Lemon tree leaf defect

Hi!

I searched in Internet a lot, but still couldn't find what is wrong with my lemon tree.

What cause could be for this type of leaf defects? Some leaves on some branches start to dry out from side.

 The funny thing is that in 2012 summer leaves became yellow. So I started to fertilize it. Leave green color returned and as surprise on October 2012 tree thrived new leaves. So I continued to fertilize slightly. Next surprise was that now on January 2013 tree thrives new leaves again. But some of those from October dry out from sides. Also 1/2 of leaves slightly curve down.

No obvious insects. Fungus? Overfertilizing?

Where is it it situated-I'm guessing indoors somewhere-near a window,radiator?

Both. The tree is on window sill, which is above ratiator. Outside is winter (~0°C ... -10°C).

Then I think it is too dry an atmosphere-those leaves look as they got typical scorch-have you been misting it or foliar feeding it ?-that would explain the brown dots where it has dried on the leaves

As for the brown edges again to dry and the sun has been shining on them through the window

If there is nowhere else for it-then when it goes outside the new leaves should be ok

In the meantime try standing the pot on a tray of moist pebbles or grit-that will increase the humidity around the plant and help ease the problem

Yes, it is very dry air in the room. Probably old leaves suffered from insufficient water, because was thriving new leaves.

I am not misting or foliar feeding the tree.

The new leaves are ok.

Will try to add water in plate under pot. The pot is on small legs so tree won't get additional water from plate.