I´m new to gardening and have a question. I have a borage plant that is heavily infected with black lice. I think I have managed to kill most of the lice with nettle water and milk, but the plant is still not healthy. Is it a good idea to cut it back down to a small plant, or will it stop growing this season if I do? And should flowers that are done flowering be picked, or will the plant drop them by itself?
You can remove any yellow or brown plant material, but leave anything that is green.
As far as the flower, you can leave them or you can remove them. Either is fine and will not hurt the plant. Some people like to remove them to keep the plant looking more visually appealing.