I was wondering if someone could answer my question about transplanting carnation seedlings. This is my first year starting any kind of seeds indoors and my carnations got a little leggy. After adding more growlights they have beefed up but some of them still have a thin week stem just at the base of the plant. My question is:

When I go to transplant, can I plant the weak part of the stem below the soil?

The seeds were planted on 3/15/19 should I move them into 4in pots? I'm on the border of zones 3-4 so I have another 4-5 weeks before I can plant them outside.

Thanks for any information!