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The soil looks like it has only very small particles which bind so closely together that there's no air in the soil. It looks like mud. The size of the pots is large compared to the seedlings. Probably 2 days is not enough drying time before adding more water. I do see what looks like spider mite damage (the white spotted leaves) and some seedlings damping off. Fertilizer may have been used too soon. Hopefully someone with more experience and knowledge of your zone can give you some more specific advice. Growing from seed exasperates people even after decades of trial & error, so don't give up or be too hard on yourself!

Your plants look like they are not getting enough light...are you placing them in sun 'after' they germinate? I would re-seed them in their permanent homes(be it in the ground or in larger pots)out in the sun to start, keeping the soil just moist, not wet. I would also refrain from fertilizing until they get a few sets of true leaves. If you are going to grow them in pots, you would be better off purchasing 'potting mix' as opposed to using 'backyard soil' in pots.
Also, Zinnias don't like being transplanted and do better started where they are going to grow. I have started them in cups before only to have them do poorly when transplanted. I've then re-seeded right next to them and watched the new seedlings thrive and surpass the transplanted ones. I have transplanted Marigold volunteer seedlings many times and they pout for a while, but finally take off and do well, so maybe they also would do better seeded directly in the ground. HTH
The link below might be of some help if you have not already been there.

Here is a link that might be useful: Growing from seed FAQs

Ditto from above.

Looks like growing in mud,
with not enough light after germination,
and high fertilizer levels:

just the right combination to cause damping off.

Direct sunlight from the start is best.
Many times people don't do this is because they start indoors or in heated greenhouses to get an earlier start (i.e. it is too cold outside for direct seeding in the ground or in pots). So they need to "wean" them back to full sunlight gradually.

If it is already warm enough, plant in direct sunlight.

Your best garden soil in the world will never work in pots. The sowing mediums formulated for growing in pots and containers are soilless for a reason, emphasis is on areation and drainage for good root development. Your seedlings are not getting that.

And I agree they look like they are starved for light. As for the fertilizer, when needed, a dilute formula is best - for seedlings 1/4 strength the product directions generally plenty for seedlings, you don't want to force upward growth, what you want at this stage is healthy expanding roots - and plenty of them. Those roots will lead to nicely sized garden plants later.

Hi. Thank you for all your inputs.

I followed your advice and made do of a sterile soiless starter mix.
The results however are confusing.

In the first pic, the stem seems pinched on ground level; the second pic shows the top most portion of the stem (leaves as well) 'pinched off'

http://i1148.photobucket.com/albums/o568/sammyyummy1/10062012190.jpg

http://i1148.photobucket.com/albums/o568/sammyyummy1/10062012187.jpg

What happened and what am I doing wrong?

The seedlings had sufficient sunshine (direct) in a well aerated areas. Watered as needed.

[img]http://i1148.photobucket.com/albums/o568/sammyyummy1/10062012190.jpg[/img]

[img]http://i1148.photobucket.com/albums/o568/sammyyummy1/10062012187.jpg[/img]

If the plant stem looks pinched at the bottom, it could be damping off. Make sure you aren't overwatering and have proper air circulation. Seed starting mediums that contain soil are sometimes to blame for damping off too.

"sufficient sunshine (direct)"

It doesn't appear to be direct light. Are you using window light, artificial overhead lighting, actual sun outdoors or just what? Also, at what approx temperature do you have your pots if you are in control of the heat. The temperature after germination if starting indoors is often lower than that needed for the seeds to sprout.

Thanks. I'm quite confused with my soilless starter mix results. After germination, the seedlings had direct sunlight, they were placed in a well aerated area that I often had to check if they have dried out. I allow soil to dry out before watering. Watered once a day. Yet the results are as above. I experimented on one using a diluted h2o2 -water mix but again, they pinched out and tipped over. What am I doing wrong still?

For those who asked, the backyard soil I used prior to the soilless mix with sad results (see first post above) is heavy clay. I've noticed that germination and growing seems faster and more robust but again, the seedlings dampened off. I've realized that after watering they seem to compact tightly like a brick. Could my seedlings (first post pics) tipped over, discolored due to this compactness? Since using soilless mix did nothing for me, can I amend the clay with gravel?

Argh my supposed stress buster gardening has made me hapless. Please help!

Please please help.

Hi thank you
I also forgot to mention.

I belong to zone 11, generally nice sunshine throughout the day, temp especially during the summer is around 80s, upper 80s.

Recently, some of my seeds started sprouting and noticed white fuzz around the stem where they emerged. I wonder if this is a cause for alarm (warning sign of damping off etc)

[IMG]http://i1148.photobucket.com/albums/o568/sammyyummy1/12062012194.jpg[/IMG]

[IMG]http://i1148.photobucket.com/albums/o568/sammyyummy1/12062012193.jpg[/IMG][/img]

Hi thank you
I also forgot to mention.

I belong to zone 11, generally nice sunshine throughout the day, temp especially during the summer is around 80s, upper 80s.

Recently, some of my seeds started sprouting and noticed white fuzz around the stem where they emerged. I wonder if this is a cause for alarm (warning sign of damping off etc)

[IMG]http://i1148.photobucket.com/albums/o568/sammyyummy1/12062012194.jpg[/IMG]

[IMG]http://i1148.photobucket.com/albums/o568/sammyyummy1/12062012193.jpg[/IMG]

[img]http://i1148.photobucket.com/albums/o568/sammyyummy1/12062012194.jpg[/img]

[img]http://i1148.photobucket.com/albums/o568/sammyyummy1/12062012193.jpg[/img]