What could be simpler, we’ve all done this as early as kindergarten, right ? Poke a seed in a Dixie Cup of soil, re-hydrated Jiffy Pot, or just a folded-up damp paper towel and presto, nature’s magical transformation of a dormant seed into a living plant begins before our eyes.
A few days later your hopes are dashed as the once robust green seedling droops over. Maybe you drive the final nail into the coffin and water it some more at this point, sound familiar? Close observation might reveal that the base of the stem is discolored and shriveled, which led to the droop.
Damping-off of seedlings can be caused by several pathogens, but most commonly the culprit is Pythium. ( http://www.ipm.ucdavis.edu/PMG/r783103111.html ) By loving our babies too dearly with excessive water, nitrogen, and warm humid air we sometimes create the perfect conditions for Damping-off. If you have Fungus Gnats starting to crawl and fly about, they are probably carrying and spreading pathogens which could lead to Damping-off.
There is nothing you can do to save a seedling once it topples over, but if you have other sprouts in the same medium you might be able to stop the disease from spreading to them. Remove the diseased plant, be sure you get all the infected roots. I’ve had some success with two home remedies to arrest the spread of Damping-off. With an eyedropper, apply about a milliliter of Hydrogen Peroxide to the soil surface at the site of the problem; the 3% solution drug stores sell for antiseptic purposes works fine. You might see some white foamy bubbling action for a second or two. Alternately, or in addition, you can sprinkle about an eighth of a teaspoon of freshly ground cinnamon powder on the soil surface.
You can avert future Damping-off disasters with a few common sense precautions. Don’t start your seedlings in “dirt”, use sterile fast draining medium such as rock wool or perlite. Measure and control the pH of the water, don’t use even dilute fertilizers or teas on your seeds and seedlings; they get all the initial nutrition they need to start life from the seed leaves or Cotyledons. Control the humidity of the seed starting environment, resist the temptation to create a warm foggy incubator with a covering.
Disclaimer: Any advice and opinions offered about the cultivation of cannabis by Bruce N. Goren are his own and do not represent the University of California or the Master Gardener Program.