I am growing tomatoes from seed this year for the first time. My plants are under LED lights and are about 6 weeks old. The underside of the leaves is purple and some of the leaves are turning yellow. The leaves are kind of shriveling and just generally not looking great. Does anyone know what I might be doing wrong? Am I watering too much or too little? The temp inside is in the 60s or 70s now. They're getting about 16 hours of light per day.

I'm going to move them out in a few weeks (live in Central MA) but am worried some might not make it.


  • 2
    I don't think you're watering them enough, the soil looks dry and the fibrous peat pot shows no dampness - follow Stormy's instructions re watering below
    – Bamboo
    Commented May 8, 2018 at 1:46
  • And do not plant them directly in the garden without acclimating them first. That takes at least 2 weeks. We've got lots of stuff on how to acclimate when changing the environment of a plant from indoors to the out of doors to the covered patio from the out of doors to the indoors or greenhouse or grow room.
    – stormy
    Commented May 8, 2018 at 1:50

1 Answer 1


Purple on the leaves could be indicative of one of three things:

  1. Phosphorus deficiency. Cold temperatures can make this worse.
  2. A variety that is supposed to get anthocyanin on its leaves. In this case, there's no problem.
  3. Sulfur deficiency (most people might not think this makes the leaves look purple, but I kind of think they look a little purple and translucent—not as purple as with the other two items listed here, though); your plant doesn't look like it has sulfur deficiency, however.

Yellowing (if the veins are yellow, too, and it's not just the edges of the leaves that are yellow) is probably indicative of nitrogen deficiency. If it's just the edges of the leaves that are yellowing, that's usually potassium deficiency. Yellowing leaves with green veins is usually something like magnesium deficiency. Overwatering can cause yellowing (and a host of other issues), but it doesn't cause purple leaves.

Too much of certain nutrients or soil amendments can also cause yellowing, sometimes (e.g. too much wood ash).

It sounds like you probably used seed-starting mix (which is what you should have done) and the plant finally needs fertilizing. However, it shouldn't be dying if that's the case. If it's dying, something else is wrong. I'm guessing something may be off about the soil. It sounds like the plants are getting plenty of light, which is great. The plant in the picture doesn't look like it's dying, though.

Just water the tomatoes when the soil dries out on top. Most people probably water their pre-transplant tomatoes every two to three days or so, if they're in those plastic cells. If they're in larger/smaller containers, and depending on the soil, things may be different.

  • Thanks Initially they were in jiffy seed starting mix, and when I transferred them into 3” pots I put them in miracle gro potting mix. I water them from the bottom every 2-3days when the pots feel dry. Do you think I should fertilize them?
    – Steve M
    Commented May 8, 2018 at 1:18
  • Yes, definitely. Commented May 8, 2018 at 1:19
  • 1
    YES...those babies are a bit beyond what they should have been given a few weeks ago. They are just showing you they need some chemistry so they can make food, carbohydrates for themselves for all their processes and repair and growth.
    – stormy
    Commented May 8, 2018 at 1:25
  • 3
    Why do you water from the bottom, Steve M.? Could you find the bag of miracle gro potting soil and make sure that no fertilizer (NPK) has been added? Do not fertilize until you know that that potting soil was only potting medium WITHOUT fertilizer. Water from the top, please. Allow to drain, keep pots elevated off of saucer or surface using bits of 1/4 " tile, broken tiles, dump out the saucer if there is a saucer. Find out what is in your potting soil otherwise, yes, they look like they need fertilizer. But not until you know what is in that potting soil.
    – stormy
    Commented May 8, 2018 at 1:29
  • 1
    Yeah, if you water from the bottom, there could still be fertilizer in the top of the soil. Most of the roots might be at the bottom. I haven't tried bottom-watering. So, I can't say what works there. Commented May 8, 2018 at 1:31

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.