Common milkweed (Asclepias syriaca) is a native herbaceous perennial that appeals to butterflies—especially the monarch butterfly. Asclepias is the only plant family that serves as the host plant for monarch butterfly egg laying. The monarch larvae, the hatchling caterpillars, feed exclusively on milkweed leaves. Without milkweed, there can be no monarch butterflies.
Common milkweed grows quickly to two to four feet in height. It has a narrow vertical growth habit and thick, long, oblong green leaves that grow to about eight inches.
Plant seedlings in the early spring after the danger of frost has passed and direct-sow seeds in the ground in the late fall. Once established, milkweed spreads rapidly by self-seeding if seed pods are not removed. In late spring to mid-summer, fragrant clusters of pink-purple flowers appear. Milkweed's leaves and the milk-like substance within are poisonous, except to monarch butterflies.
|Common Name||Milkweed, common milkweed|
|Botanical Name||Asclepias syriaca|
|Plant Type||Herbaceous perennial|
|Mature Size||2 to 4 ft. tall|
|Sun Exposure||Full sun|
|Soil Type||Any well-drained soil; tolerates clay soil and poor, dry conditions|
|Soil pH||4.8 to 7.2|
|Bloom Time||June to August|
|Flower Color||Pink, mauve, white|
|Hardiness Zones||3 to 9 (USDA)|
|Native Area||Eastern United States|
|Toxicity||Toxic to humans and animals|
Common Milkweed Care
Plants in the milkweed family are the single most important source of food for the threatened monarch butterfly, and planting a patch or two in your landscape is an important contribution to the continued existence of the species.
Plant common milkweed about 18 inches apart; their rhizomatous roots will quickly fill in the space between plants. Your biggest maintenance challenge will probably be in containing them. Asclepias syriaca spreads both via seeds and rhizomes, forming colonies.
The flowers produce warty seed pods two to four inches long that split when ripe to cast many fine seeds to the wind. You might want to remove the seed pods before they open to reduce spreading. If you let the plant go to seed, they will sprout in distant corners of your yard (and beyond), thanks to the silky appendages that allow the seeds to waft on the slightest breeze. They are rather like the seeds of dandelions in this regard. Common milkweed might not be the best choice for formal perennial borders because of its tendency to get weedy and spread aggressively. It's better suited for naturalized areas like open fields and meadows and butterfly gardens.
Common milkweed prefers full sunlight. It grows best in an open area where there are six to eight hours of sunlight per day.
This plant prefers dry to medium average, well-drained soil. It tolerates dry conditions, infertile soil, and rocky conditions.
Common milkweed does not need watering except in the driest conditions. Water deeply, giving the plants between one to two inches of water, then wait until the top inch of soil is dry before watering again. Overwatering common milkweed can result in a lethal fungus.
Temperature and Humidity
Common milkweed tolerates a wide range of temperatures and humidity. But because it's native to eastern parts of the United States, it will not do well in extreme and extended heat or humidity.
There's no need to fertilize common milkweed plants. Common milkweed tolerates poor soils.
Types of Related Milkweed Plants
Over 100 native species of milkweed plants are found in the United States, including common milkweed. In addition to common milkweed, here are some of the most popular types of milkweed within the Asclepias genus, which grow to different heights and bloom colors:
- Butterfly weed (Asclepias tuberosa): one to two feet tall; light orange blooms native to the northeast United States
- Swamp milkweed (Asclepias incarnate): four to five feet tall; mauve, pink, or white blooms native to the northeast and southeast United States
- Sandhill milkweed (Asclepias humistrata): one to three feet tall; pink, lavender, or white blooms native to southeast United States
- Showy milkweed (Asclepias speciosa): one to three feet tall; rosey-purple and pink blooms native to the western United States
Propagating Common Milkweed Plants
Propagating common milkweed by taking cuttings can be easier than dividing rhizomes because milkweed tends to grow deep taproots, which can be tricky to dig up. With cuttings, you can create new plants in a short period of time which is ideal if you want to get a quick start to creating butterfly garden. Here's how to propagate milkweed plants via cuttings:
- Take cuttings of common milkweed in the middle of the summer when stems are green. With a sharp, sterilized garden cutting tool, cut stems that are four inches long. Choose green stems with three to five leaf nodes.
