Different types of milkweed

Want to attract more monarch butterflies to your garden? Boost their numbers with these milkweed types and tips.

Common Milkweed (Asclepias syriaca) credit: AnRo0002

Last year I moved to an area dotted with well-manicured lawns. One of the first things I did? Replace some of my own monoculture turf with several native milkweed plants. It didn’t take long for my neighbors to notice all the monarch butterflies I’d attracted. Was it magic? Sort of!

Although monarchs and milkweed go hand-in-hand, not everyone understands their special connection. Milkweed contains toxins called cardenolides. Monarch butterflies lay their eggs on milkweed, the eggs hatch into caterpillars, and these caterpillars feed exclusively on milkweed. Storing up cardenolides as they go, the caterpillars — and the adult monarchs they will become — remain unaffected, but birds and other predators become ill after ingesting the substance. The monarch’s bright colors further protect it by signaling this toxicity.

Picking Your Poison

Adding milkweed to your landscape is simple enough, but some types serve monarchs in your zip code better than others. Ideally, you should choose some native species and some that can work as perennials in your climate zone. (Check the USDA Plant Hardiness Zone Map as needed.)

Living in the western U.S.? You can enter your state into this Monarch Milkweed Mapper to see which species will perform best for you. Also, the Xerces Society for Invertebrate Conservation includes several region-specific milkweed guides for people in the East, Southeast, and elsewhere.

Photo by Susan Brackney

Skip the Tropics

Although tropical milkweed (Asclepias curassavica) is popular and easy to grow, it isn’t ideal — especially if you’re in the south or southwestern U.S. Because tropical milkweed can live year-round in warm climates, monarchs may miss important environmental cues which normally trigger winter migration. Furthermore, without regular pruning, tropical milkweed can harbor and spread disease. Add climate change’s warmer temperatures to the mix, and the case against tropical milkweed becomes even stronger, according to a 2018 study in Ecology.

After growing tropical and swamp milkweed in both ambient and very high temperatures, the researchers suggested, “ represents a potential ecological trap for monarchs.” When grown in the hotter environment, tropical milkweed produced very high cardenolide levels which, along with the high temperatures, negatively affected monarchs.

Photo by Susan Brackney

Common, Showy, and Swamp

Not sure just where to start? Native to much of the eastern and central U.S. and Canada, common milkweed (Asclepias syriaca) features large, leathery leaves and globelike, pinkish blooms. And, with breathtaking starlike flowers, the aptly named showy milkweed (Asclepias speciosa) thrives throughout the central and western U.S. and Canada. For its part, swamp milkweed (Asclepias incarnata) tolerates clay-heavy soils, likes “wet feet,” and ranges widely throughout the U.S. and eastern Canada. Compared to its common and showy counterparts, swamp milkweed’s leaves are narrower and its flower clusters are more delicate and compact.

Once you settle on your milkweed types, you may be able to find them via a local or regional nursery. Try the Xerces Society’s Milkweed Seed Finder to see what’s nearby. Before you buy? Make sure the vendor’s seeds and plants are pesticide-free.

Milkweed Plant Varieties – Growing Different Milkweed Plants

Because of agricultural herbicides and other human interference with nature, milkweed plants are not as widely available for monarchs these days. Continue reading to learn more about different types of milkweed you can grow to help future generations of monarch butterflies.

Different Types of Milkweed

With monarch butterfly populations having dropped more than 90% in the last twenty years because of a loss of host plants, growing different milkweed plants is very important for future of monarchs. Milkweed plants are the monarch butterfly’s only host plant. In midsummer, female monarch butterflies visit milkweed to drink its nectar and lay eggs. When these eggs hatch into tiny monarch caterpillars, they immediately begin to feed on the leaves of their milkweed host. After a couple weeks of feeding, a monarch caterpillar will seek out a safe place to form its chrysalis, where it will become a butterfly.

With over 100 native species of milkweed plants in the United States, almost anyone can grow varieties of milkweed in their area. Many types of milkweed are specific to certain regions of the country.

  • The Northeast Region, which runs down through the center of North Dakota through Kansas, then east through Virginia and includes all states north of this.
  • The Southeastern Region runs from Arkansas through North Carolina, including all states south of this through Florida.
  • The South Central Region includes only Texas and Oklahoma.
  • The Western Region includes all western states except for California and Arizona, which are both considered individual regions.

Milkweed Plant Varieties for Butterflies

Below is a list of different types of milkweed and their native regions. This list does not contain all varieties of milkweed, just the best kinds of milkweed to support monarchs in your region.

