Algae on media

Anytime I start seeds indoors under grow lights, I get huge algae problems on the media. And this seems to happen even if I let it dry out to the point of wilting before watering again.

It never seems to hurt the plants, but it’s ugly, and sometimes requires me to break the crust so I can water.

I sprinkle perlite on the top of the seed starting mix after planting and usually water from the bottom of the tray. Also, if reusing planting trays or packs, I wash them with detergent or a weak bleach wash. No algae.


Perlite is a good idea (except for super-tiny seeds, perhaps).

I see all the time the recommendation to sprinkle cinnamon on top. maybe boil or soak the powder first and add it to a spray bottle.

1 Like

I used it with seeds so small I needed my reading glasses to plant them.:seedling:


That is the size of most seeds now!!:smile:

Yeah same issue here. I suspect its to do with lack of UV, low air temps or lack of radiant heat because it doesn’t happen outdoors. But yeah perlite, rice hulls or any fine mulch will hide the algae. Fortunately it doesn’t harm the plants at all.

Sometimes i wait until the seeds have sprouted before adding the perlite/ rice hulls.

Water from the bottom and not enough so that the top gets wet, after all we dont want roots at the top of the soil so no need for water up there. I never here much on here about h2o2 but its use in the garden is priceless. 1/2 cup per gal and put in sprayer. Spray the top of the soil. Also works well for the times when you overwater and get root issues.

My problem with bottom watering was that the roots would grow through the pot bottom and into the tray, and when you go to remove the root ball from the pot they get torn off leading to more transplant shock.

1 Like

No matter how you feed them if they are healthy they are going to grow out of any pot. I do not understand the transplant shock thing with peppers or tomatoes, I am down right abusive with my seedlings when potting up and have never seen any transplant shock. When I was selling seedlings I would grow hundreds in a 4x4 inch pot and when they were in need of transplanting I would just pull them apart and up pot them.