Butterfly bush gets rather large, easily 6 feet. It has a very long root that goes deep into the ground, called a taproot. Having such a long root, butterfly weed is very drought tolerant. However, forget about trying to transplant it or divide it. Its long root system makes these tasks impossible.
Butterfly weed does everything late.
It is one of the last plants to pop out of the ground in the spring. It also doesn t bloom until the very end of July. The flowers are bright orange or yellow. Butterfly weed forms interesting seedpods after the plant is done flowering. I have some lovely baby butterfly weeds growing in nooks on a cliff where you could never plant them by hand.