The Ultimate Guide to Growing Milkweed for Monarch Butterflies
Help monarch butterflies thrive by growing the one plant they need the most: milkweed.
Why Grow Milkweed Plants?
Monarch butterflies are rapidly declining due to loss of habitat and use of pesticides. Planting milkweed is the most effective way to help because it is the only plant that sustains a monarch through each of its life stages. It also produces a chemical that makes monarchs toxic and bitter-tasting to some of their predators.
“The bottom line is, if milkweed disappears, so will monarchs,” says Laura Lukens, who works as a national monitoring coordinator for the Monarch Joint Venture, a partnership of American federal, state and other organizations. “Home gardeners have a huge role to play in providing habitat for monarchs, pollinators and other wildlife. Residential properties have the potential to contribute many thousands—maybe even millions—of acres of habitat.”
What is Milkweed?
Milkweed, scientifically called Asclepias, is a huge genus, with 73 species native to the United States and more than 100 species across North America. It’s the only plant that hosts monarch caterpillars. Common milkweed has a wide native range, but it might not be the best choice.
Which Kind of Milkweed Should You Grow?
Select milkweeds native to your region. Common names vary wildly, so use botanical names when you’re researching. Since milkweed species have varying needs for sun, water and space, pay extra attention to growing requirements.
It’s helpful to have a diverse selection of native milkweed and flowering plants, but avoid tropical milkweed (A. curassavica). Although it’s easy to grow, tropical types host a parasite that infects and harms monarchs. It may encourage monarchs to stop short of their full migration and increases the risk of parasitic transmission.
Check with native plant specialists to learn how to minimize problems year-round, such as cutting plants back to a few inches tall in fall and winter.
Best Milkweed Plants for Your Region
Monarch Joint Venture recommends these regional milkweed species.
Northeast/Midwest: common (Asclepias syriaca); swamp (A. incarnata); butterfly weed (A. tuberosa); whorled (A. verticillata); poke (A. exaltata).
Southeast: butterfly weed (A. tuberosa); whorled (A. verticillata); white (A. variegata); aquatic (A. perennis); sandhill/pinewoods (A. humistrata).
South Central: green antelopehorn (A. viridis); antelopehorns (A. asperula); zizotes (A. oenotheroides).
Western, excluding Arizona and California: Mexican whorled (A. fascicularis); showy (A. speciosa).
Arizona: butterfly weed (A. tuberosa); antelopehorns (A. asperula); rush (A. subulata); Arizona (A. angustifolia).
California: Mexican whorled (A. fascicularis); showy (A. speciosa); desert (A. erosa); California (A. californica); heartleaf (A. cordifolia); woolly (A. vestita); woolly pod (A. eriocarpa).
How to Grow Milkweed Plants
The easiest way to grow milkweed is to start with plants instead of seeds, tucking them into the ground after the danger of frost has passed. Starting milkweed from seed is tricky.
Most seeds need a period of chilling called vernalization and stratification to germinate and then flower. In cold climates, plant seeds directly into the ground in autumn.
Starting Milkweed Seeds Indoors
If you want to start the plants indoors, place seeds between moist paper towels inside a sealed plastic bag or plant the seeds directly into peat pots covered with a sealed plastic bag.
Chill in a refrigerator at least 30 days. Plant cold-treated seeds in a moist seed-starting potting mix. Place the pots under a grow light or near a sunny window. Warning: Seedlings may take a long time to emerge or not grow at all.
If the seedlings make it, start to transplant the 2-to-3-inch plants with the intact rootball after the danger of frost has passed. Most milkweeds have long taproots that hate to be disturbed. A seedling may lose its leaves after being transplanted, or it could die. Check out these 5 butterfly nectar plants that can be started from seed.
Where to Plant Milkweed
Some types of milkweed spread more aggressively than others. To contain the plant, grow it in a raised bed or container and remove the pods. Or plant it only where it can run freely. Milkweed does not need to be fertilized.
Wear gloves when handling milkweed, because the milky sap may cause skin or eye irritation. In large quantities, the sap may be toxic to livestock or pets.
Will Aphids Hurt My Milkweed Plants?
Milkweed may attract aphids and other insects.
“While a high concentration of aphids on your milkweed may look bad, these insects are not necessarily causing harm to monarchs,” Laura says. “Unless they are in extremely high density, there are usually not enough to kill the plant.”
Not sure if you’re dealing with monarch eggs or aphids? Learn how to tell the difference.
Because chemical pesticides or insecticides also kill monarchs, the best option is to remove the pests by hand, cut off stems with lots of aphids or simply allow nature to take its course. Check out more natural ways to eliminate insect pests in your garden.