Hello,
We have established Butterfly Bushes and do not want to destroy them. We also want to help the butterflies. If we plant Butterfly Weed between the established bushes will that help? I read the bushes don't feed the caterpillars and the weed will.

Phoenixville, PA... Just above Philadelphia...

Nothing wrong with planting a nice bed of asclepias tuberosa (butterfly weed).
With any luck, the monarchs will use it as caterpillar food.

Also... consider other host plants for the other local butterflies...

Hi & welcome! Sounds like a great idea. The difference you mentioned is "host" plants vs. "nectar" plants. A butterfly host plant is one on which eggs are laid, and the caterpillars that hatch out of the eggs eat the plant. Different butterflies use different host plants. Monarchs require Asclepias (butterfly weed/milkweed) plants as host plants. Monarch butterflies, and most other butterflies, can use a much wider assortment of blooms to get nectar.

There are various species of Asclepias that should grow in your area, not just A. tuberosa. You can browse Asclepias plants in the plant database on this site. Some of them have zone info, some not. If you get stuck, somebody in your area should be able to help out.
https://garden.org/plants/sear...

According to the garden hardiness zone lookup tool on this site, you are in Z7.
https://garden.org/nga/zipzone...