Needy seedlings . . . . .HELP!

[RomanX]

My seedlings have nice, green leaves. . . . .but with purplish undersides!

How do I correct this deficiency??

I water from the bottom (they have 1+ sets of true leaves) with a complete water-soluble fertilizer (at half strength, this is ~ 7-17-13, with micro-nutrients included).

I let them "drink up" as much as they will, starting with 20 minutes. . thinking that that amount of time would do. It did, for a day or two: then purplish undersides again! Five days later, I bottom fertilized again, but this time let them "drink up" for 30 minutes. Same result: 1-2 days of normalcy, then back to purplish undersides!

I initially choose this complete fertilizer (Jack's Classic Bloom Bust4er) last year over MG Tomato Fertilizer for my mature tomato plants. . . after resolving nutritional deficiencies while "on" MG; once cured and fertilizers switched, my plants did not develop any more deficiencies. So this year, I compared the chemical analyses of MG Tomato and Jack's Classic: while MG offered higher N, it did not list the 2 crucial micro-nutrients but Jack's Classic did.

I'm wondering now if the seedlings need the higher N . . . more so than the micronutrients.

[pmcgrady]

How cold is it in the room you are growing them in? If it's at lower temps, it will cause the plants to turn purple. It slows the growth rate down.

[bower]

Purple undersides of leaves is a sign of phosphorus deficiency - typically caused by cold because it prevents the plants from taking up P.
When I give my seedlings the cold treatment, purpling of leaves and stems is a sign they have been cold enough.
If it isn't cold, then some other reason why phosphorus uptake is not happening... deficient or maybe unbalanced ferts.
I love this explanation of phosphorus uptake factors, that is posted at Fusion's site:
http://www.selectedplants.com/OrthoPhosphate.htm

[RomanX]

The seedlings are under cool LED lights, so they don't get alot of heat that way.
The ambient temperature of the room is 70 during the day, but 65 or lower at night .

I've checked my seedlings again and the little dwarf seedlings are all green; the biggest seedlings (indeterminates) all have the purplish undersides. The middling seedlings (hybrids with an average mature height of 3 feet) are a mixed lot: some are all green and some have the purplish undersides.

[RomanX]

Now I'm REALLY confused!!!

[EPawlick]

Originally Posted by RomanX

My seedlings have nice, green leaves. . . . .but with purplish undersides!

How do I correct this deficiency??

I water from the bottom (they have 1+ sets of true leaves) with a complete water-soluble fertilizer (at half strength, this is ~ 7-17-13, with micro-nutrients included).

I let them "drink up" as much as they will, starting with 20 minutes. . thinking that that amount of time would do. It did, for a day or two: then purplish undersides again! Five days later, I bottom fertilized again, but this time let them "drink up" for 30 minutes. Same result: 1-2 days of normalcy, then back to purplish undersides!

I initially choose this complete fertilizer (Jack's Classic Bloom Bust4er) last year over MG Tomato Fertilizer for my mature tomato plants. . . after resolving nutritional deficiencies while "on" MG; once cured and fertilizers switched, my plants did not develop any more deficiencies. So this year, I compared the chemical analyses of MG Tomato and Jack's Classic: while MG offered higher N, it did not list the 2 crucial micro-nutrients but Jack's Classic did.

I'm wondering now if the seedlings need the higher N . . . more so than the micronutrients.

Can you post a picture?

[clkingtx]

I have had purplish seedlings before, and they always grew out of it and did well. If they green up after fertilizer use for 2 or 3 days, I would fertilize every 2 to 3 days. I am fertilizing with a hydroponic nutrient and am using it in nearly every watering. Especially when they are getting established, they need a lot of nutrition.