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Old February 17, 2018   #1
FourOaks
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Default Cotyledons dont burn?

Wasnt sure where to put this. General Discussion? Starting From Seed? Undercover?

I had an interesting observation. In order to make more room under the lights, I had to move a whole bunch of very young seedlings out to the Greenhouse/Seedling house. These included several varieties, and included both Tomatoes and Peppers. All of these were in the Cotyledon stage.

After a couple days they were transplanted. I didnt offer any shade. They were in trays and setting right on the potting bench.

Even after a few days, absolutely no signs of Sun Burn. No signs of stress. They are perfectly happy. Some have already started with their true leaves. On the other hand, larger plants moved out earlier, are currently showing some Sun Burn.

Now, in my experience, Sun Burn has no real lasting effects. But I find it very interesting that these seedlings in their very early stages seem to be tougher then what I would have previously thought.

I have some flower seedlings that I need to move, it will be interesting to see what happens.

Anyone have any thoughts on this?
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Old February 17, 2018   #2
rhines81
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In warm climates, seed can easily be direct sown. Cotyledons are the initial leaves to get the plant started with the photosynthesis process - basically they stop functioning as such once the 1st true leaves start developing. The timeline for this transition is a few days, maybe 4-5 days under good conditions. Because of this they are not as prone to the change from artificial to 'real' sunlight. They basically start dying off quickly. They will remain green and grow with the plant, but their function to the plant is complete once the 1st set of true leaves come out ... they become suckers.
On onset of 3rd set of leaves, I always pinch them, because there is no purpose for them to exist as 'suckers' any longer. I could probably do this earlier, but I never have. The true leaves are more sensitive to changes because they are 'new' growth and serve a long-term purpose to the plant.
Yup, I have definitely had the true leaves turn almost solid white due to the transition, but new growth happening at that time quickly is adapted and the plant thrives.

Last edited by rhines81; February 17, 2018 at 11:02 PM.
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Old February 17, 2018   #3
rhines81
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To add to the above ... people coddle their plants merely because of the 'cosmetic' appearance of the existing growth turning white and even wilting, but truth is that the next new growth coming on will be fully adapted to the real sunlight and some of the existing true leaves will get over the transition and/or show minimal effect. Hardening off does not have to be gradual, just bring the plants in at night when then temperatures are below 55-60 and they will thrive (might not 'look' pretty, but no damage done).. New growth will prevail.
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Old February 18, 2018   #4
FourOaks
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Quote:
Originally Posted by rhines81 View Post
... people coddle their plants .. New growth will prevail.
I respectively snipped to get down to the essence of your response, and I think that sums it up. Im am just as guilty of coddling my plants.

I guess I never noticed this before, because my growing seedlings didnt demand such a mass exodus to make room for more seedlings. Over the years I have grown thousands of seedlings, but they always stayed under the lights until at least a couple sets of leaves.

The closest I ever came to that, a few years ago. I moved plants out to a smaller greenhouse that had a much different covering on it. Im not sure what it exactly was, but I had zero plants experience burn. Problem was that the mfr. wanted way too much money for a new one, when it was needed. So I switched to regular IR film.

But needless to say. Seedlings seem to be far tougher then led to believe.
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Old February 18, 2018   #5
VC Scott
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I am 5 miles from the Pacific Ocean. I put my seedlings outside in direct sunlight as soon as they sprout. This time of year they only get 12 hours of sunlight. The temperatures are cool, so they don't get too leggy. I never have a problem with sun burn.

If you keep the seedlings indoors for 6 weeks and then expose them to full sun, you will get sun burn. It occurs because you change the environment overnight. If they have always been outside, exposed to the sun, you don't need to slowly harden them off.
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