Heres a photo of the setup:

Nice set up, and I love your pots... I want to try those but they are too expensive to get to Canada.

Maybe if you turn the LED off and take pics you would get more responses, it's hard to see what is going on in the red light.

Also I wonder why you need the LED, natural light is always best. Is it too shaded in there?

thanks for the advice when i have a sec ill try to get some natural lit photos. The reason for the led is that i was told by many people - including some serious botanists - that i have no chance of getting citrus to fruit from seed in NY without the addition of light during the winter. Also, while on some days the sun does get inside the greenhouse nicely, it depends on the location of the sun because there are trees on some sides that shade it.

ok here are pics without the leds on - just natural sunlight.

Any ideas/suggestions?

LED has a very small focused intensity, maybe the leaves are burning because they are in a spot that the led light is shinning on too brightly?? i know LED doesnt put out too much heat but it looks as though that set up has some UV spectrum led's on it maybe you are giving the new sensitive leaves a sunburn, IDK just a thought maybe buy a piece of acrylic sheet and paint it with like 25% white acrylic paint mixed with 75% water to diffuse the light more and make it less intensely focused in a particular spot?? what degree angle are on the LED bulbs?? usually led have like a 30degree angle and if you have them too close the light will be too focused on one particular spot and can burn the leaves. or you can try putting it on a timer and have it on for 30 minutes off for 30 minutes see it that helps. is this happening on all the seedlings? or on the ones directly under the light? not on the ones on the outer edge of the light??

Soil too wet?

Zomick I think you should start a new thread to attract more attention and title it "need greenhouse help" or something like that. People get excited about checking out greenhouses and then you will get the advice you need from the greenhouse experts.

I do agree the tips look burned... perhaps by the cold at night? Also I think it would be important to get the pots up off the ground.

wow, thanks for all the great replies - what an unbelievable forum! i hear the need to re-categorize as greenhouse help. I am a total newbie at any gardening/growing. Also, Thank G-d I am not the one invested financially in the greenhouse/light which were indeed expensive but i do take care of the upkeep (and electric bills!). Unfortunately for our needs the citron cannot be grafted but must be grown from seed and we are willing to wait - the whole thing is really an experiment to see if we can achieve success. Part of the reason for the exaggerated lighting/pots etc/ is too see if we could speed up the maturing process.

Most of what i have done came from reading up on the net about citrus care - but i do realize that most of the info is tailored for mature trees and not seedlings. I also saw some conflicting stuff - for example one site said that seedlings do need fertilizer and another said that in general leaving them under constant light from the beg might speed the growth stage.

I am going to tone down the light, cut back on the feeding and see if i can introduce some more moisture to the air (the fan in the back is really just for air circulation - it doesnt cool and is on low throughout the day.

When do seedlings start to need fertilizer?

the lights might be a contributing factor, it does seem like it is the ones directly under the lights that are suffering - i recently raised it much more and the trees are starting to grow normal leaves on top again. Thanks everyone for being so helpful!

esilviu - seems like great info i had thought of root temps but cannot think of a way to control them in the pots, any suggestions?

Seedlings will need fertilizer just use at 1/2 strength for the first few months most labels on fertilizer will have a directions for mixing for seedlings, if not mix at 1/2 strength to be sure. what are the low temps during the day and night in the greenhouse?? just putting the pots off the ground and on a shelf or rack of some sort a few inches off the ground will increase root temps as the ground will be significantly cooler than the ambient air in there. i think the leaf burning is due to the light id raise the light up, and either cut back on how many hours you run that light or cut back on the intensity of the light by placing a painted acrylic sheet in front of it to diffuse the light. although if there is UV spectrum bulbs on that light that might be a factor as well, because things like clouds and such do not block UV light so even if your green house doesnt seem like it is getting light from outside it may still be getting high amounts of UV spectrum light and then you have UV bulbs on that led fixture so you may be giving the sensitive leaves a sunburn. id just raise the light fixture higher raise the pots off the ground and adjust the light back to less hours and some intermittent time off during the day.

thanks joshinya that interesting - there are one or two uv bulbs on there i think and the light comes with the ability to increase or decrease the intensity of those bulbs separately. do you think its only the uv bulbs giving the sunburn, or should i decrease intensity on all the spectrums?

id try cutting back the intensity on just the UV bulbs for now, for say like 3 weeks and see if the problem corrects itself, if you still have the leaf burn issue then cut back on all the bulbs but im almost positive you have just too intense UV spectrum which is causing the leaf burn, as far as any other fertilizer/nutrient effects i cannot be sure. correct one problem then move onto the next but doing as others have suggested with raising root temps will allow better uptake of nutrients and all problems may correct themselves within a month or so.

Ok, so i just checked the temps on the soil at root level in all the pots. They are from 20 - 22 Celsius. Its a little warmer now than it has been outside, and Im sure the temps drop at night. But I still do not know of a good way to raise the temps in these pots. Elevating seems like it wont do much, they are already on decking that is raised from the ground and doesnt get too cold. Also the smaller ones are elevated a foot from the decking already and has the same soil temps. any ideas?

heat mats or heat wire can be used to increase the temperature of the pots.

For your air-pots, heat wire seems more suited since it can be coiled around each pot.