Can Brussels sprouts and spinach be successfully grown in containers?

They can, but you will need lots of containers, especially for the spinach. You plant spinach 6-12 inches apart, and I can easily use two or three plants at a time for a salad or more if I boil it. The brussels sprouts shouldn't be too bad for container growing, but plan on having a good support system as they grow, and I would definitely use at least a five gallon pot for each plant.

I know that the Brussell Sprout plant gets about 3 feet tall so you will have to allow for the roots to spread out a bit.