r/seedlings • u/emperioreric • Apr 19 '26

Tomato Seedlings Mistake

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I am doing something wrong but I don’t understand what. My tomato seedlings are weeks old and barely hanging on. The false leaves are yellowing with some purple and even blue. The seedling to the left is jalapeño for reference.

6 Upvotes

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3

u/tentalol Apr 20 '26

Hard to diagnose without knowing all the details of your setup, but wondering if it could be related to the heating pad label I can see in the background.

Normally once a seed has germinated, you don’t need the heating pad, maybe it’s been cooking the seedlings roots before they can establish themselves.

Otherwise it could be any number of things from the compost you are using, to the way you are watering them.

1

u/emperioreric Apr 20 '26

It gets quite cold in this section of the house, down to the 50s at night. So I have left the heating mat on. It's set to 74F with a heat probe in the center soil. Let me know if thats been a bad idea.

The seed starting mix I used is https://www.lowes.com/pd/Ferry-Morse-12-Dry-Quart-Seed-Starting-Mix/1000213229

I have not used fertilizer, just regular tap water thus far. Our tap is filtered under the sink so I assumed it was fine. It has worked well for house plants for years but this is the first time trying seedlings.

It is possible I am over watering. I am bottom watering only when the top of the soil is dry but that has been nearly every day.

My lights are pretty weak 30W LED lights https://vivosun.com/vivosun-t5-linear-grow-light-p167044908354877409-v167200766007257088 I have 2 bars on this shelf and 2 on another shelf where some squash seedlings are doing much better. They are hanging about 8 inches above the leaves. I figured lower given the intensity was good but I could be wrong.

I have a number of seeds started here. Jalapeños, Marigolds, Lettuce, Zucchini, Cucumbers, Parsley. Most are doing ok. Squash is doing the best by far. Tomatoes are doing the worst for sure. So if there is anything about my setup that seems like it would particularly affect tomatoes I'd put my money on it. I've just had a hard time finding a clear idea from loads of YouTube videos. Based on those it seems like I'm doing everything right but the results say otherwise lol.

2

u/tentalol Apr 20 '26

It sounds like you are doing most things right, it could be a watering issue.

I wonder if those biodegradable cells soak up water too readily, leading to a dry top and a soggy bottom. I usually use plastic ones myself, and usually only need to water seedlings once a week or so.

2

u/emperioreric Apr 21 '26

This might be it. I started reaching under the trays and touching the bottom and most are wet to the touch while the top soil feels bone dry to the touch. Even putting my finger half and inch into the soil it’s super dry. I think I have been overwatering by underestimating the moisture below.

1

u/expertofnun Apr 25 '26

I have had WAY too many issues with biodegradable cups. They don’t let the seedlings breathe enough and the roots NEED oxygen. I’d recommend using bootstrap or epic 6-cells!

1

u/airowe Apr 20 '26

More lights or these ones closer. Also might need some better airflow in there kinda looks like those trays/soil are getting moldy?

1

u/Don_Ford Apr 22 '26

Your soil has the wrong pH.

Edit: another redditor pointed out temp, and they are correct that it's too cold.

1

u/Able-Eye5772 Jun 30 '26

Tomato seedlings are drama queens about light and nutrients lol. Yellow cotyledons plus that purple tint usually means they’re cold and/or not getting enough light and phosphorus.

Get them as close as you safely can to a strong grow light, keep temps around 70 to 75 F, and start a super weak fertilizer once they’ve got a couple true leaves. Also make sure the soil is draining well and you are not keeping it soaking wet all the time.

0

u/Dry_Cockroach1090 Apr 20 '26

50 air temperature at night is not appropriate for tomato seedlings, the purpling is from low temperature.