You can grow sweet peas in containers or hanging baskets but a bigger, in-ground growing space is usually better. The size of the flowers is proportionate to the size of the roots, and these plants like lots of room—both width and depth. Containers at least 18-inches deep are recommended: a smaller size can inhibit growth. If this doesn’t matter to you, use smaller containers. They are beautiful flowers either way. Just be sure to keep up with your watering so they don’t dry out. Some sweet pea seeds are marketed specifically for growing in containers so look for those.