So I learned the hard way about overwatering the butterfly weed, and I need some advice on how / when / how often I should water. Can someone give me some pointers? I REALLY want these awesome plants to work for the long term. Thank you!!

Butterfly bushes are pretty tolerant of being dry- I think I've only watered my newbies 3 times since I planted them in April. The key is to not let them dry out at the beginning, while their roots are establishing. I used 1/2 gallon each time I watered because I had smaller bushes, watered them maybe a week's time apart for 3 weeks, then I just let them be. If you get a lot of rain now, don't bother watering because we are getting into the end of the season and they really need to establish roots before winter. Hope that helps.

I hear so many plants named butterfly weed...which/ what specifically do you have?

When I grow asclepias tuberosa from seed, I usually do not water.
As dry as it is here in the sandhills, I did once lose an entire patch of seedlings due to extended drought.... but in Chicago, I would not expect to ever need to water this plant.

Just realized this was butterfly weed, not bush! Sorry about that- I just assumed the bush because of how Che described it.

Oh sorry for the confusion. Yes I'm talking about the weed (asclepias tuberosa). So, I just won't water it at all then? Makes sense since its native...I amended the soil so it drains better and is a little rocker. Added some sand, pebble, and crushed gravel (but not too much of any.)