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Dealing with damping off

Sterilizing a seedling flatLast spring, I had trouble for the first time with damping off.  This fungal disease is evident when seemingly healthy seedlings die near where their stems meet the ground.  When you're itching for the first seedlings of the year to push forth their greenery, damping off can be very traumatic for the gardener.  (Okay, maybe that's just me.)

Since I was using the same stump dirt as in previous years, I felt that the issue last year might have been problematic fungi colonizing my old seed-starting flats.  Sure, I could have bought new flats, but I thought it would be easier (and definitely cheaper) to simply soak the ones I have in bleach water for about half an hour.  After that, I filled up the flats and seeded my onions, then made a control flat out of a rotisserie-chicken container.  (Rotisserie chickens seldom come home with us, but we had a long day in the big city last week and I was too exhausted to cook, so Mark bought one as a rare treat.)

Damping off experiment

Hopefully I won't see any damping off at all, but if I see it in the store-bought flats but not in the chicken flat, I'll know I was right about the flats being the problem (and wrong about the bleach water curing it).  On the other hand, if I see damping off in all the flats, I'll know the stump dirt is the problem and will have to consider one of the mainstream cures --- either buying real potting soil or sterilizing my stump dirt in the oven.  I like to think the bacteria and fungi in my unsterilized potting soil are good for baby seedlings, but I could be wrong.

Other possible ways to deal with damping off include tweaking the environment and using home-made sprays.  The fungi involved like cool, damp conditions, so if you can warm things up (maybe with a heating pad under the flats) and keep watering to a minimum, you might be able to whip the bad microorganisms even if they're present.  Some gardeners even make chamomile or garlic tea and pour it over their potting soil to protect the seedlings.  I'll let you know if I have to resort to any of those extremes, and if so, which ones work.  In the meantime, feel free to chime in about your battles with damping off in the comments.



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Your great-grandmother, Anna, before the days of plastic, used homemade wooden flats, that she washed with dish detergent, I think, and sterilized the sifted potting soil in the oven. She covered them with newspaper, watering thru the paper till the plants emerged. I wish I remember what she ever did about damping off! Somehow I have a feeling that some of that might be because of the air-tight planting flats you have...I personally don't like to sterilize in the oven because it dries out the dirt so much! But I like the idea of garlic or chamomile tea, poured thru newspaper.
Comment by adrianne Wed Feb 5 08:13:40 2014
I'm betting over-watering encourages fungal growth more than mere contamination as a factor. Fungal spores, after all, are every where all the time. (Leave a piece of bread out on the counter for two days to prove it.) I just use garden dirt or partially composted manure as my growing medium and don't have any problems unless the top of the soil remains wet.
Comment by doc Wed Feb 5 09:56:47 2014

Hi All,

One of my local farmer friends sterilize his compost in a steel bucket on the top of his wood stove. He adds a gallon of water. He pokes a compost thermometer into the bucket and waits until it reads 150F throughout.

He is one of the most successful farmers I know. Doesn't get in line for gov. handouts, runs multiple hoop houses bought with his own dollars.

Kinda like you (Anna and Mark)! Pretty exceptional guy.

So I would try heating some of your starter soil to "kill bad stuff" to see if that 'cures' the problem.

I seem to recall that you don't want to get it too hot? I can't remember why?

warm regards, John

Comment by John Wed Feb 5 10:13:40 2014
Allow me to quote Eliot Coleman: "In more than 20 years of using homemade mixes, I have never sterilized them. And I have not had problems. I realized early on that damping off and similar seedling problems, which are usually blamed on unsterilized soil, are actually a function of cultural mistakes like overwatering, a lack of air movement, not enough sun, overfertilization, and so forth. Good, fertile garden soil and well-prepared compost contain many organisms that benefit seedling growth. If you "sterilize" these ingredients you lose the benefits of a live mix without gaining the advantages that are achieved through proper seedling management. Recent university studies agree and emphasize the specific value of finished compost as a disease-suppressing ingredient in growing mixes." Your stump dirt may be a good compost substitute, as is worm castings, but you need some real soil in there to moderate any excess nutrients in the compost/substitute, as he explains elsewhere. [The New Organic Grower, rev. ed. pp 138-141]
Comment by jackie Wed Feb 5 16:28:41 2014
Actually, having just reviewed your post on the characteristics of stump dirt, I suspect you could make a superb potting soil using Eliot's recipe [p 140] but substituting stump dirt for peat moss and worm castings for compost.
Comment by jackie Wed Feb 5 16:40:36 2014
seems like I heard that putting ½ inch peat moss on top of your soil mix will prevent damping off. might be worth a try if you have a problem again this year.
Comment by Katherine Thu Feb 6 18:44:14 2014
I had problems with dampening off every year except last year when I began running a fan 24/7 in the room with my seedlings. I hooked it up near the ceiling and not pointed directly at the plants. I also sprinkled cinnamon, a natural fungicide, on the plant surface. I did sterilize the soil but this was to kill any gnat eggs, which also had been a problem.
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