Hi Rogue, Here are some things I do differently... I don't like Miracle grow potting mix for starting tomatoes. I use coconut coir mixed with perlite and vermiculite... No molds grow in that. I don't get any damping off disease. I water this mix with water with calcium and magnesium supplement in it.

I put 3 seeds in 22 ounce cups with a 1/4 inch hole drilled in the bottom. I never disturb those plants again until they go in the dirt outside. I pick the best of those three plants and cut off the rest with a scissors so I don't disturb the baby roots or stem.

As soon as I have growth starting and plants slow down, I add 1 tsp of my organic fertilizer. That way I control the amount.

When I harden off the plants, I put them in the sun for 1 hr the first day and gradually increase from there.

I am sure you will get more/better advice than this, but this is a start. :)

Rebecca

"when I pulled them out to check a month later, the root system was quite small"

There is only one thing that causes that - over-watering, keeping the soil too moist causing rootlet rot and suffocation.

While I don't personally care for MG Potting Mix I can't fault it as many report excellent results with it. It is better than some of the so-called "seed starting" mixes out there. There is nothing wrong with your lights and although 75 is a bit too warm it isn't going to hurt them.

Are you per chance using peat pots prior to the yogurt containers? They only make the moisture control issues worse. And this is for sure MG Potting Mix not MG Garden Soil? They are often confused.

"leaves began to curl, got crispy, and the yellowing with purple veins became more pronounced."

Yet another sign of over-watering.

"Even my bell pepper seedlings are stunted - they're almost yellow with only one set of leaves after 2 months"

And yet another. Pepper plants are even less tolerant of water than tomato plants are.

Honestly even when some someone swears they are not over-watering 9x out of 10 they are. It is the single most common mistake made when growing from seed and kills more seedlings than all other causes combined. The only way to prove it to yourself is to force yourself to cut your inclination to water by half and watch what the improvement with your plants.

Dave

I think you are doing many things correctly. My only comment is: DO NOT use "moisture control" Miracle Grow. The polymers they use in that... holds water and makes the mix a mucky mess. That stuff is for things like hanging baskets only. Other than that...watch the watering. The plants will wilt from lack of water...and quickly recover if watered soon enough.

Did your cups have drainage holes ? If not they would get to much water.

Even with potting mix I would fertilize but at much lowe concentration, lik 1/3 strength.

Yellow leaves is indication of too much water , too little N and not enough light. But you mentioned :

""2. Put germinated seeds under brand new
4-foot T8 lights indoors immediately. Lights stay on for 14 hours a
day at least. Turned off overnight. Lights held 1-2 inches above
seedlings, moved up as necessary. Temperature kept at 75 or above. ""

What you have done should be fine. I can only suspect lack of nutrients and too much water.

Sey

The fact that you say that your plants have "NEVER WILTED", tells me that irrigation practices is your main issue. Everything else you mention sounds like you are on track. I purposely dry my plants out to a point where the leaves get wimpy. It makes for a stronger root system and a more tone plant.

The underpaid, lonesome irrigator in a nursery is actually the "grower". The "grower" is actually a manager of people. Many nurseries, large and small, never come to this realization.

"At no point did I fertilize because the Miracle Grow potting mix already contained food."

Don't trust Miracle Gro Potting mix because it's composition varies across the country. As I recall, it says on the bag that the ingredients are locally obtained and vary by location of manufacture. So, it is meaningless when somebody says they have had great results with it.

"I've started seeds in other mixes, including an organic mix, compost, coconut coir, wet paper towels, etc and same issue with all of them."

So, did you not fertilize that too?

As to the need for fertilizer, re-read the OP post. 1-2" tall plants such as the OP describes don't need any fertilizer.

Dave

Change up your treatment. Fertilize some and not others. Have a control group and a test group. While testing, document everything. Ie;water plants x, not plants y. fertilized plants x with fertilizer A. Didn't fertilize plants y.

Get all sciencey, get a lab coat and a clip board. Have fun. And good luck.

Where are you growing these plants? Some poorly vented, burned gases (natural gas) will cause stunting and deformities in some types of plants. I have only ever seen this in a tightly sealed GH with a natural gas heater though.

Why not start seeds in seed starting trays? It makes it much harder to overwater. Putting them in 32oz containers when they are 2" tall sounds like too big a pot to me too.

I also wonder about what ncrealestateguy has posted, where exactly are you growing these things, where the temp is 75 consistently?

Two things I would change.

Get seed starting mix and start in cells.

Repot into 3.5 inch pots or 12 oz cups when first set of leaves are developed. Only at this point would I use MG potting mix.

Thanks everyone for all the advice. I think you might be right and not fertilizing could be the problem. Next time, I'll do an experiment as Ignatz suggested: one half with no added food, the other half fed. I'll also use a plain seed starting medium.

As for why it's 75 degrees, I am growing inside my house (bathroom to be exact) for lack of anywhere better. Our house has poor insulation so the heat runs nonstop in the winter, causing the temp to get kind of high at times. The bathroom is also probably quite humid given people using the shower several times a day, bumping the temp up further.

I'm amazed you all think overwatering was the issue. I know how easy it is to do that, and was really stingy with water. Yes, my pots did have drainage holes. They were plastic nursery pots, not peat. Would you say that watering once a week is too much between 1-2 months old? Also: Do you think my city water might be affecting the plants badly? One source said it was high in chlorine, which seems real bad for young plants but perhaps I'm mistaken.

I'll try changing up my starting pots, too. Cells to 3.5 inch pots makes sense. Thanks again everyone.