If you’d like a smaller bush to host your Tiger Swallowtails, Magnolia virginiana, Sweet Bay Magnolia is a good choice. It wants to be a multi-stemmed bush and with a little judicious pruning every year, you can keep it to a manageable size. Note that they can get to be 30 feet tall, so don’t be afraid to cut. Besides Tiger Swallowtails, I’ve even had Giant Swallowtails lay eggs on this.
Butterfly Gardening 
I would love to grow this, but I’d have to keep it at about 6 ft. tall. Is that possible without ruining the look of the plant? Thanks, Dana