Grace, simply losing older leaves does not mean the plants will die -- but you do need to find out why this is happening and fix the problem.

I'm just asking the questions people will want to know; other folks will probably give you answers.

Were the Pink Brandywines and the other varieties planted at the same time? Are they the same size? Were there any differences in when the Pink Brandywines were planted, how they were planted, when they were potted up, etc.?

Are there drainholes in the cups?

Do you water from above or from below? If from below, how long do the plants sit in the water? Do you drain the extra water from the tray?

Do you test how moist the mix is before watering? (Be aware that as the plants grow, they need progressively more water; in a container, this means watering more frequently.)

It would help if you could add a photo.

Hello! Thanks for the response. :) I appreciate your help!

All the varieties were planted at the same time and there have been absolutely no differences in when or how they were planted up or any care techniques at all. The Brandywines and San Marzanos have actually been my most vigorous growers up until the brandywines started losing the bottom leaves. :( They're all about the same size. I have 18 plants so there are of course some that have grown quicker than others but they're all in the same size range, give or take a couple inches.

Yes, there drainholes in all of the cups. I water from the top. I did not test the soil before watering, which I'm now regretting.

I'll see if I can get some pictures of them tonight! Thanks!

Here's a picture of the affected brandywine seedlings, you can see the newer leaves are still green and healthy, and the yellowing leaves, which I have no doubt will drop off eventually. They've already lost one or two each.

Here's another picture, this is of one of my san marzanos and a couple of my cherokee purples, which you can see don't seem to have the same problem. There's a yellowing seed leaf about to fall off but I know that's normal. Any ideas?

Looks like not enough light.

I don't think your tomatoes are doomed. Have you fertilized them yet? At 4-5 weeks they will start to need fertilizing in a potting mix. Lack of nitrogen will cause yellowing leaves. Also, I would check your light setup. Your plants look a bit leggy like they are reaching for light. If you can, they would benefit from being potted deep(to the first set of true leaves) and having a fan gently blowing on them. It will help stiffen them up.

There is nothing wrong with cotyledons turning yellow if the plant looks fine. Your seedlings need a tad more light but they are fine and green. Normal process.

Thanks for all the replies everyone! :)

Rawley, I have not fertilized them yet! Do you think that could be the problem? I'll be out tomorrow and can pick up some fertilizer. - How do I go about fertilizing them?

Lindalana, I know the cotyledons are supposed to turn yellow and fall off, that isn't what's concerning me. :) What's concerning me is that the first set of true leaves on my poor brandywines are turning yellow and falling off!

I am not an expert, but my seedlings looked yellowish like yours in your picture and it was a lack of nitrogen. They has been in the potting mix for 6 weeks and they has simply used up all the available nutrients. If the potting mix you used didn't have any fertilizers in it, I would say your issue, besides the before mentioned light issue, is a nutrient deficiency. Most recommend a 1/4 strength fertilizer until they are in the ground. I personally used Miracle Grow Tomato food at a slightly higher rate on accident and my tomatoes are fine. I plan on applying this strength(1/4 strength) of fertilizer every 10-14 days.

Good Luck!

Thank you soo much! I'll pick up some fertilizer tomorrow and fertilize my babies. :) I've been taking care of them for so long I definitely don't wanna lose them! I'm attached to them, haha.

I agree that they need some fertilizer as well. However, I would also say (as others have) that they aren't getting enough intense light.
They are "leggy" and that is a result of not enough intense light. Fertilizer won't cure that problem.

I just fertilized them tonight, so I'll keep you guys posted on whether or not that solves the issue! :) Thanks again for all the help!

Yeah, I'm aware that my poor babies are leggy. I've just started hardening them off outside today as I'm hoping to get them out in the garden next week buried up to their bottom leaves! My light setup isn't perfect, definitely nothing like the warm sun will be to them. I'm hoping to get a better light setup next year since once these guys are out in the garden I'm done with seed growing this year.

Surprisingly, your plants have done quite well without fertilizing up to this stage. I suppose that your starter mix must have had some fertilizer in it.

Luckily it is about plant out time in zone 7 GA. So the legginess issue can be solved by planting them deeper. I would bury them up to their first true leaves.

Seysonn, yes the mix had some fertilizer in it. :) I thought that would take them far enough along but I guess not! I really really hope that's my issue with my tomatoes dropping their bottom set of true leaves!

Yeah the weather here is getting prettier by the day, I think by next week it should be fine for planting these guys outside, just gotta get them hardened off first!

This post was edited by Aquae on Thu, Apr 17, 14 at 11:24

Hardening off: Very important step, Aquae.

I have gardened in North Fulton County , Alpharetta for many years. I remember planting out about this time of year. The LFD was April 10th, I think. But the weather warms up pretty quickly down there and tomatoes grow very fast.

Good Luck !

I would suggest 1/2 strength fertilizing, and bottom watering barely 1/4 inch up from the bottom.

Update: My seedlings appear to be doing better! They haven't lost anymore leaves and they're growing well! I'm hardening them off now! Thanks so much everyone, I'll keep you updated on their progress. :)