Northeast Region

Southeastern Region

South Central Region

  • Antelopehorn milkweed (A. asperula)
  • Green Antelopehorn milkweed (A. viridis)
  • Zizotes milkweed (A. oenotheroides)

Western Region

  • Mexican Whorled milkweed (A. fascicularis)
  • Showy milkweed (A. speciosa)

Arizona

  • Butterfly weed (A. tuberosa)
  • Arizona milkweed (A. angustifolia)
  • Rush milkweed (A. subulata)
  • Antelopehorn milkweed (A. asperula)

California

The Effects of Different Species of Milkweed on Monarch Development

Janelle Firl, Julia Goldberg, and others
Willow Creek Middle School and Century High School
Rochester, MN

Julia and Janelle with their insect fair project display (Photo: Janelle Firl and Julia Goldberg)

Abstract

We wanted to find out how different species of milkweed affected developing monarchs. We raised 100 monarch butterflies from eggs: 20 on swamp milkweed, 20 on common milkweed, 20 on whorled milkweed, 20 on tropical milkweed, and 20 on butterfly weed. All conditions other than food were controlled (held constant). Larvae fed on tropical milkweed had the highest survival rate and the shortest time to pupation. Larvae fed whorled milkweed and butterfly weed had the lowest survival rate and the longest time to reach pupation. Common and swamp milkweed were in the middle. We are uncertain about the causes of the high mortality in our experiment. We learned that diet is an important factor in larval development. We also learned that doing an experiment like this is a lot of fun…but also work!

Introduction

We thought that different species of milkweed might have different nutritional and physical characteristics that could affect the survival rate, rate of life cycle, mass, and fitness of monarchs. We had observed that different species of milkweed had different textures, thicknesses, sizes, and shapes, as well as different pubescences. We had also done some research and discovered that different species of milkweed have varying amounts of toxin. Just like how different kinds of lettuce have different nutritional values, we thought different milkweed species would also have different nutritional values. Therefore, consumption of a particular milkweed might lead to contrasting levels of fitness.

Hypotheses

  • Null: There will be no connection between survival to pupation and different milkweed species.
  • Actual 1: Monarchs reared on different milkweed species will have different rates of survival.
  • Actual 2: Since common milkweed is most prevalent, monarchs will survive to pupation best when reared on common milkweed.

Experimental Design

  • For each treatment we obtained a random block of 20 eggs, using 2 eggs from 10 different females. All eggs were laid within a 3-hour period.
  • The eggs were distributed into 5 identical containers.
    • Eggs were kept on damp paper towel.
    • Milkweed was picked every 2 days and stored in the refrigerator. Sprigs of 5 different types of milkweed were inserted into floral tubes:
      1. Tropical – Asclepias curassavica
      2. Swamp – Asclepias incarnata
      3. Butterfly weed – Asclepias tuberosa
      4. Common – Asclepias syriaca
      5. Whorled – Asclepias verticillata
    • Milkweed was changed daily.
    • Larvae were maintained in containers until adulthood.
  • All other variables (temperature, light, etc) were kept constant (controlled).
  • An inventory was made of instar stages and date of pupation of all larvae in each container and recorded in a data book.
  • Upon emergence, the butterflies were separated by gender and then tagged with stickers indicating their milkweed treatment.
  • On the second day of adulthood, they were weighed and tested for parasites.

Summary

Our experiment went relatively well, with few problems. The problems we experienced were that with the overwhelming speed at which the monarchs emerged from the pupae stage, we were unable to record longevity. Another problem we experienced was the problem of having 20 original eggs in a container, but being unsure of the percentage of fertilization. This meant that when we recorded our numbers and percentages, they were out of 20 original eggs, and not the number of eggs that have hatched. We also had a problem after we labeled the adult monarchs with stickers, for some of them came off. This caused us to be unable to record the date of death for many of the butterflies.

Results

Larvae fed on tropical milkweed had the highest survival rate and the shortest time to pupation. Larvae fed whorled milkweed and butterfly weed had the lowest survival rate and the longest time to reach pupation. Common and swamp milkweed were in the middle.

(Photo: Janelle Firl, Julia Goldberg, and others)

Conclusion

The conclusion was that eating different species of milkweed does affect survival rate, adult mass, and the rate of the life cycle. The results show that monarchs fed tropical milkweed had the highest survival rate, shortest time to pupation, and the heaviest adults. Larvae fed butterfly weed had the lowest survival rate, longest time to pupation, and the lightest adults. For the other species of milkweed there was not as noticeable of a difference. Although common milkweed performed well, it was second to tropical in survival to pupae and average number of days to emergence. It was third behind tropical and whorled in average weights of adults.

Next Time

We are uncertain about the causes of the high mortality in our experiment. We learned that diet is an important factor in larval development. If we were ever to do another experiment of this kind, the only things we would change would be writing identification numbers directly on the wing of the adult monarchs and we would arrange for more people to record information on the monarchs everyday.

