Population levels of the migratory monarch butterfly (Danaus plexippus plexippus) have been declining for years, and in July 2022, the International Union for Conservation of Nature (IUCN) officially designated the migratory monarch butterfly an endangered species.
Plant Milkweed - Milkweed is critical because it is the only plant they can raise their caterpillars on
Grow Fuel Plants - asters and goldenrods are two really great examples of plants that provide additional fuel for those adult monarchs as they make the rest of the journey.
Make Your Yard a Habitat - Create places in your yard where [butterflies] can rest and find shelter from the elements. This can be as simple as piles of leaves or brush in a safe space, a log, tall grasses, etc.
Set up a Puddling Dish – since Monarchs cannot land on water to drink.
Check All Your Plants for Neonicotinoids and Other Chemicals
(BHG)