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Tomato seedling leaves turning yellow?

last year

I just noticed that some of my tomato seedlings have their first set of true leaves starting to turn yellow, with a few dark green spots clustered around the veins. The underside of the leaves on all the plants are a dark purple color, which I can't seem to get a straight answer on whether that's a problem or not.
I've got them under a grow light which I keep turned on for about 14 hours a day. I water them every other day for the most part, and I just started adding liquid fertilizer diluted to 3-1-2. I've only done this once so far but was planning on doing it once a week. Another thing to note is that the room I'm keeping them in averages around 67 degrees, and I've been a little worried that this is too cold.
Do any of these things seem like an obvious red flag? I recently lost all my pepper seedlings to damping off disease so I don't want my tomatoes to die too :( Any help would be greatly appreciated.

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Comments (3)

carolb_w_fl_coastal_9b
last year
Might be the cool temps. Have you tried warming things up yet? It can take awhile for the plants to show improvement, tho.
daninthedirt (USDA 9a, HZ9, CentTX, Sunset z30, Cfa)
last year
Sorry, no way will 67F hurt tomatoes. They'll grow faster if hotter, but they will do just fine at room temp. That's the temperature I always grow my tomato seedlings. To the extent you just started fertilization, I have to suspect that it may have been a nutrient deficiency issue, especially if the soil has no nutrients. Now, commercial seed-starting and potting soil usually does contain fertilizer, though usually in VERY tiny amounts.
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Have you fed them anything? Jiffy mix has zero nutrients. Give a boost with seedling fertilizer. Not seeing top-growth doesn't mean there's no growth. Right now your seedlings are developing root systems and those are far more important to a seedlings outcome than too much topgrowth wth nothing to support it below the soil. Outdoors you're still experiencing cool nights and the sunlight hours aren't long. You shouldn't be seeing a lot of topgrowth, that would be unatural. Patience is a virtue, don't rush the development of your seedlings.
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I'm wondering if you have over-done it with the fertilizers. The best cure of this is a good flush with clear water to dissipate the ferts. More is not better with ferts. Here's a link that may help. FWIW, my garlic is strong and hardy right now, I rarely water the beds this time of year. I have some tomato plants that are over-wintering well. I just throw in a handful of homemade compost from time to time, top with some soil or potting mix, depending if the plant is in the raised bed or in a container, then water it all in. Good luck, I hope they all pull through. Here is a link that might be useful: Tomato Symptom Chart This post was edited by marymcp on Sun, Jan 12, 14 at 10:08
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Over watering can definitely cause yellowing. While still in the cups let the soil dry out before watering. The legginess is probably because they need more light than they are getting in the window. And, they're probably large enough that they could use a gentle, light fertilizing, if you haven't done so already. Once you get them in the ground they will not be so prissy and demanding. I know that you are putting them outside when the weather is nice. That's good, but start them out in the shade for short periods of time (like 15 minutes), and very gradually expose them to sunlight for very short periods of time until they get used to it. Otherwise, the leaves may get sunburned and bleached out. Ask me how I know. :-)
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More than one thing causes this but first I would check for spidermites. Place a piece of white paper under the leaf and tap the leaf. If it is mites you should see tiny pepper size spots crawling on the paper.
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Labradors
last year
Have you potted them up yet? If not, it might be time. If you haven't, you could use some potting mix with nutrients included. The temperature is great, and wouldn't be causing the purple leaves.

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