plants grown in the house under lights... need to be HARDENED OFF to the intensity of sunlight ...

explain how you do this.. and we can speculate from there ...

in other words.. i am suggesting that you are sunburning the heck out of them.. and the leaves generated under indoor lights ... can not acclimate to sun .... but when new leaves are produced.. appearing in the sun ... they are fully acclimated ...

when i did seed ... first they went in the garage.. where they only got a little light when the sun hit them late in the day .... then a week later.. moved them to full bright shade.. then a week later.. into part sun .. then into blistering sun ....

how do you do it???

ken

It can also happen with little plants you buy in flats that were already in direct sun, so I don't think it's a sunlight issue. Sunburn usually is just browning, not this purple/red thing.

Usually happens to me in containers with fresh potting soil, to pansies, verbena, angelonia. I think it's an overabundance of some nutrient, or chemical reaction in fresh potting soil that makes some component temporarily unavailable. I've also wondered at times if tap water has something to do with it.

Is {{gwi:8010}} the look you're talking about, renee? The caladiums seem unaffected although they took FOREVER to come up. Here are {{gwi:8011}} {{gwi:8012}} more examples. And here it is on {{gwi:8013}}.

It's been happening to me this year, while it has not happened last year. I agree that it must be a soil issue. I grow mine from seed under supplemental lights, but the seedlings get winter/early spring sun whenever it is available, outside when it is above 60F at high noon. We're talking anything from the first leaves on. Last year, my lobelias, browalias and impatiens did fine, and I just planted them right out when the weather warmed up enough. No leaf color change before or after.

However, I had the leaf discoloration and growth stall on all my plants this year. If I give them some fish fertilizer, that seemed to encourage a spurt of new green growth. I think it may help to "flush" out/leech the soil. Perhaps it was this year's batch of Miracle Gro. I guess I'll have to change to something else, but it's hard to find anything in a smaller amount in retail stores.

It has always happened to my lobelia, and the leaves stay a more purple color all summer. I had assumed that it was a reaction to the light spectrum of the real sun as opposed to my fluorescent lights. It was very evident in several different kinds of lettuce seedlings I planted out early this spring. There were hints of red on the leaves under lights, but once they got out in the real sun the red/purple became much more pronounced. It is definitely not sunburn, the lettuce is supposed to look this way. I think the "growth stall" is just the adjustment to transplanting into the garden. The roots all of a sudden have room to spread and thats where the energy is being spent.

indoor sunlight thru double pane windows with r factor gas between .. is not really sunlight at all ....

even thru just a single pane of glass ..

it hard for me to imagine that seed starting media ... can go sterile and lack nutrients.. in the few week it takes to start the seed and get them outdoors ... unless a full drench system is washing everything out of the soil.. or they are being left in the pots for multiple years ...

i wish OP would come back and tell us how they are hardened off to sunlight and temps .. going from the cozy house to the outdoors ... in Alaska ... i wonder which zone in Alaska??? i know they have a bizarre z7 up there ...

ken

Thanks to everyone for all the follow ups!

ken_adrien: All my plants are grown in a greenhouse with about 90% light transmission. No artificial lights. I assumed years ago that it was sun burn, so I spend an excessive amount of time hardening them slowly to the sun outside of my greenhouse. 1 hour 1st day, 2 hours 2nd day..... so on. Our Zone here is a solid 2. Most 3's work also.

Purpleinopp: Yes, the photos 1 & 2 are what I am talking about, only mine are darker in color. I too have wondered about the soil or water. I plant many (hundreds) of flowers, so they usually do not have new soil, but our water here is really cold, maybe that's it. I wish I could find an exact answer!!

franeli: I think you may have the answer! Would you recommend that I add phosphorus at the time of transplant?

Renee, I would like to know, too. I've experienced this intermittently over the years and it's always been a mystery. It was 65-70 most days when I put these pots together at the end of Feb., 45-50'ish at night. Pansies like cold, petunias & verbena like heat. All did this purple thing. The verbena and petunias I potted alone. But I always put caladium bulbs when I do potted pansies. The caladiums come up and shade the pansies, are much taller and more interesting during the heat. Then the caladiums die back and the pansies come alive again and use the moisture so the caladiums don't rot before I get around to digging them up. Anyway, the caladiums in these pots are growing the correct colors, growing well but took longer than usual to poke through.

The plants I bought were outside, not in a greenhouse. I ran out of pots with dirt from last year, so bought more, 2 different kinds from different places. Now, 3 months later, the plants that turned purple and are still in their pots are the same size as when I bought them. I took most of the worst ones and put them directly in the ground about a month ago. Those plants have all turned back to their regular color and are getting bigger now. All plants in the ground & in pots have had tap water since this area is missing 6" (according to average) of rainfall since 4/1.

ya kinda left out the fact that you are a semi-professional greenhouse grower ... dont ya think ...

as such.. you ought to know that a soil test will tell you what is lacking in your soil.. before you go making amendments ...

z2!!!! ... yikes.. how long is summer.. 3 weeks... lol ..

good luck

ken

I think I found the problem. I found this on the Plant and Soil Sciences eLibrary website. I've never heard of this site but it came up when I Googled, "low phosphorus damage in plants". Here are a few lines copied from the article.
1. Plants deficient in phosphorus are stunted in growth and often have an abnormal dark-green color. Sugars can accumulate and cause anthocyanin pigments to develop, producing a reddish-purple color.
2. Plants may be phosphorus deficient due to cold temperatures which affect root extension and soil phosphorus uptake. When the soil warms, deficiencies may disappear.
I bet because of our cold night time temps (it's still getting into the low 40's at night here) and our really cold water, this is what's happening.

I was researching Potassium deficiency. I found that it may be causing the purple discoloration I had on my pansies when I lived in San Francisco, but it may have been a fungus, becausing using a fungicide would general help the issue.