📌 Quick Summary (TL;DR): Brown, Crispy Seedling Leaves
- 🍂 The Problem: The leaves on your tomato seedlings are turning thin, brown, and crispy (like parchment paper) before eventually falling off.
- 🔎 Common Misdiagnoses: Growers often mistake this symptom for bad potting soil, overwatering, or a Potassium (K) deficiency (since the plant pulls mobile nutrients from the lower leaves to save the growing tip).
- 💡 The Real Culprit: According to veteran growers, this specific pale, crispy die-off is a classic symptom of severe light deficiency.
- 🛡️ The Fix: Run your grow lights 24/7 for about 5 days to help the plant recover. After that, keep the supplemental lights running for at least 18 hours a day until it is time to plant them outside. If they are on a windowsill, push them as close to the glass as possible.
Good evening Lyudmila and everyone!
Can you help me figure out what’s wrong with these tomatoes? My niece sent me these photos and wrote:
“I left some on a shelving unit (with standard LED grow lights), and put the others on the windowsill. But in both spots, the leaves on most of them are drying out, turning thin and brown like parchment paper, and falling off. The soil is commercial bagged mix (Terravita). I water them with plain water when needed, haven’t added any fertilizer.”
I had this exact same thing happen with that specific potting soil (Terravita) last year. There was absolutely no root development in it. Unfortunately, that brand has been very hit-or-miss lately. Tell her to try transplanting two of them into a completely different brand of soil, just to rule out a bad batch of potting mix.
My opinion—she is overwatering them. She needs to gently aerate/scratch the topsoil and let them dry out.
Irina, there’s not enough info here. Are they already in 16 oz (0.5L) cups? If so, it means she potted them up recently. Did they look sick before she potted them up, and if so, how long ago did this start?
My first impression is that the seedlings actually look decent structurally—the stems are thick, they aren’t leggy, and they have breathing room. BUT they are extremely pale. That means either they aren’t getting enough light, they lack nutrients, or the roots aren’t absorbing nutrients. And the leaves literally look burned.
The lower leaves are yellowing. Lower leaves turn yellow because of a lack of mobile macronutrients—the plant sacrifices the bottom leaves to move those nutrients up to the top, because the plant’s main priority is keeping the growing tip alive.
It doesn’t look like Nitrogen deficiency. Not Phosphorus either. Not Magnesium or Manganese. That leaves Potassium. It looks like Potassium deficiency. There’s also Zinc deficiency, but if it were that, the new young leaves at the top would be tiny and deformed too. So if it’s not an actual disease—I would try applying Potassium Sulfate both as a foliar spray and a root drench.
This is a severe lack of light.
For the ones on the shelving unit, she needs to turn the grow lights on 24/7 for about five days. After that, keep the supplemental lights running for at least 18 hours a day until it’s time to plant them outside.
The ones on the windowsill need supplemental grow lights too. As a last resort, she can line them up in a single row pressing them as close to the window glass as possible. That will help, assuming you get some actual sunny days.
Iskorka: “I left some on a shelving unit (with standard LED grow lights), and put the others on the windowsill.”
Which direction do those windows face? Could you get her to take a wide-angle photo showing exactly how they are arranged on the shelf and the windowsill? And what exactly does she mean by “standard LEDs”? I agree, the main cause here looks like a severe lack of light combined with sowing them too early.
Valtwelve: So if it’s not an actual disease—I would try applying Potassium Sulfate both as a foliar spray and a root drench.
Never take diseases or nutrient deficiencies that happen to mature plants grown in the garden/greenhouse and try to apply them to indoor seedlings. Seedlings do not get diseases, other than Damping Off (and you really have to mess up your watering to get that).
Literally every other problem with indoor seedlings is a physiological disorder caused by the grower messing up the environment (light, watering, temp).
They are cold white 15W LED strip lights. We saw a guy on social media recommending these specific strips for seedlings.
Thank you everyone so much for the advice! I passed it all on to her!
Irina, you can clearly see in that new photo that the seedlings are absolutely miserable under those lights, they look depressing. Aside from fixing the lighting, she also needs to re-evaluate her watering and feeding schedule.
Those lights are clearly not enough. If it were my setup, I would replace those strips with actual full-spectrum E27 socket grow bulbs (yes, they are more expensive, but read the reviews first). And I would definitely re-sow a few of them; under proper lighting, new ones will catch up and grow much faster and healthier. Also, whenever possible, she should be carrying them to a bright window or balcony to get natural sunlight.
