Ask Mr. Smarty Plants

We assume you're talking about Asclepias tuberosa (butterfly milkweed). Even in Ohio, we would not recommend transplanting in mid-summer. this particular species is notoriously difficult to transplant, with its long taproot. It prefers well-drained, sandy soil and would probably do better if you moved it in late April, when the ground is thawed but it is not yet hot. It has been suggested that it propagates much better from seed, and you should just plant the seeds where you want the plant, because it is so hard to transplant. 

From our webpage on this plant:

Propagation

Propagation Material: Seeds , Root Cuttings
Description: The easiest method of propagation is root cuttings. In the fall, cut the taproot into 2-inch sections and plant each section vertically, keeping the area moist.
Seed Collection: Watch plants closely for seedpods in late summer/early fall. Allow seeds to completely mature before collecting seed to establish new plants in another location. A long pod is produced containing hundreds of seeds with tufts of long, silky hairs (an adaptation for wind dispersal).
Commercially Avail: yes
Maintenance: Needs to be transplanted carefully and requires good drainage. It takes 2 – 3 years before A. tuberosa produces its vibrant flowers, which appear in 2 – 3 inch clusters of orangish-red. Once established, it lasts for years, becoming thicker each year.

Asclepias tuberosa