When and How To Plant Milkweed: 5 Milkweed Growing Tips
As pollinators emerge this spring, it’s time to boost their resources with milkweed. A must-have in the pollinator garden, native species suited to our regions become valuable perennials. Gardening expert Katherine Rowe explores how to plant milkweed now for a thriving future colony.
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As conscientious gardeners, we strive to improve our corners of the world and to steward pollinators for a whole host of reasons. They pollinate our food crops, many of which require insect pollination to produce fruit. Meanwhile, they also improve the look of our ornamentals and boost seed production to expand the colony.
Insects offer natural pest control, as some beneficial species are predators for common garden pests like aphids and scale. They’re an important part of the food web for birds, reptiles, and small mammals. And when it comes to butterflies, they’re beautiful visitors who enliven the space with their fluttering.
No pollinator garden would be complete without growing milkweed. Milkweed is the sole larval host plant for monarch butterflies, whose population is in decline. It also serves a variety of other insects and caterpillars. Its naturalistic, easy-care habit and sweet ornamental bloom clusters are a delight.
While planting milkweed is broadly beneficial, growing it comes with a sort of nuanced responsibility. Not all native species are a fit for our individual sites or the pollinators we intend to support. The right kind of milkweed for our area can get highly specific, and for good reason. The availability of regional native milkweed becomes an integral part of monarch migration patterns and survival.
Here are our top milkweed growing tips for a lovely butterfly habitat!
Narrowleaf Milkweed/Butterfly Flower
Narrowleaf Milkweed/Butterfly Flower Seeds
About Milkweed
There are over 100 species of Asclepias native to North America, and the monarch-milkweed relationship is fascinating. The whole plant supports the life cycle to continue the population of the long-migrating butterflies.
Adult butterflies visit the blooms for nectar on their journeys and in their warm overwintering sites. The females lay eggs on the leaves and stems, which hatch into hungry larval caterpillars. The caterpillars feed on the foliage, leaving a defoliated plant, which we’re more than happy to share. Caterpillars may even spin their ornamental deep green, gold-lined chrysalis from the stems before metamorphosing into the winged beauties we hope to see more of.
Milkweed also plays a role in making monarchs unappealing to predators. Leaves and milky sap contain compounds that are toxic to most birds and mammals. As caterpillars feed, they, too, contain the toxic compounds. The orange coloration of monarch wings is a warning signal of toxicity to avoid.
Choose the Right Milkweed for Your Area
The most important tip for growing milkweed is to choose the right native species. Monarchs have preferences based on milkweed species and their benefits as they travel. Tropical milkweed (A. curassavica), for example, is nectar-rich but lacks essential proteins found in other species. Hairy leaves, too, make it less appealing as it matures. Native to tropical Central and South America, there’s ongoing debate and research on the topic of growing the species outside its native range and the potential impacts on monarch migration.
It’s best to plant native North American species, or wild milkweeds, as food and nesting sites for pollinators in your specific growing region. Showy milkweed (Asclepias speciosa) is a strong Western U.S. species. Common milkweed, A. syriaca, is native to eastern and central regions. The Xerces Society offers regional guides for specific Asclepias species. They also have a Milkweed Finder database to source seeds and plants.
The Best Site
Milkweeds native to your area are well-adapted to local conditions, so you shouldn’t need a lot of tips to grow them effortlessly. The wildflower perennials establish and reseed on their own in optimal conditions, especially in full sun. Depending on the species, they perennialize and overwinter in zones 3-8.
Generally, milkweeds prefer slightly acidic soils with a pH between 4.8 to 6.8. In poor compositions like heavy clay, amend with compost to improve aeration and nutrition. Most do well in well-draining soils, but some, like swamp milkweed (A. incarnata) and A. sullivantii, prefer moist situations.
Allow plenty of space for a mass planting and reseeding in future seasons. Milkweed has long taproots that are sensitive to root disturbance at transplanting, so choose a site where it can remain. The substantial roots give them good resistance to drought and heat.
The more, the better when it comes to planting a colony of Asclepias. To get on the monarch radar, plant a bunch, allow room for spreading, and partner with neighbors to do the same.
When to Plant
Fall and late winter/early spring are the best times to sow milkweed seeds. They need cold stratification to germinate and bloom, with exposure to cool temperatures for several weeks. Scatter them in fall, winter sow, or direct sow them in spring three to four weeks before your last frost date.
You can also start seeds indoors four to eight weeks before the final frost. Plan to move them outdoors as soil temperatures warm to about 70°F (21°C) post-frost.
For seedlings and nursery starts, spring is the optimal time to plant young milkweed. Wait for warm air and soil temperatures after the final frost.
Collecting Seeds
Green seed pods emerge after blooms fade, and they’re easy to spot. They have silky filaments, which birds use as nesting material. To harvest the seeds, wait until the pods are brown and dry. They’ll be slightly open or open easily under a pinch. Seeds need to be fully dry for successful germination the following season.
The easiest way to sow milkweed seeds is to scatter them in place, right from the dry pod, in the fall. Direct sowing them in the fall or winter exposes them to the chill requirement they need, and they’ll sprout as conditions naturally suit in spring.
