Help with Damping off issues

The last two years, I have had serious damping off/fungal issues. (Just lost the entire first flush of seedlings! Last year, I thought I might have overwatered in hopes of holding my seedling over during a holiday visit, but this year I thought I was more careful.)

Obviously I seem to have some hygiene issues, but without resorting to carcinogenic chemicals, I wonder if anybody has insights as to add’l practices that might help. (To avoid thrips and other problems elsewhere in my house and garden, the seedlings end up in my bedroom windows, so toxins are out of the question.) I think I read that bottom heat might push seedlings through the sensitive phase of life more quickly, for instance. Can anyone confirm? Also, I was using more sustainable and environmentally-friendly coconut coir instead of my old peat-based standby, but wonder now if in fact the peat’s antibiotic properties might help than I wanted to believe.

Any mixes that folks swear by, or tricks to maintaining the ideal moisture in the medium?

Thanks in advance.

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Hi Phillip!

I haven’t had any damping off since I went to 50:50 sphagnum based seed starting mix to ultra fine perlite. I sift medium perlite with a kitchen sieve to get the ultra fine perlite.



I’ve had good luck for many years with a blend of peat moss and a commercial compost and manure mixture (probably about 60:40 most of the time, but the exact percentage doesn’t seem to be important and I don’t measure). For me, peat moss by itself is sort of a wild card, with some batches behaving better than others when mixed with sterile ingredients. I don’t doubt that its acidity is helpful in preventing certain problems, but damping off doesn’t seem to be one of them. Evidently the presence of antagonistic microbes is key, and that can vary from batch to batch. The addition of commercial compost/manure seems to help provide any missing microbes, and it also seems to create a good soil environment for the developing seedlings.

Another thing that helps to avoid the spread of damping off from pot to pot, should it appear, is the prevention/minimization of fungus gnats. Mosquito control bits work very well for this as a non-chemical control (they’re also labeled for fungus gnats, at least in the U.S.). You can either add them to the water that you use for the seedlings, or sprinkle them on the soil surface. Since seedlings and seed pots tend to be so small even compared with the bits, and since the bits might not all release their bacteria unless they are directly hit by water, I prefer to add them to the water first. That presumably spreads the bacteria around more evenly and quickly.



This is a relatively new problem for me. I used to have minimal loss to damping off. Tony, do you sterilize your peat mix, or use it as is, putting your faith in the enzymes?

One of the supposed benefits of coir is that is allegedly less attractive to fungus gnats.

Stefan, I concur with the concept of beneficial microbes, and have wondered how that bears out in reality. I fear that compost might contain famished microbes in excess that could then attack a seedling with an “infectious dose” of an ordinarily benign microbe. How do you control such? Someone (it might have been you) claimed letting fish emulsion age into a medium provide antagonistic microbes, but I now feel compelled to sterilized media to a greater extent.

Do others use warming pads beneath seedling trays?

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For a long time I have been using a purchased peat mixture, which I sterilize and then add perlite, sand, worm castings and vermiculite. I also use heat mats for the first two weeks, during the day, not at night. As the heat from the mats naturally dries out the soil more quickly, you should water twice a day with 3-4 drops of water per seedling and check the humidity in the environment. 70 - 75 % humidity is ideal. More leads to mould. I use a syringe with a cannula for watering. You can use the cannula for very fine dosing and when the seedlings are some days older, you can simply prick deeper into the soil so that the now longer roots also get moisture without overwatering. With this method, I had very less failures in the first period after germination and even manage to help seedlings that have little difficulties for getting a better start-up to live.


Actually, composted products including manure are full of beneficial microorganisms and relatively free of harmful ones. Using such materials improves the health of rose seedlings, and I rarely experience damping off. When I used peat and sterile products like Perlite and vermiculite, my results varied widely. I resorted to all kinds of tricks to try to minimize damping off (fans blowing, layering Perlite or sand on top, etc.), but my success rates barely budged. If you sterilize the media, when a harmful organism does appear (such as on the aril/seed coat), you’ve ensured that there are few beneficial organisms left to help prevent them from killing the seedlings outright. Healthy “soil,” not some futile attempt at sterile culture, is the key to minimizing damping off in my opinion.

Yes, I’ve previously mentioned a Canadian study that found it possible to usefully increase the proportion of beneficial microorganisms that were antagonistic to damping off in peat moss by moistening it with dilute fish emulsion and giving it some time before use. It apparently helps to feed the beneficial microorganisms that are already present, increasing their numbers. Of course, that would not work so well if the peat has been sterilized first, and isn’t the most convenient method if you don’t plan ahead!



I stopped using peat and coconut for seedlings. Instead, I opt for mixing mostly basic potting mix (without peat) w/ a minor amount of very aged steer compost for the low amount of hard minerals. I buy the compost at the end of winter, where it is quite aged.

If I am doing this indoors, I would opt for wholly sterile soilless media, like perlite and a low ratio of chunky vermiculate.

This is from years of trialing different ways of germinating in a climate where downy and damp off are commonplace.

Coconut coir, and sometimes peat, can also lead to root gall in August as the seedling roots mature. It can get really nasty lookin’.

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I have eliminated my damping off issues by keeping their temperature always above 70 degrees and adding a diluted watering that includes CEASE fungicide to the seeds, once at planting, and to the germinated seedlings one time after sprouting.

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I like the idea of CEASE. That sounds akin to what I was wanting when talking about healthy microbes and inoculations. as I say, I grow starts inside, and I have a child, so I refuse to use anything toxic.

But I only see it by the gallon, and at a rather dear price. I assume that as a product containing living organisms in it, it has a short shelf-life?

Anybody familiar with Bacillus amyloliquefaciens strain D747 as it is found in e.g. Southern Ag Garden Friendly Bio Fungicide Organic? This one is scary cheap in comparison to CEASE ( Bacillus subtilis strain QST 713)

I need to dig for some scholarly articles on the two, I suppose…

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Why was No Damp banned?