I don't want to fertilize too soon, but I might feed a weak solution tonight...the stems are dark purple. Any ideas?

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I would go ahead and fertilize withe weak solution, 1/3 strength (from the bottom ) . Your seedlings look normal, otherwise.

Purple stem is very common. But it also may indicate Phosphorus deficiency and cooler temperatures.It can get quite cold at night by the window.

If you are using fluorescent lights, there is no need for direct sun. Keep the light about 1 inch from the seedling.

It takes about one week to germinate. And during the second week the growth is very slow.

Question: What was/is your seed starting medium ?

Sey

The medium is peat moss (zero nutrients). The lights are mounted to a scrap of plywood suspended 1-2 inches above the tops of the seedlings. And it may look like I have the tray wrapped in plastic, but it's just a barrier to keep the cats from snacking or walking over the tray. The seeds sprouted from about 3/5 to 3/16 (peppers a little slower).

The natural light that they do get is shaded a little from the mounting board right now. Only the row closest to the slider gets any real sunlight for now, and those seedlings are leaning ever so slightly toward the artificial light.

I'm starting to think the cotyledons are sunburned from the water left on the leaves after misting. I'm just worried that the true leaves won't grow before the cotyledons have dried up...the first true leaves were poking up maybe 2mm last night.

I keep tricking myself into thinking these are older than they really are (24days). I was quite satisfied with my results until I saw the slightly browned cotyledons last night. I'll have to take a pic of the "burned" leaves tonight...the OP pic is from about a week ago, and I guess misleading. I'll be back home in a few hours...

the spots weren't there last night, so maybe these got too wet for a few days?

It's hard to take a pic of such small leaves!

These are the San Marzanos...one is a faded green. I'm hoping the true leaves will grow FAST!

Pure peat Moss, zero nutrients ... NO WONDER !

Seeds have some initial store of nutrients to germinate, grow a tiny root and few leaves to get the system going. But at some point the seedling will need external source of nutrients

So I would take them out, plant them in a potting mix and fertilize. with a tomato fertilizer ( w/Ca and Mg)

Sey

I raised the lights a few inches and sprayed diluted fert. on the tomatoes. Fingers crossed...

They are too small to pot up quite yet. I was hoping to pot up this week or next before they seemed to...stop...growing!

Correction to the medium: it is the Pro-Mix peat-based all purpose...orange compressed bale, has a little perlite, sphagnum, neutralized, etc., so it was supposed to have a slow release fertilizer. It's what I had on hand and needed to get the seeds germinated before a vacation. I haven't had issues with the peat drying out...stays moist too long if anything. For the last week, I haven't bottom watered until the entire cell is becoming dry to the touch. I know not to let the peat mix dry out too much, which is why I started misting the top, and I think that mix has a conditioner.

I was waiting for the true leaves before fertilizing, and the off color leaves looked more burned than yellowing last night. The true leaves poking out look nice and green. Will carefully feed and pot up when they get going :)

Just laid a thermometer on the flat...I'm curious how chilly it gets near that door.

Thank you!

My first guess was the peat medium... way too acidic. But now you say it is a mixture from Pro Mix, so its probably not that. I would still take a pH reading though.

I used to grow commercially in Houston Tx, and have never seen a plant get sunburn from having water on the leaves... and we watered all times of the day, sun or not.

I wouldn't spray even diluted fertilizer on young seedlings. The cotyledons have no stoma to absorb it and it can easily burn them. Better to apply it directly to the soil so the roots have access. And those seedlings can be transplanted easily even at this stage. Getting them out of the peat pots would be my priority.

But yes, there is a great deal of difference between straight peat and Pro-Mix. So the peat pot moisture wicking problem is causing the yellowing IMO.

Dave

Yeah...sorry about the confusion on the mix. I do use straight peat when mixing for SFG raised beds outside and was away from home when posting. I was thinking it must have been peat, which is in the same size/type bag. I had the Pro-Mix for mixing into potting mixtures.

I did spray directly on the "soil" when I added the fertilizer, trying to avoid the leaves., and followed with a spritz of distilled water to rinse any overspray. I'd have added it from the bottom tray, but I watered from the bottom 3-4 days ago and the bottoms of the cells were still moist to the touch.

I think my lights were too close. Lights off: 65F at soil surface (air temp, not soil temp)/Lights on: 85F at soil surface...that's after I'd lifted the lights about 2.5 inches. I just did a bit of Googling for t5 lights too close to seedlings and found this quote "T5's burn hotter than T12s, especially at the ends." I don't think it's a coincidence that the cells that had the burned-looking cotyledons were at the corners of the tray.

I think they'll survive...like I commented last night, the true leaves poking out are a nice dark green. I think they were stunted a bit from heat or whatever the cause and starting to drop the cotelydons a bit early.

I'll get them potted up by this weekend, for sure. Thanks for all of the advice!!

Do you know how many people complain in these fora about problems with plants grown in Pro-Mix but blame everything but Pro-Mix? A rational person would blame Pro-Mix before blaming anything else. The key word to ponder is "inconsistency." You can't use someone else's success with Pro Mix as evidence that all Pro Mix is good because the manufacturing process is error fraught. Maybe, a disgruntled worker urinated into the lot. Who knows?

"peat medium... way too acidic."

You are just repeating an popular myth. I bet that you never tried an unneutralized peat based medium. I know that this is a myth because I have been successfully growing tomato and other seedlings in a mixture of 2/3 peat moss and 1/3 perlite or 1/3 parboiled rice hulls, without added lime or other added alkaline substances, for over 10 years.

Under the user name, struwwelpeter, I posted this:

http://forums.gardenweb.com/discussions/2005610/how-to-easily-supplement-fluorescent-with-incandescent-light

I suggest that you peruse my post and pay attention to

1. my potting media and fertilizer

2. the number of naysayers telling me that my potting media is too acid

3. the size and health of my tomato seedlings 36 days after planting seeds

And, I should add that my potting media is cheaper than any premix that you can buy. Now, the key word to ponder is "suckers."