Want to attract butterflies more types of butterflies and support biodiversity? Plant "host plants". A host plant is a plant an insect needs to complete part of its life cycle. Often, this is a specific plant the insect has co-evolved with to lay eggs on so the hatching larva can feed.
For instance, milkweed is the host plant of the monarch butterfly. As the leaves and the sap within the milkweed are toxic, monarch caterpillars have evolved the ability to eat the leaves without getting ill. The toxin accumulates in their bodies so when they are eaten by other animals, such as birds, the animal gets sick and learns to avoid them. The Viceroy butterfly, which has similar coloring and markings to the monarch but does not eat milkweed and is not poisonous, benefits from the predator’s learned behavior.
Use the below guides, plant lists, and suppliers to get started.