Damping off is where your little bitty seedling goes limp and dies. One after another, they spring upward from the dirt and form their cotyledons (Their first baby leaf. Science!) but die before forming their first true leaves. It's distressing to see entire trays wither this way, one after another, boink, boink boink, the whole tray dead.
What causes damping off?
My first guess is overwatering. Because it looks like they're soaked.
My second guess is under-watering. Because watermelons and carrots really like water.
*looks* [why do seedlings dampening off?]
Both guesses are wrong.
* It is caused by a fungus or mold that thrives in cool, wet conditions.
* To prevent dampening off, use sterilized pots or trays with good drainage and use clean, new potting soil.
* Once plants have mature leaves and a well developed root system, they are better able to naturally resist the fungus or mold that causes damping off.
* There is a critical period of growth between planting and maturity when special care needs to be taken to protect sensitive seedlings.
* The most common pathogens responsible for damping off are fungi Rhizoctonia spp. and Fusarium spp., along with mold Pythium spp.
* I have no idea what spp. means.
* These pathogens survive well in soil and plant debris.
* The pathogens move easily from plant to plant by growing through the potting media or in shared irrigation water.
To prevent damping off:
* Sterilize all used pots and trays in a solution of 10% bleach and soaking for 30 minutes
* Use new potting mix to fill trays.
* Clean all tools.
* Use heating pad.
* Use pots with good draining holes.
* Use warm water to water young seedlings.
* Do not apply fertilizer.
* Provide 12-16 hours of light. A window is not enough.
* Know the best temperature for each species of seed.
Information by Michelle Grabowski, Extension.umn.edu.
She didn't suggest spraying the seeds and medium with hydrogen peroxide like the Baltimore microgreens guy does. Shown to us by John Kohler.
So, now I know. It's not the fault of the three packages of watermelon seeds, nor of over watering, rather, it's the fault of using Jiffy pellets and setting them in trays of water.
Lesson learned.
Next year seedlings will be in little pots that are watered from the top and drain on a rack in a tray so the water is not shared between them. That way I can control the growing medium and not rely on peat.
Know what's a bummer?
My little plants that lived are infants while the plants offered outside at the grocery store are 5x further along. They started a lot earlier than I did and their little pots are a lot better than the Jiffy pellets that I used.
It's like they have this all figured out scientifically already. A lot better than I do. They win.
Bastards.
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