn't be growing algae if you're watering properly at less frequent intervals. The soil does not have to be continuously wet on top. Please click my "lift the pot" link. Keep in mind that just because the soil is dry on top means nothing as far as how wet the soil may be deep in the planter where most of the root system does it's magic.

Agreed though I think one should be very careful scraping away from the surface as the critical nutrient uptake roots tend to be close to the surface of the soil.

Also worth considering covering the soil around the stem with lightproof plastic (though do make sure there is some airflow underneath) as algae and moss both need to photosynthesise and will die away with no light... being careful of course not to over-water as you can get fungi growing around the stem, which is even worse!

 

[Philosophelon]

Also, a 1" layer of chunky perlite on top will dry out very quickly, and block most of the light from reaching the soil surface without blocking airflow. I do that myself to avoid fungus gnats/white mold/etc., because perlite drys so much faster than soil (or coco, in my case). It might help with your algae problem, and it's a pretty cheap option to try.

If I have a contamination issue already (like green slim growing on my soil) I use Hygrozyme. I use it regularly in a lower strength as a preventative as well. It's expensive, but it's organic (it's made out of some sort of super-secret proprietary enzymes), and does a hell of a job on most of kinds fungus or bacteria.