I have a small citrus australasica in a pot. It is indoors at present due to cold weather & frosts. The leaves at the outer edges of the plant have started curling up and although still looking green they are dry and crumble. I can find no traces of a pest infestatation. The soil is moist but not soaking wet
Certified GKH Gardening Expert
This is the natural process indoors. The lack of humidity and direct, unfiltered light causes it to go into a semi dormant state. You can supplement light with about 200 watts of horticultural lighting, and either put a humidifier next to it, or spray a few times daily with a fine mist. This will help out.
Here is an article for more information: https://www.gardeningknowhow.com/edible/fruits/citrus/growing-citrus-trees-indoors.htm