Leaves purple underneath new seedlings

[buniot]

Hello,

I have new seedlings (Beefsteak, Mortgage Lifter BI-Color, Aunt Ruby's, Purple Cherokee, and Camp Joy), that are about three weeks old now. The leaf undersides are a purple color but the tops of the leaves are just fine.

I am using organic seedstarting mix from gardners supply and the APS system to water from bottom up.

I have not fertilized yet, but do have Neptune's Harvest Seaweed/Fish Emulsion. Is this purple color a result of a deficiency or some other issue. Thanks in advance.

Tom

[bcday]

It's not a problem. Sometimes it's caused by cool growing conditions but in itself it's nothing to worry about. I would go easy on any fertilizer if you think you just have to do something -- use it just once and at 1/4 strength or less. The roots of young seedlings are easily burned by fertilizer and are not easily re-grown.

[buniot]

Oh, thanks very much for your input. I am so new to growing from seed, I thought it may be deficient in Phosphorus like a full-grown mature tomato plant.

[Gobig_or_Gohome_toms]

I had seedlings last year that had the purple leaves for the first time in 4 years of growing from seed and as soon as they got planted out they soon lost the tint so i would not worry about it.

Craig

[buniot]

Well, I put a very,very weak dose of fish emulsion on one of them, kind of as a test to determine if the purple goes away or not. It was so weak that the color of the mixture was lightly colored. I am interested to see if the purple color goes away. Thanks for all the input everyone!

[dice]

It is a phosphorus deficiency symptom, but it does not
necessarily mean that the soil does not have enough
for the seedling (although a lot of seed starting and planting
mixes have no N-P-K to speak of, so it could be deficient).
In cool temperatures, the seedlings can show those symptoms
even if the planting mix has enough phosphorus for the
seedlings to get by until plant out. In that case the symptoms
go away once the weather warms up.

I like to dust a little something in the seed starting mix when
potting up from seed starting cells to newspaper pots. A pinch
of kelp meal and a pinch of mild, slow-release, balanced organic
fertilizer mixed into the seed starting mix below the seedling
works well for me. It breaks down fast enough to be useful to
the seedling yet slow enough not to burn it.

The bottom-watered, ultra-mild dose of fish emulsion should
work too.

Other things one could try: put a tablespoon of rock phosphate
or bone meal in a quart of hot water, let it sit overnight, bottom
water with it. Only a tiny bit of it will dissolve in that time, but
it may be enough to treat this. (Guano tea or a pinch in the
seed starting mix at pot-up time would probably work, too,
but guano is quite potent, and it would be easy to overdo
it.)

[Salty_Dog]

Interestingly i had a whole tray of cells grow very slow and have vivid purple under the first two leafs.
They were raised in commercial seed raising mix and at 22 degrees C in a warm room with a fluorescent light over them for 16 hours.

A month later i started some of the same seeds in a self watering seed raiser made from a soft drink bottle, using the exact same seed raising mix and just placed it on the window sil.

The ones in the soft drink bottle were never purple and within 2 weeks were bigger than the others that were planted a month before.

Now 2 weeks on again, all the soft drink bottle seedlings are planted out and the cell tray seedlings still haven't reached a suitable size to plant out, even though i ended up removing the artificial light and placing the cell tray on the same window sil.

Both the same seeds from the same packet, both the same seed raising mix, both watered about the same, although the soft drink bottle has the wicking effect.
Yet amazingly the difference in growth, with no purple on the seedlings in the soft drink bottle.

All i can think is the air flow provided by the soft drink bottle is greater than the cell tray.