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purpling in under side of leaves of very young San Marzano tomato seedling

I have not grown San Marzano before but have no reason to suppose that a little purpling is normal. I have never had this issue though before with young seedlings. This one was sown on 27th Feb and pricked out into a 3 inch pot 6 days ago, so I would have expected the multipurpose compost to still have sufficient nutritional elements in it. It is a peat free one, but even so...
It's been in the same sunny spot in the house with all my other tomato seedlings which look ok. Indeed it has had the same treatment as the rest. It is a little smaller than some of the other seedlings sown at the same time, but not the smallest by any means.
Anyway I just wanted to check that this is not normal, and if it's not should I feed the plant?!?
I only have on San Marzano on the go and would like it to survive/do well. 
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  • tui34tui34 Béziers, Herault, FrancePosts: 1,960
    Evening!

    I have sown San Marzano which are not up yet.  I have never grown this variety before.

    Purple underside is quite normal.  I would have thought the compost would be sufficient in nutrients.  I don't think I would worry at this stage.

    Just keep on what you are doing and keep in touch.  I will tell you when mine are up and what they are like. 
    A good hoeing is worth two waterings.

  • REMF33REMF33 Posts: 478
    Ok, thanks @tui34 I guess it could be a San Marzano thing. As you say, it would be odd if it were a nutrition issue, at this stage.
  • Penny_ForthemPenny_Forthem North WalesPosts: 218
    Mine were sown at the end of Feb and are now in their first pots. No purpling under the leaves. Wonder if yours was in a draught and got a bit cool?
  • REMF33REMF33 Posts: 478
    I got the variety wrong. It's the Cuore di Bue that is purpling a bit, but A Resietomate is as well. (I grew the latter last year but simply can't remember if they purpled. Will make a note of it for next year.)
    Yes, draughty on the windowsill. Do draughts cause purpling? The other umpteen seedlings are ok. (Although curly leaves on one other variety that is now under grow lights.)
    If it were just the Cuore, I might think it was the variety.
    I have never had seedling problems before. The only thing I am doing differently this year is the compost, which I am not trusting at all!
    Will just have to wait and see, I suppose. 
  • tui34tui34 Béziers, Herault, FrancePosts: 1,960
    @REMF33   Ah!
    A good hoeing is worth two waterings.

  • REMF33REMF33 Posts: 478
    I found this, so maybe it was too much sunlight?

    https://greenupside.com/tomato-plant-leaves-turning-purple-try-this/#:~:text=If your tomato plants are,tomato plants to turn purple.

    I hope it's something like this as quite a few have the issue. It's clearly not variety-related. I am a bit worried about my wilting one though!
  • tui34tui34 Béziers, Herault, FrancePosts: 1,960
    I agree with @Penny_Forthem  Tomato plants often get a bit purply when they have cool conditions.   Don't worry about the colour.  Just wait and see.
    A good hoeing is worth two waterings.

  • REMF33REMF33 Posts: 478
    I am such a worrier when it comes to gardening ;) Which is ironic, because the actual gardening is a source of serenity.

    Thanks both.
  • REMF33REMF33 Posts: 478
    I just googled the leaf curling of the Big Mama hybrid variety. (Both plants are now doing it.) Apparently they are prone to it. Most likely culprits: over watering or too cold. They are now in the propagator with grow lights in the house, so 20C at least (which surely should be high enough? Assuming the thermostat is working. I have my doubts!) and will use the moisture gauge more assiduously.
    I really must write all this down on my spread sheet for next year!
  • Pete.8Pete.8 Billericay, EssexPosts: 8,499
    If your pants are on a windowsill they will get quite a chill at night and that is the most likely reason for the purpling.
    Windowsill is fine during the day (but too much sun can cause problems too), but at night there will be a very cold draught coming from the window. Put your hand on the window sill at night (when radiators are off) and you should feel the cold air falling onto your hand.
    If you can move your seedlings away from the window sill over night, then I'm sure they'll be fine.
    They'll probably be fine too even if you leave them there :)
    I've had the opposite recently - some of my tom seedlings have got yellow leaves - the temp in the propagator in my g/house has been well over 30C on some days over the last week, but they will recover too.
    It's just when seedlings are young they get affected more.
    Knowledge is knowing that a tomato is a fruit.
    Wisdom is not putting it in a fruit salad.
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