I'm trying something new out. I'm growing a few varieties of Japanese Maple seeds in a grow tent. The two that I will mention in this post are Green Japanese Maple and Sango Kaku. The tent is setup with a nice exhaust system which keeps the air cycled in the tent. A 6" fan inside the tent running on low speed which I keep high in the tent to prevent the breeze for hitting the seedlings directly. I also have an LED Grow Light which I keep at a far distance from the seedlings. The humidity in the tent hovers between 50 - 65% and the temperature hovers between 78 - 80 F. My current problem is that the leaves on my seedling are rolling downward. The leaves are not crisp they are fleshy, soft. I will post pictures. I need to know what is causing this. From the research I've done it might be too much water or too much light. My current light cycle is 12 hours on and 12 hours off. I have a PAR meter and the current reading at the canopy is 300 micromoles. Four days ago when the leaves looked healthy, I positioned my light closer to the canopy at 950 micromoles for two days. Once I saw the leaf issue I backed off the light to 300 micromoles. I also stopped watering in case I was over watering. Here are my questions: 1) Why are the leaves rolling downward? 2) Does anyone know what PAR level is best for Japanese Maple seedling? 3) As the trees get a few months older should the PAR levels increase and if so to approximately how many micromoles? I know many varieties of Japanese Maples like early sun and shade in the afternoon. I've done a lot of searching and found no articles that mention PAR levels for Japanese Maples. Any help to answering any of these questions would be greatly appreciated. If you have any questions for me ask away.
Leaves may do this sort of thing (1) when the roots aren't getting enough oxygen. It may be what is happening with your seedlings. IOW I would reduce the watering frequency. It could take a couple of weeks to see a positive response. I don't think you need to adjust the PAR level as the only the portion of the light falling directly on the leaf is utilized for photosynthesis. The light in areas where there are no leaf surfaces presently simply goes to waste as it is adsorbed by potting soil and the pot holder. More leaves will utilize this wasted light until, of course, leaves begin overlapping (in which case the light is fully utilized but not all the leaf area is). Most maple leaves become adapted to whatever light level they are in (e.g. shade adapted). If you subsequently increase the light level, they often respond by creating an anthocyanin shade that give the leaves a reddish hue. It can take many weeks for the photosytems to adjust and for the red shading to go away. Red leaved varieties also do this, becoming greener in lower light conditions. IOW, watch the leaf color.
