Do you have to start plant seeds in small containers?

I just transplanted my lemon tree plants. I felt like it was stressful for them. They are about 18 inches high now. I started them from a lemon I bought in the supermarket. I put the seeds into a pot that used to have basil. I think the plants have been growing for over a year (I haven’t kept track) and the small pot was way to small when I finally transplanted the plants today. The plants are very close together and eventually it’s not going to work well I don’t think with the plants so close.