Germinating Seedlings Fried in Full Sun?

[ThirdCoastBorn]

I've become quite adept at starting seeds during the wrong season, indoors under less-than-ideal conditions, shuffling them in and out all day to harden off Since I routinely read that certain species like pines NEED to start under full sun for the best development, have been excited to start new batches of Pinus nigra, Ulmus pumila, & Punica granatum nana. I've germinated these species at 85%+ several times this winter and look forward to comparing at season's end the progress of the 'early starts' vs. the 'ideal starts' so to speak.

After pre-treating as required, 12-cell trays (black) were exposed to bottom heat and lights for about ~24 hours (these germinate quickly); yesterday morning, I noticed a few starting to pop above ground so moved them outside to full sun. I checked moisture/watered as necessary a few times throughout the day -- the ones that had already sprouted didn't get scorched or dry out, but all the others (multiple seeds per cell) appear to have died on surface contact. Anyone have experience with this? Does "full sun for seedlings" not REALLY mean FULL SUN, or is there an upper temperature limit it typically applies for? High reached 79 yesterday...

 

[Anthony]

Tropics here -

Pines are germinated under sun from 6 a.m. until 1.00 p.m

Most other seeds can handle the above.

Factor in, paint tested in Miami and Arizona fails down here.

For seedlings -
Soil mix for pines is 1/3 commercial Canadian peatmoss / perlite
and 2/3 silica based gravel.

These days 2 waterings around 7.00 a.m is enough to handle
the breeze and the 45 % humidity.
Good Day
Anthony

 

[Shibui]

all the others (multiple seeds per cell) appear to have died on surface contact.

What does this mean?
All my seeds germinate in full sun (8am- 5pm) and grow just fine unless they dry out or get some fungal infection. The existing seedlings survived so I would look at possible alternative problems for these deaths.
Any photos of the live and dead seedlings may give clues to the problem.

 

[sorce]

Couple more freezey nights is all, that can be counteracted with a cover.

Do it!

Sorce

 

[ThirdCoastBorn]

I apologize for letting my reply slip through the cracks -- it's been sitting drafted in another open browser tab! Unfortunately, I never took photos of the two trays I was referring to, but had inspected the roots of the fried seedlings -- did not appear diseased in any way (no fuzziness/discoloration). My understanding is that if it was a cultural issue (overwatering), the other seedlings within the cell (that had already broken surface under artificial lights) would also have damped-off?

FWIW, I came across this section in a Forestry Service document on container tree production (Vol 6 "Seedling Development), even if the document appears generally outdated:

"Temperature extremes. Because of their limited root system, young germinants are very susceptible to drought and direct heat-injury to the succulent hypocotyl tissues...Symptoms of post-emergence damping-off are more obvious: the young emergent falls over due to a constriction at the surface of the growing medium. If the cause is a fungus, the hypocotyl and root
appear discolored or decayed. Damping-off also can be caused by heat or chemical injury; in this case, the hypocotyl is damaged right at the surface of the growing medium but the root will not be decayed."

However, since no one else seems to experience this problem, I'll assume there was another unseen cause at hand. Not a big loss by any means, just hoped to know if it was risky for the future!