If you have space for a tree or two, here are a few recommendations which I grow or have tried.
Hop Tree – Ptelea trifoliata – host for Giant Swallowtails. These trees are hard to find and you may have to start them from seed. Note you can also plant Rue for Giant Swallowtails which is obviously a lot smaller. Height and Spread is up to twenty feet.
Tulip tree – Liriodendron tulipifera – host for Tiger Swallowtails. Up to 90′ tall and 50′ wide.
Hackberry Tree – Celtis occidentalis – host for Hackberry, American Snout, Question Mark and Comma. 60′ tall and 60′ wide. I keep mine trimmed back to 7 feet tall.
Willows – host for Red Spotted Purple and Viceroy. Size depends on the variety. I have never been able to raise caterpillars on willows.
Pawpaw trees – Asimina triloba – host for Zebra Swallowtails. These are rare in my location and I have given up on this tree. It also sends up suckers so be prepared for plants all over the area.
Butterfly Gardening 