| Hi, Sorry to let you down, but if would like to make your meadow closer to a "native habitat", by planting species native to the mid-Atlantic United States (your home region and mine too) then Verbena bonariensis is not a good choice. Verbena bonariensis originates from Argentina and Brazil. It often becomes invasive (displaces other species by self-seeding and rapid growth) when introduced to a new home with a favorable climate, such as ours. For example, see this link: http://www.floridata.com/ref/v/verb_bon.cfm The next link, Missouri Botanical Gardens, also mentions invasive tendencies: http://ridgwaydb.mobot.org/kemperweb/plantfinder/Plant.asp?code=A111 And your own comment, "I have seen it when it's happy in a home garden take over", confirms the invasiveness. If you are looking for wildflowers to attract butterflies, there are a great many native alternatives. Here, for example, is a "top fifteen" list of "top native nectar plants for adult butterflies" from a garden center with a yearly butterfly exhibit in the Washington, DC area. (I have planted a number of these, and can testify that they really attract butterflies.) By the way, if you (like the butterflies) enjoy the purple flowers of the Verbena, you will see that there are many shades of PURPLE on the following list: 1. Apocynum cannabinum - Dogbane or Indium Hemp. White flowers. Dogbane family. 2. Asclepias syriaca - Common Milkweed. Lavender. Milkweed family. 3. Asclepias incarnata - Swamp Milkweed. Deep lavender to rose. Milkweed family. 4. Asclepias tuberosa - Butterfly Weed. Bright orange. Milkweed family. 5. Eupatorium (several species) - Joe Pye Weed. Lavender. Composite family. 6. Echinacea purpurea (*) - Purple Coneflower. Purple, of course. Composite family.
(* not a true native to the eastern coastal plain and Piedmont region; native a bit further west) 7. Vernonia novaboracensis - New York Ironweed. Intense purple. Composite family.
(other mid-Atlantic native ironweeds are Vernonia gigantea - Giant Ironweed, and Vernonia glauca - Broadleaf Ironweed. I highly recommend all of these as an alternative to the Verbena if you are looking for bright purple flowers that attract swarms of butterflies). 8. Cephalanthus occidentalis - Buttonbush. White, button-like flowers. Madder family. [9. Cirsium (species) - Thistle. Composite family. I am putting this one in brackets because there are several very weedy non-native species, so you would want to make sure you have seeds of the correct species before planting. Other posters on this forum can provide more information about Cirsium.] 10. Solidago (species) - Goldenrod. Yellow, of course. Composite family. The most common species, especially S. canadensis, are probably already well established in your meadow; you could seek out some of the less common natives for planting. 11. Aster novae-angliae - New England Aster. Deep purple. Composite family. There are a number of native Aster species, with flower colors from white, pale blue, and lavender to deep purple (with the New England Aster at the purple end). 12. Bidens (species) - Tickseed Sunflower. Yellow. Composite family. 13. Liatris (species) - Blazing Star. Purple. Composite family. 14. Monarda fistulosa - Wild Bergamot. Lavender. Mint family.
(Also consider Monarda didyma, Beebalm, with brilliant scarlet flowers.) 15. Pycnanthemum (species) - Mountain Mint. White. Mint family. | 
