Purple Leaves - is this bad? (picture)

[NewGardenerCanada]

My seedlings have started turning purple on the underside of their leaves. I've read online that this might be because the room is too cold. They are sitting in a sunny window during the day so maybe I should move them to a warm room during the nights when it gets a bit drafty? Anything else that could be causing this?

[alexmac]

hi new gardener
Purple underside of plant leaves generally indicates a phosphorus deficiency which could be from a soil that is too cold , too wet, too dry, for the bacteria that feed the plants to be busy, so plant is not able to get phosphorus or maybe, possibly a general phosphorus deficiency in the soil.
this is common in seedlings when cold, keep warm and just moist and they normally grow ok.

[PunkRotten]

I wouldn't worry about it right now. I think your plants need more light though.

[NewGardenerCanada]

Thanks for the feedback!

PunkRotten - I took this photo at night... the seed tray is sitting in a sunny window during the day. Did you say that they need more light because of the way the seedlings look or because of how dark the picture looked? Just curious!

[lily51]

Tomatoes are heavy feeders. I've not had one this size get pull I shall, but when it happened e 's it can be a phosphorous deficiency. A'll so, tomatoes need magnesium, which not all fertilizers have.
Does your starting mix have any nutrients in it? If not, a mild solution may be needed now.

[rainbowgardener]

It is not uncommon in indoor grown tomatoes and will likely correct itself once they get planted in the ground.