Monarch caterpillars feed exclusively on the leaves of milkweed, the only host plant for this iconic butterfly species. As such, milkweed is critical for the survival of monarchs. Without it, they cannot complete their life cycle and their populations decline.
Indeed, eradication of milkweed both in agricultural areas as well as in urban and suburban landscapes is one of the primary reasons that monarchs are in trouble today.
The good news is that planting milkweed is one of the easiest ways that each of us can make a difference for monarchs. There are several dozen species of this wildflower native to North America, so no matter where you live, there is at least one milkweed species naturally found in your area.
Planting local milkweed species is always best. You can collect your own seed or purchase seed or plants to add to your garden, or any landscape in your community. Three species have particularly wide ranges and are good choices in most regions: common milkweed (Asclepias syriaca), swamp milkweed (A. incarnata), and butterflyweed (A. tuberosa). The latter two are highly ornamental and widely available via the nursery trade.
Note: Tropical milkweed available at many retail nurseries is not native to the U.S. However it has naturalized in the Southeastern U.S. Science is discovering that its long bloom time may have some detrimental effects on monarch migration and possibly be a source to spread disease within monarch populations. If you do have tropical milkweed in your garden, it is recommended to cut the plant back in the winter months to encourage monarchs to move on to their natural overwintering sites.