7 milkweed varieties and where to find them

Milkweeds are not the most spectacular of flowering perennials, but they can look highly effective as fillers and textural foils in plant combinations. They are a must in any sunny herbaceous garden where the gardener wants to attract monarch butterflies.

Three or so species are typically found in home gardens, but others deserve to be grown as well. As a group, they have two things against them: They can be hard to find and there’s that word “weed” in their name.

They are wild plants, growing on disturbed land, and some species will spread if unchecked, but their “weed” label is for the most part a throwback to an age when native flora was undervalued and naturalistic gardens were generally unknown.

Some milkweeds will probably never be valued garden plants, but it is interesting that a dozen species are known to grow in the Mid-Atlantic.

Asclepias verticillata. (James Gagliardi/Smithsonian Gardens)

Here are ones of particular value to gardeners who want to support monarchs and other pollinators:

1. Butterfly milkweed (Asclepias tuberosa): This is grown for its clusters of orange flowers, which appear in late spring and early summer. They develop into showy seed pods that break open to reveal seeds with silken hairs. It grows three feet high and two feet across and prefers sun to partial shade. Avoid planting them in heavy wet soil.

2. Swamp milkweed (Asclepias incarnata ): This will take wet soil, as its name suggests, though it doesn’t need it to flourish. Plants bloom later than butterfly milkweed, and the flowers are a pale to deep rose pink. A variety named Ice Ballet has creamy white flowers. The plant will grow to four feet tall and two feet across.

3. Whorled milkweed (Asclepias verticillata ): This variety has fine leaves and small, white flower clusters that appear in early summer. It’s resistant to deer browsing but also toxic to livestock. It grows to three feet high by two feet across.

4. Common milkweed (Asclepias syriaca ): This is the coarsest of milkweeds and the one most considered a genuine weed by farmers for its ability to form invasive clumps by underground runners. This same quality makes it great for holding soil banks together. Colonies grow to six feet tall and just keep spreading. The flowers appear in June as dull purple balls.

5. Purple milkweed (Asclepias purpurascens ): This deserves more use but is hard to find because of poor seed germination rates. It forms handsome, spreading clumps five feet tall, but by late season it suffers from weevil damage.●

6. Balloon plant (Asclepias or Gomphocarpus physocarpus ): This is a tropical, non-native annual milkweed grown as a garden curiosity, though monarchs feed on it. It is grown for its size — six feet tall by late summer — and its lime green, spiky seed pods.

7. Tropical milkweed (Asclepias curassavica ): Tropical milkweed, sometimes called blood flower, is not a native milkweed, nor is it hardy in the Mid-Atlantic. It may self-seed here. It grows to three feet tall and two feet across, with bright red-orange flower clusters. It is attractive, but has its ecological detractors.

Where to find milkweed

Obtaining milkweed for the garden can be challenging. Even if you have a friend with milkweed to spare (don’t collect from the wild), established plants are deep-rooted and won’t move well.

Seed may be stubborn to germinate and may need a period of cold treatment.

Another consideration: Plants at garden centers may have been treated with pesticides that could harm feeding caterpillars. Plants that have been sprayed with contact insecticides will produce fresh, untreated growth, but plants raised with systemic pesticides such as neonicotinoids will remain toxic to monarch larvae. Ask what pesticides have been used in growing the plants.

These specialty nurseries and native plant groups sell milkweed plants, typically the swamp milkweed, common milkweed and butterfly milkweed. Check hours and plant availability before setting out.

→Nature by Design

300 Calvert St., Alexandria. 703-683-4769. www.nature-by-design.com.

→Hill House Farm and Nursery

631 Scrabble Rd., Castleton, Va. 540-937-1798. www.hillhousenativeplants.com.

→Earth Sangha

Franconia Park, entrance at the end of Cloud Drive, Springfield. 703-764-4830. www.earthsangha.org.

→Watermark Woods Native Plants

16764 Hamilton Station Rd., Hamilton, Va. 540-441-7443. www.watermarkwoods.com.

→Abernethy and Spencer

18035 Lincoln Rd., Lincoln, Va. 540-338-9118. www.abernethyspencer.com.

→Loudoun Wildlife Conservancy

The conservancy is holding a milkweed plant sale Sunday at 12:30 p.m. at Morvern Park, 17263 Southern Planter Lane, Leesburg. 703-777-2575. www.loudounwildlife.org.

→Chesapeake Natives

The nonprofit nursery will hold a sale (nectar plants and some common and butterfly milkweeds) Sunday 10 a.m. to 2 p.m. at Rosaryville State Park, 9640 Rosaryville Rd., Upper Marlboro. 202-262-9773. www.chesapeakenatives.org.

