Would it be problematic to bury the whole stem of the seedlings under the potting mix so only the leaves are above it? Because this seems to be the only solution coming to my mind for the seedlings who are falling on side due to thin stems and huge leaves. Thank you.

You give no clue as to where you garden, but if possible I would move your seedlings out into the garden a little at a time to start them to harden and beef up the wimpy stems that will not support the foliage. The added light and air movement should help. Keep in the shade and only an hour to start. Al

I always transplant deep. This makes for much hardier plant down the road.

I like to plant the seedling with the complete stem underground in small pots. Then do the very same thing when I out them into the ground.

Otherwise you end up with a weak plant that will be knocked over the first bit of wind. Vegetables in particular.

@calistoga: I live in zone 6a but right now, all of my seedlings are indoors and most probably I will overwinter them and transplant them outside in early spring next year.

It's way too early to start seedlings for next year indoors in zone 6. You'll have to transplant them into bigger pots as the winter goes on, and keep them always an inch from the grow lights to prevent legginess (too long stems).

You can bury stems up to where the first seed leaves are. Have fun with it, and read up on seed starting as a hobby over the winter.

Thank you for the suggestion. I actually started pretty late for this fall's transplants hence I will just overwinter them this year for next spring.
Here's the thing: my lights are approximately 2-3" above the tallest leaves of the seedlings, but the stems don't seem to be getting TALL, but the leaves keep appearing and getting bigger and bigger, so much so that my purple palace seedlings' stems are slightly bent because of the weight of the leaves or the thinness of the stem and the leaves are resting sideways on the potting mix.

A picture would go a long ways in diagnosing your problem. Al

Ok so this is one of my Salvia seedling, which you can clearly see is bent to one side even though it is places directly beneath the light.

In contrast, this is Salvia seedling with the stem below the potting mix and the leaves seem to be doing great but I dont see a stem growing out; is this ok? And is this better the last situation?

This is my purple palace seedling and you can clearly see that the stem is bent to one side and the leaves are resting on top of the potting mix. The stem can not seem to hold the weight of the leaves? Should I bury the stem below the potting mix to rid of this dilemma?

The middle picture looks good to me too. I would bring the soil level up on the other two seedlings as well. You have plenty of room in the pots to do that. Al

They look pretty nice, tp me.
Not every plant will have a long stem. Actually, shorter stem indicates that the seedlings are getting good amount of light. Spindly , leggy seedlings on the other hand, is a sign of poor light. Thee seedling in the first picture is leaning to right. Is it slightly away from the light source? You can pile some soil around its stem and straighten it up.

You are doing fine, I must say.

Something I remember reading a couple of years ago, right or wrong, it seems to work for me, so far:
If a single stemmed plant, it can be planted deeper (can actually help a plant like tomatoes and marigolds.) If plant branches at the ground level, plant up to the branching only, not deeper-- preferably no deeper than the original position in the soil.

Well NOW, both of these seedlings are doing ok as per their stem is concerned. And I ask this for the sake of knowledge: when do you know that a seedling is ready to be transplanted outside? When the roots start showing from the bottom of the container?

When the roots start showing at the drainage holes, will work. If in doubt I just slip it out of the pot and take a look. If a number of the roots are visible reaching the pot sides and the root ball holds the mix together, that is good enough for me to plant into the garden. Al

But an important thing is: what size container are you talking about? :) I mean to ask, once your seedlings emerge, what sized container do you transplant them to? From where you transplant them outside.

Your seedlings appear to be in 4 inch pots, and that is ideal for the size to plant from, into the garden. My seeds are started in mostly 4 inch pots, with from 9 to 50 seeds per pot. For most seedlings, from the seedling pots, they go into salvaged sixpacs, and from there into the four inch again, one per pot. I am growing ornamental plants with tiny seeds. If you are doing vegetables, seed into either the sixpacs, or directly into the four inch pots. Most vegetables are sowed directly into the garden. Al