it is now day 37 since I seeded my grow cube with tom thumb lettuce seeds - the plant have been growing well, but the leaves nearer to the ground (the first ones that were born, the larger ones) seem to suffer from something.
Basically, the edge is turning brown. At the start I thought it was lack of air change, since it started when i went away for a week and I did not open the growhouse for a while. I read that this can be a problem since transpiration cannot occur at the necessary rate, and the plant develop a brownish/yellowish edge.
So I installed a couple of small fans to aerate. Now it seems that is diminishing, but still there.
Can it be something else?