→Monarch Watch

The organization sells 32-plug flats of milkweed, maybe too many for one garden but enough to share with others. 888-824-4464. www.monarch
watch.org/milkweed/market.

→Herring Run Nursery

Plant sales are staged in the maintenance area of the Mount Pleasant Golf Course in north Baltimore, 6131 Hillen Rd., Baltimore. This weekend and next, 10 a.m. to 3 p.m. Four species available. 410-254-1577. www.bluewaterbaltimore.org/herring-run-nursery.

— Adrian Higgins

Plant of the Week

Range map of Asclepias syriaca. States are colored green where the species may be found.

Whole plant with flowers. Photo by David Taylor.

Asclepias syriaca pods. Photo by David Taylor.

Monarch caterpillar on leaf. Photo by David Taylor.

Large milkweed bug adults and nymphs. Photo by David Taylor.

Tussock moth caterpillars. Photo by David Taylor.

Predated seeds. Photo by David Taylor.

Common Milkweed (Asclepias syriaca L.)

By David Taylor

Common milkweed is a member of the Asclepiadaceae (milkweed) family. It is one of about 115 species that occur in the Americas. Most species are tropical or arid land species. The genus name, Asclepias, commemorates Asklepios, the Greek god of medicine. Some of the milkweed species have a history of medicinal use including common milkweed (wart removal and lung diseases), and butterfly weed, A. tuberosa (also known as pleurisy root, used for pleurisy and other lung disease). The specific epithet, syriaca, means ‘of Syria’ in reference to Linnaeus’s mistaken belief it was from Syria. It is a widespread and somewhat weedy species known from most of the eastern United States and the eastern most prairie states as well as southern Canada from New Brunswick to Saskatchewan. It is frequently found in fence rows, on roadsides, in fields, and in prairies and pastures. Given the opportunity, it will establish in gardens and even thin lawns. It is tolerant of light shade, but generally is a full sun species.

This milkweed grows to about 1.5 meters(5 feet) tall, usually occurring in clusters of stout stems. It has rhizomes and quickly forms colonies. Leaves are 15-20 centimeters (6-8 inches) long and 5-9 centimeters (2-3.6 inches) wide. They are somewhat thick with a prominent midrib beneath. The upper surface is light to dark green while the lower surface is lighter, almost white at times. Broken leaves and stems exude a milky latex. Flowers are borne in nearly spherical clusters (umbels) at the top of the plant, usually with 2-5 clusters per plant. Each flower is about 2 centimeters (0.75 inches) long and 1 centimeters (0.4 inches) wide. Flowers are greenish-pink to rosy pink to purplish-pink and very strongly and sweetly scented. Fruits (pods) are about 10 centimeters (4 inches) long, inflated and covered in little finger-like projections. They are green initially, turning brown as they mature. They split open revealing 50-100 seeds each with a white, fluffy coma (“parachute”) that allows wind dispersal.

Common milkweed is Nature’s mega food market for insects. Over 450 insects are known to feed on some portion of the plant. Numerous insects are attracted to the nectar-laden flowers and it is not at all uncommon to see flies, beetles, ants, bees, wasps, and butterflies on the flowers at the same time. Occasionally hummingbirds will try, unsuccessfully, to extract nectar. Its sap, leaves and flowers also provide food. In the northeast and midwest, it is among the most important food plants for monarch caterpillars (Danaus plexippus). Other common feeders are the colorful (red with black dots) red milkweed beetle (Tetraopes tetraophthalmus), the milkweed tussock caterpillar (Euchaetes egle) and the large (Oncopeltus fasciatus) and the small (Lygaeus kalmia) red and black milkweed bugs. The latter two are particularly destructive as both the adults and nymphs are seed predators. They can destroy 80 to 90 percent of a colony’s seed crop. The red (or orange-red) and black coloration of most of these insects is known as aposematic coloration; that is, the colors advertise the fact that the organism is not good to eat.

Milkweeds contain various levels of cardiac glycoside compounds which render the plants toxic to most insects and animals. For some insects, the cardiac glycosides become a defense. They can store them in their tissue which renders them inedible or toxic to other animals. Monarch butterflies use this defense and birds leave them and the caterpillars alone. What the birds do not know is that northern monarchs feeding on common milkweed accumulate relatively little of the toxic compounds and probably would be edible. The more southern butterflies accumulate large amounts of the compounds from other milkweed species and are in fact toxic. Monarchs can be helped by encouraging existing patches and planting new ones. The plant grows readily from seed and spreads quickly by deep rhizomes. Because common milkweed can be weedy and difficult to remove, care should be used to establish the plant only in places where spread can be tolerated.

For More Information

  • PLANTS Profile – Asclepias syriaca, common milkweed
  • See other Plant of the Week Asclepias species…
  • Monarch Butterfly: Habitat Needs

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