- Remove the lower leaves of each stem and keep the top two pairs intact. Coat the bottom of the stems with a rooting hormone.
- Place stems standing up in potting medium that is an 80/20 mix of perlite to peat moss.
- Place pots in a shady cool spot out of any direct sunlight while the stem is forming roots. Keep the soil evenly and continuously moist.
- Transplant the cuttings into the ground within six to ten weeks.
How to Grow Common Milkweed From Seed
Common milkweed seeds scatter on their own right before the coming cold seasons so they can naturally encounter cold stratification. You can also scatter seeds directly in the ground in the fall so they can go through this process, planting them about one inch deep in the soil.
Be aware that when you start common milkweed seeds indoors, thel cold stratification process to increase the germination rate takes 30 days, so plan to start that process sometime in March. Here's how to start common milkwood seeds indoors:
- Although this step is optional, if you want to increase your seed germination rate, stratify the seeds first. The easiest way is to wrap seeds in a damp paper towel which is then put in a zippered plastic bag. Put the bag in the refrigerator where they will be undisturbed for about 30 days before planting in peat pots.
- Fill peat pots 3/4 of the way with seed-starting potting soil; moisten the soil until it is just damp.
- Place one or two seeds in each pot. Cover the seed with a 1/4 inch of soil.
- Water the seed from the bottom up. Put the peat pots on a flat pan and add 1/2 inch of water to the tray. The pots will absorb the water.
- Place the pots on a sunny sill, under grow lights, or in a greenhouse. Watch for sprouts within two weeks.
- Transplant the peat pots directly in the ground in the spring. The pots break down over time without disrupting the milkweed's roots.
Common Pests & Plant Diseases
The usual suspects are attracted to common milkweed, including milkweed bugs (which don't do too much harm, in fact), aphids, whiteflies, scale insects, spider mites, thrips, and leaf miners. Use a hose, spray from a bottle, or fingernails to scrape off the offenders. Snails and slugs also love young tender milkweed plants. Snail bait works well and won't harm monarchs, but as the plants grow, the snail problem minimizes.
Is common milkweed good to plant in a border garden?
Common milkweed spreads fairly aggressively, and some gardeners and local agencies advise to be careful where you plant it for this reason. It is too weedy and aggressive for most mixed border gardens unless you are specifically creating a butterfly garden. You can try containing the plant by putting it in the back of your garden where it has limited space to spread.
What type of pesticides should I use on common milkweed?
It is important not to use pesticides in a butterfly garden, as the same chemicals that kill destructive insects will also kill butterflies and their larva. Most gardeners find, though, that once a garden goes chemical-free, it establishes a good balance of beneficial, predatory insects, and provides songbirds with a source of food (many bird species consume large quantities of insects).
How do I plant common milkweed to attract butterflies?
If you are planting common milkweed to encourage monarch butterflies, create a small patch of milkweed that includes at least six plants. Include a nearby water source for your butterflies; a birdbath or a large potting saucer filled with water will work fine. Planting other pollinator-friendly plants in a comprehensive butterfly garden is a good idea.
Milkweed can Cause Serious Poisoning. National Capital Poison Control.
“5 Steps to Planting Milkweed Seeds Indoors.” Save Our Monarchs, https://www.saveourmonarchs.org/blog/5-steps-to-planting-milkweed-seeds?gclid=Cj0KCQiAoNWOBhCwARIsAAiHnEgGtjagcWTAaT_mMN2rh_I9jegbyCfswodF0IU9JABUI2TR_9YPNUkaAq69EALw_wcB. Accessed 5 Jan. 2022.
“Yard and Garden: All about Milkweed.” News, https://www.extension.iastate.edu/news/yard-and-garden-all-about-milkweed
James, David G. A Neonicotinoid Insecticide at a Rate Found in Nectar Reduces Longevity but Not Oogenesis in Monarch Butterflies, Danaus plexippus (L.). (Lepidoptera: Nymphalidae). Insects, 10(9): 276, 2019. doi:10.3390/insects10090276