Not only is milkweed a beautiful addition to the garden, but it is the only food monarch butterfly caterpillars can eat (what is called a "host plant"). For many years, milkweed has been sprayed with herbicides and eradicated from farms, yards, and public landscapes because, although native, was undesirable in those areas, and its ecological importance was not appreciated. This reduction in milkweed has been linked to the drop in the monarch population, which has declined up to 90% in the last 20 to 30 years. Growing milkweed in your home landscape can help save the monarch butterfly population; and it's fairly easy to grow, as milkweed is virtually care-free once established and provides wonderful summer blooms that other pollinators flock to.
When to sow outside: 2 to 4 weeks before your average last frost date, or fall for spring germination.
When to start inside: 6 to 8 weeks before your average last frost date.
Special sowing instructions: With exception to narrowleaf milkweed (A. fascicularis) and tweedia (Oxypetalum coeruleum) stratification aids germination. Stratification is the process of subjecting seed to moist, cold treatment to break dormancy, which occurs naturally when seed is sown outdoors in fall. To mimic this process when starting seed indoors in spring, sow the seed into a resealable bag or a growing container of moistened seed-starting mix, cover with a clear cover, and leave the container in a refrigerator for 3 to 6 weeks, checking moisture occasionally. Then move to a warm location to germinate. More on stratification in the article Stratification and Scarification. In the case of narrowleaf milkweed, light aids germination; press seeds into the soil surface.
Sowing preparation and spacing
With exception to Irresistible Blend Milkweed (i.e., swamp milkweed), which does best in moist, even muddy clay conditions, the other milkweeds we carry are drought tolerant to varying degrees and need well-drained soil. You can improve your soil's drainage by mounding soil, adding organic material, or planting on a berm.
Water frequently to establish; however, once established, water only when soil becomes dry, as plant has a large tuberous root and can withstand drought. Irresistible Blend thrives in average to wet conditions. Tweedia thrives in drier conditions, but is not as drought tolerant as other milkweeds.
Keep area well weeded.
When 3" tall, thin to 12"-36" apart, depending on the variety.
Asclepias tuberosa thin to 1 every 12"-24"
Asclepias syriaca thin to 1 every 12"
Asclepias incarnata thin to 1 every 16"-36"
Asclepias speciosa thin to 1 every 12"-16"
Asclepias fascicularis thin to 1 every 10"-12"
Oxypetalum coeruleum thin to 1 every 12"-24"
Transplant seedlings after hardening them off, around your average last frost date. With the exception of tweedia, once milkweed plant becomes established, it is difficult to transplant because of its deep taproot. Plant it where it will not be disturbed. Asclepias spp. spreads readily through underground rhizomes, so plant in your garden where expanding growth is desired, growth can be controlled, or in containers.
Deadheading flower clusters before pods set will prolong the flowering period and prevent reseeding. Avoid spraying plants with any pesticides that could harm or deter monarch butterflies. Pinching the growing tip, removing the tops set of leaves when tweedia is young produces bushier plants. Sap is toxic; wear gloves, avoid eye/skin contact, and do not ingest.
Asclepias tuberosa and tweedia both produce excellent cut flowers. For longest vase life, harvest flowers in the morning, choosing blooms that are 1/2-2/3 open. Place in water, allowing the latex within the stems to dissipate in the water, then change the water, and change vase water frequently thereafter.
Choose Your Region
By growing milkweed that is native to your region, you ensure that blooming will occur when most needed—at the time of migration in your area—providing fuel for these beautiful butterflies. Thank you to our friends at National Wildlife Federation for helping us ensure these maps are accurate! *Tweedia is not a native to North America, and is not a host plant for monarch butterflies, however, it does provide pollen and nectar to pollinators.
Learn more about how to help Save the Monarch