Best way to avoid seedlings from bending and dying

Question

I love starting plants from seeds. I love the fact that from something tiny comes out something so amazing. I find, though, that I have a very bad survival rate with my seedlings. I would say 90% of them bend and die, which I have read it is because of a fungal disease at the soil level. I was wondering if I could have some tips to avoid this problem.

This is what I do.

• I plant my seedlings in small newspaper pots like these: http://bonzaiaphrodite.com/wp-content/uploads/2009/03/img_9738.jpg
• I use seed starting mix, not soil.
• I water them from the bottom letting the paper and soil to absorb the water.
• I place the pots in a plastic box and cover them until they germinate to maintain moisture.
• When a pot germinates, I move it to a different uncovered box to increase air circulation.
• The problem happens even in pots that are not overcrowded (2 sunflower seedlings, for example) and with all sort of sizes of seedling (from petunia to sunflower).

Answer 1

I know several things that should help for damping off. Most of these are based on personal experience rather than things I've looked up.

1. Don't use containers that decompose. They attract mold. Pythium, which can cause damping off, is fungi.
2. Put a 22+ watt 2500k CFL lightbulb (on) near your plants. In my experience, this kind of light seems to protect against damping off more than the highly recommended 6500k lights. Maybe pythium doesn't like infrared light (which should be somewhat higher in 2500k bulbs).
3. Make sure the soil level isn't too far below the rim of the container. Your soil is quite far below. This provides a more ideal environment for damping off. Sometimes, after watering the first few times, the soil will lower. You can reduce this by initially compacting the soil more. If you're using seed starting potting soil, this shouldn't be too much compaction for your seeds. Compacted soil is generally regarded as bad, but in my experience, it's better than damping off. Other kinds of soil may differ considerably. You could water the soil more lightly to avoid it lowering as quickly, too, somewhat, perhaps. Soil that is too compacted seems to kill seedlings, too, however, but this seems to be an indoor topsoil problem, primarily, and more sunlight probably increases survival rates. The sunlight increasing survival rates is just a guess, based on something I tried once.
4. They say you should increase air circulation.
5. Sunlight helps. More is much better.
6. Put a little extra calcium in your soil, if it can handle it. Basalt rockdust or garden gypsum should work. Don't add too much, though.
7. Don't over-water. You might consider watering with a dropper.
8. Adding some neem oil to your soil might help (depending on the cause of the problem), but I don't know if it would kill beneficial things, too. I've found that completely sterilized (baked) topsoil tends to get moldy after a while, and cucurbits that use it have smaller leaves. Plus germination rates (at least for plants in the solanaceae family) seem to decrease a lot.
9. You could try adding beneficial microorganisms to your soil to out-compete the pythium. I haven't tried this.
10. Use fresh soil (not something that has been lying around for a really long time or has been used by other plants).

Damping off probably isn't the only thing that causes the symptoms you describe. Are the seedlings just falling over or do they look rotted/withered at the bottom of the stem? If they look withered there, it's probably damping off. If they don't, they might need more rest from whatever light you're giving them or something. I find that some of my tomatillo and pepper seedlings sometimes fall over if they get too much fluorescent light, but they recover some if I give them more rest. At least, that's how it seems. I could be interpreting what happened incorrectly due to the scarcity of occurrences.