I started growing these two lemon trees from (random storebought lemon) seeds a few years ago and they grew considerably over the last summer after putting them in larger pots.
Because I live in Nothern Germany where we sometimes get -10°C in the winter and I have no idea how much cold they can deal with, I take them inside in temperatures under 6°C (so basically the entire winter).
The problem is that they are getting too big to keep inside but I don't think I can keep them outside all year round. Should I cut them to keep their size within reasonable limits? Can I keep them outside all year round instead?
They are also suffering from soft scale insects (it seems coccus hesperidum is the exact name judging from images found online) that I managed to treat using an oily semi-natural pesticide. However, the insects come back after about a month. I think this is because of the adverse growing conditions inside (hot dry air from the heater and not enough sunlight in the winter).
I've bought a systemic pesticide but haven't gotten around to applying it as it needs to be applied not in direct sunlight and with no forecast of wind or rain.
As you can see in the pictures, the new leaves are unnaturally curled and pretty light compared to the older leaves. I fertilized using a long-term citrus fertilizer last spring and haven't done so again since.
I can try to provide more details where necessary. Thanks!
The smaller left one:
The larger right one:
