Problems with Scots Pine

Hi
I planted my scots pine from seed last november. They made good progress at the start. However they are now still only a couple of inches high in mid Sept. The needles are turning brown. Do they have some kind of infection or is this due to another reason. I have replanted them into bigger pots which made no difference.

help please

 

I've grown quite a few different pines over the years from seed and some do seem to grow away quite quickly and then stall until the folowing spring. The lower needles going brown and falling off is quite normal, as long as there is still the growing point they'll be fine. Mature pine trees also shed many hundreds of 'old' needles....