You can also collect the seeds and store them in the refrigerator or a cool, unheated space for a few weeks to a few months. Let pods dry for a few days in a sheltered spot out of direct sunlight. Remove the filaments (try shaking them all together in a paper bag for easy separation). Place seeds in a moist paper towel or in damp sand or soil in a plastic bag for cold storage. Remove them from the fridge for spring sowing.
How to Plant
Asclepias grows from seed or young transplants. Collect seeds as they mature late in the season. Seeds grow true to type and will be genetically suited to our gardens as the successional generations develop. Collect seeds from different garden areas, or exchange with neighbors, to promote genetic diversity. You can also order fresh seeds of your native species.
Seedlings or nursery starts give new stands a jumpstart on growth and flowering. Transplant them to their prepped site, taking care not to disturb the roots.
Growing From Seed
To start seeds indoors, plan on doing so at least four weeks before transplanting them outdoors after the frost and as the soil warms.
Fill a tray with moist seed-starting mix and scatter seeds ¼ inch to ½ inch apart. Cover with a thin layer (about ¼ inch) of soil. Keep the tray in a warm, sunny spot or under grow lights. Temperatures near 75°F (24°C) are ideal for germination, and a heat mat can help maintain warmth. Sprouts should appear in a week to 10 days.
Maintain regular soil moisture through misting or bottom watering to prevent developing roots from drying. Thin to prevent crowding, competition, and poor air circulation by clipping stems at the base. Don’t forget this important tip from avid milkweed growing enthusiasts—thinning lets the remaining seedlings develop strong roots and stems. When seedlings reach three to six inches, they’re ready to move outside in spring’s warming conditions.
Transplanting
Seedlings are ready to go in the ground when they have four sets of true leaves (beyond the initial cotyledons) and are about three to four inches tall. Allow seedlings to harden off before planting. Introduce them gradually to outdoor conditions for a few days to a week, bringing them in on chilly nights.
Place them one to two feet apart to ensure good air circulation and allow for mature growth. Add a two-inch layer of mulch to suppress weeds, retain moisture, and regulate soil temperature. It also adds nutrients to the soil as it decomposes.
Maintenance
One of the easiest and surprising tips for growing milkweed is: let them be! These wildflowers grow and flower with little care, and as low-maintenance perennials, they need little gardener intervention.
Swamp milkweed flowers from summer and remains fresh into the fall. For species like common milkweed and orange tropical milkweed, cut back plants in early summer to promote a fresh flush of growth when the monarchs need it later. The trim keeps them from getting worn and woody and from altering the chemical compounds in their leaves.
Most pests don’t tolerate Asclepias toxins, but there are specialists immune to their toxins who find the wildflowers appealing. You may notice aphids flocking to stems and leaves, though they are not likely to cause damage to mature plants. In high numbers and among young and new plantings, they may cause decline. Grow a diversity of flowering plants to draw those beneficial insects to help manage pests. Ladybugs, lacewings, and parasitic wasps are immune to milkweed’s toxicity and will feed on the aphids.
Because the aim in growing Asclepias is to attract and support pollinating insects, refrain from pesticide applications. Try a strong spray of water early in the day to dislodge the pests early in the season. A strong stream may impact young monarch caterpillars, so scouting or gauging the level of infestation is advantageous.
Popular Varieties
Native milkweed varieties are plentiful, and honing in on available vendors lets us grow them in our home gardens.
Swamp Milkweed
Asclepias incarnata has showy rose-pink and purple bloom clusters on tall, three to four-foot stems. Blooms begin in mid-spring and last into fall. The species grows natively in the central and eastern regions of the U.S. and Canada in moist areas like streambanks, bogs, and pond margins.
Swamp milkweed suits wet sites but also adapts to drier soils and even tolerates damp clay. The slender-leaved, clump-forming perennial is hardy in zones 3-9.
Common Milkweed
A. syriaca is another central and eastern North American species with fragrant pink, purple, and white flowers. On shrubby, two-to-three-foot stems, the blooms emerge in clusters (you may catch their perfume even before fully open). Milkweed doesn’t only draw monarchs; hummingbirds and other butterflies find the nectar irresistible, too.
Common milkweed produces showy seedpods in fall that make unique additions to floral arrangements. The species grows across soil types and naturalizes readily in optimal conditions.
Showy Milkweed
Showy milkweed, A. speciosa, is a western species and spreads less aggressively than common milkweed. Its three-foot stems hold silvery blue-green leaves and light pink bloom clusters. Clusters reach five inches across.
A. speciosa is related and similar to common milkweed but has fine hairs on its velvety leaves and stems. The spherical blooms are crown-like on the tips of stems. It grows naturally in dry and moist sites, from savannahs to meadows to roadsides, so a pro tip is to plant this milkweed in areas similar to where you see it in the wild.
Frequently Asked Questions
Does milkweed spread?
The clump-forming perennials spread through rhizomes (underground stems) and reseed. Seedpods emerge after flowering to split open when dry. They disperse on the wind or by birds, who use the seeds for forage and their silky filaments as nest material.
Is milkweed toxic?
Milkweed gets its common name from a milky sap in the stems and leaves. It is toxic if ingested by people and animals, and sap contact can irritate skin and eyes.
