Well, I have tried growing sweet peas in containers and trained it to grow up a bamboo pyramid, but these aren't called topiaries. Living topiaries are normally plants that have a long life, and sweet peas, being annuals are most certainly not. They do well for a short time in containers but as summers come, their pots tend to dry out more often, the plants come to seed too fast and they start getting aphid infested and tired looking by mid summer. Sweet peas are sensitive to heat and need to remain cool. Once the blooms set in, you'd need to deadhead them as often as you can. And try as you might, the leaves and stem start turning yellow as teh days get hotter. Believe me, even if you tried pruning them as often as you can, they won't look neat and tidy. Howeve,r having said all that, by all means, though, try the plant as a container plant, but just keep in mind this plant is an annual and won't last as long.

Sweet Peas are very heavy feeders to begin with. They are difficult to grow in containers as they have very deep root systems.I fill up my planting rows with coffee grounds and crushed egg shells all winter, they seem to like that. Good luck.