With the first gleam of morning rays, the garden is a prism of a thousand hues refracted in tiny does of crystal dew, a dazzling quilt of millefleur colors covering the sleeping flower beds. ~Duane Michals
You've followed all the sowing instructions, waited patiently for your seeds to germinate, and then they fall over and die very quickly with no warning. This is often what people call "damping off", which means one of several fungi have infected the seeds or the seedlings and cause them to rot and die. The key to avoiding damping off is preventing the conditions that the fungi like and giving your seedlings the best chance at growth.
Follow the instructions on your seed packets exactly as to the depth you should plant the seeds. Sowing too deeply can cause problems, as can crowding the seeds together. It's important to give them enough room to grow. If you need to thin the seedlings after they germinate use a sharp pair of scissors to cut them off at the soil line instead of pulling them out.
You should follow the instructions on temperature for germination and group seeds together that need the same temperature. Some gardeners swear by placing a light coating of sand or vermiculite on top of the seed starting mix after sowing. Another thing to use is a finely ground sphagnum moss. The University of Minnesota recommends this:
"Sphagnum moss is sold in small bags in garden centers, and is not the same as the soil enhancer sold in bales. You will need to make a fine dust, so toss a handful of the moss into a blender, put the cover on, and hit puree. When the dust settles, tap it into a container for storage. After planting your seed trays, sprinkle the sphagnum over the soil surface, just enough to cover."
Even moisture, but NOT soggy conditions is also important. You don't want them to completely dry out, but you don't want to soak them either. I tend to gently drizzle water into the soil. Once the seeds germinate ALWAYS remove any top covering you
had on the container.
Another thing that is important for your seedlings is good air circulation. An oscillating fan placed near the seedlings JUST enough so they sway very slightly will be all you need. Do this for a couple of hours per day. A ceiling fan on low in the room will also work. Lastly, you can make a chamomile tea solution with 2 cups of boiling water to 1/4 cup of dried chamomile blossoms or use 4 teabags of straight chamomile tea. Cool the tea and place it in a spray bottle. This spray will be good for a week. Mist the soil and the seedlings lightly and the properties in the chamomile will help keep fungus at bay. I did this last year and it worked really well with my seedlings.
More on preventing damping off on OFL:
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