how to reduce algae growth on surface?

[maxjohnson]

What do you to to prevent green algae from growing too much on the surface of potting mix? What do you spray on the surface and not harm the seedling and germination rate?

[worth1]

10 percent solution of home use hydrogen peroxide and water in a spray bottle might help and it won't hurt the plants.
It will also stop damping off.

[Cole_Robbie]

I usually cover seeds in vermiculite to sprout them, and then having the top layer of media be loose and dry helps against algae. Perlite or sand would be similar. And bottom watering also helps.

[bower]

I always take algae as a sign it's too acid - sprinkle of lime works.

[AZGardener]

I moisten my seed starting mix with boiling water. I then water seedlings with bottled water until they are planted in the garden. It has solved gnat and algae issues. I've also moistened the seed starting mix, then bake it until the internal temp of the soil in the pan reaches 165F or 73.8C HTH

[zeuspaul]

I don't recall having an issue with algae. I use well drained sifted recycled potting mix with added sifted perlite and worm castings---no sterilization--no domes. I pre germinate and then place under grow lights. I top water. If it's sunny (almost every day) and not too cold I carry the trays outdoors and place in the sunshine, then back inside at the end of daylight.

[karstopography]

I haven’t had issues with algae either. Absolutely no domes for me. Jiffy soilless seed starting mix as a top layer, Baccto premium potting soil below. Top layer will show signs of drying out a bit (color change) and trays will lighten up a bit before I add additional moisture.

Trays go outside on warmer days, top water only if necessary, mainly heavy misting or gentle sprinkling outdoors.

I don’t keep my trays in a dank basement either. They are either outside weather permitting or in the garage, but either way, there’s plenty of air circulation and sunlight on them if possible.

[GoDawgs]

Like @karstopography I grow all of my seedlings just a tad on the dry side. Not really dry but if the containers start feeling a little light I water from the top sparingly. No gnat or green problems. They are grown indoors under lights and then hardened off out on the front porch when it's time.

[JayneR13]

I have had this problem. I grow my pre-sprouted seeds in a potting mix covered with plastic until the seedlings appear. Then I give a small shot of water several times per day until the root system gets established, decreasing how often along the way. I have my seedling rack in a spare bedroom and open the window if I can. I also use a heat mat since March-April can still be quite cold here. I find that breaking up the soil with my fingers and allowing it to breathe definitely helps get rid of any mold. I may give the peroxide a try.

I tried baking my mushroom mix back when I was growing them. No dice. Five hours in the oven and I never got a single shroom from the monotub! And the house stank, not to mention what that does to my energy bill. No thanks in my nursery.

[AKgardener]

I have well water I also get a little bit but not enough to cause it to be covered I usually keep my ceiling fan on all day .. I do sterilize my mix with boiling water and for the most part I never get gnats every now and then I still get a few regardless but never a bad infestation..

[pepperhead212]

I make my own seed starter mix every year - relatively simple, with just about 65% peat and coir mixed, then 10% worm castings (add this after the heating), and 20% perlite and 5% granular DE. I sterilize it by heating it in a foil tray in my grill heated to 175°, or thereabouts, and then I let it cool off. When cooled off, I mix in the worm castings, then some of that granular micorrhyzae, and mix well, then I moisten it with some filtered water with a little of the hydroponics nutrients I use (MaxiGro, for greens, and some silicate nutrient, which I've found helps get stronger stems), and a small amount of the liquid Bt israelensis (Microbe Lift), to prevent any possibility of fungus gnats. I only use that once, but add the small amount of hydro nutrients every time I water (a tsp of Maxigro, and 1/4 tsp of the silicate solution to a gallon), but I let them dry out somewhat each time. The hydro nutrients and worm castings are the only fertilizer I add. I never have algae problems, in the time the seedlings take to grow to size.

[Homegrwoninillinois]

I bottom water only and run a fan letting the top portion of soil dry out pretty well before watering from the bottom again.

[bower]

Oh boy.. I'm really getting the algae bad this time.
The couple of bags of promix I picked up in the fall had been out in the yard, and I realized when I picked them up they had gotten wet. No actual algae in the bag but certainly lots of spores. Probably overwatering too, trying not to let the tiny strawberry seedlings dry out. No control of temperature or RH in the basement and under the lights, whatever combo of conditions the algae really likes it haha. I've been potting some things up and now I'm getting it on the freshly potted plants as well, drat.

So I'm looking for ways to get rid of it. I might or might not have some lime that I can crush to a powder and not put the seedlings into pH shock. For larger pots i'm not worried but the cell packs might be an issue.
Just saw this video, which gave two more suggestions for algae control: 1) vermiculite on top and 2) cinnamon sprinkled on. They also use cinnamon tea... I'm curious about that.
Anyway, thought I would share this video.

[ddsack]

Let us know if any of the video methods end up working well for you. I normally don't get a lot of it, except on seedling peppers that are slow growing and don't get transplanted when they should. I normally just scrape off the thin green layer on top and discard it, and perhaps top off with fresh mix if the seedling requires it. I wonder how far down the actual algae filaments bother the plant roots as far as competing for nutrients. It seems like the algae is more of a surface slime thing that has more effect in sealing off the top of the cell from a good oxygen exchange, rather than taking away nutrients deeper in the soil. I do consider it a visual blight, but am not sure it actually harms the seedlings, other than being an indicator of too much wetness ???

[leftylogan]

When I worked a season as a commercial (wholesale) grower one of our busy work tasks was to scrape the algae off. It was not a priority task whatsoever and didn't get scraped off before shipping either. I don't bother too much with it for my personal plants.

We had fertilizer direct injected to the water supply for each greenhouse and everything was watered at least once daily no matter what so the algae grew quickly but never very deep.

[bower]

I did try the sprinkle of cinnamon, since I had some around. It didn't bother the plants and it might've helped by "smothering" the algae. I agree with you @ddsack that the worst effect is on oxygen exchange, making a sort of hardened cap on the surface. So scraping or picking it off is as a good thing to do as any. I used a toothpick to break up the cinnamon covered surface after a few days as well. Hard to say whether the cinnamon made a positive difference, but I'll see whether algae regrows in the mixed surface soil.