Stem cracking is not really abnormal nor threatening, though it is a little odd that you're seeing it in most of your plants. There are a host of diseases that will discolor foliage, but nutrient deficiency is a possibility. I should ask if you have applied any fertilizer to your pots. Is this a commercial sterile potting mix you're using?

Good questions from Dan. It appears that the stem crack is the least of that plant's problems though. We need many more details about its nutrient supply, its age, its soil composition, and what weather it has been exposed to.

Dave

I haven't applied any fertilizer. I used peat pods to start out then transplanting with a commercial potting soil that said it was good for seedlings. I am planning on working my soil with manure, Epsom salt, egg shells, and compost when I plant them in the garden next week. Is fertilizer on top of that necessary?

I am currently in the process of hardening them off, so yesterday was a 7 1/2 hour day in the shade. Today they will start on a little sun time. It has been really windy and yesterday the coldest temperature while they were outside was 55 degrees F. Could the wind and cold temp cause the stem crack?

Questions:

Peat pellets or peat pots? Did you strip off all the netting or pot before transplanting them? If not there are root development problems

Potting soil, not potting mix? Soil compacts in small containers causing more root development problems and most contain little to nutrients so the plant is starving now.

Yes they definitely need feeding. Most all seedlings do once they develop their first set of true leaves and it has to be supplied by the grower, usually first in a 1/2 diluted form of one of the many well balanced liquid or water soluble ferts.

" I am planning on working my soil with manure, Epsom salt, egg shells,
and compost when I plant them in the garden next week. Is fertilizer on
top of that necessary?"

Probably. The additives you list supply very little in the way of nutrients. Epsom salt has some magnesium, manure is low nutrient and depends on an active soil food web to supply nutrients, same applies to compost as it is a soil amendment not a fertilizer, and egg shells have nothing of any use until they decompose so might help some next year.

So if you don't add any fertilizer of any kind then the plant survival will all depend on whatever nutrients might be available in your native soil.

You plant shows purpling of stems and leaves which is a sign of phosphorous deficient, pale leaves meaning insufficient nitrogen, and the splitting is likely due to inconsistent soil moisture levels.

Please feed it.

Dave

Thanks, Dave! I'll go pick up some fertilizer today.

Yes, seedlings that size in generic potting mix need some fertilizer. BUT don't use too much. The fertilizer instructions will come with recommended dilutions for potted plants. I'd take that recommendation, and dilute it another factor of two or three before applying. Your plan for amendments to your garden bed sound mostly reasonable. But I'd forget about Epsom salt, unless you *know* your bed is magnesium deficient. Epsom salt isn't a magic fertilizer. It's basically magnesium and if your soil doesn't need magnesium, it's not going to help (and might hurt) if you put it on.

Dave is right about phosphorus. The color of your leaves reminded me about phosphorus deficiency, which is why I asked about nutrients. Any generic fertilizer will have phosphorus.