Asclepias — Or How I Learned to Love Milkweed

• By Pat Chadwick
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• June 2016-Vol.2 No.6
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• 5 Comments

While I have strong feelings, pro or con, about most plants, I feel ambivalent about a few.  Asclepias (pronounced ah SKLEE pee us) is one of those, but my attitude toward it has gradually evolved.  As a child growing up on a farm, I knew this plant by its common name — milkweed.  A large, coarse-looking weed, it had little to offer in the way of charm.   It grew aggressively throughout several of the farm’s pasture fields, but the cows and horses avoided it.  I learned early on that if you break the leaves or stems of this plant, a sticky, white sap oozes out and irritates your skin.  The cows and horses, clearly smarter than I was, knew that and left these plants alone.  Once the plant bloomed and set seed, my attitude toward it mellowed a bit.  On the one hand, the spherical clusters of oddly shaped small flowers were interesting to examine.  On the other hand, the flowers were a dull and decidedly unappealing shade of anemic pink.  The monarch butterflies flitting around this plant didn’t seem to mind the color, though.  I guessed, perhaps accurately, that they were attracted to the pleasant scent of the flowers.

In my childlike mind, the only reason milkweed needed to exist was because of its seedpods.  When they matured, they split open, revealing perfectly aligned rows of brown seeds with long, fluffy white hairs attached to them.  As a bored kid with an insatiable curiosity about nature, those seedpods provided me with endless hours of amusement.

Fast forward to adulthood, when I eventually learned about the relationship between milkweed and the life cycle of the monarch butterfly. What an epiphany to discover that the same homely weed about which I felt ambivalent as a child is critical to this beautiful creature’s very existence, specifically at the larval stage.  Looking at milkweed in a whole new light, I set out to learn more about it.  I discovered, for example, that:

• It is named after the Greek god of medicine, Asklepios.  I can only surmise that this must be a pretty important plant to be given such an auspicious name.
• Legend has it that this plant has been used throughout history to treat a variety of medical conditions, including pleurisy, arthritis, gall stones, stomach ailments, and even warts.
• The sticky white sap is mildly poisonous and its bitter taste warns away most animals and insects that attempt to eat it.  Monarch butterfly larvae seem not to be bothered by either the bitter taste or the toxin.  In fact, by feeding on the leaves, they accumulate enough of the toxin in their bodies to make themselves distasteful to predators.
• During World War II, the buoyant milkweed floss was used as a substitute for kapok in life jackets.

With my new-found knowledge about milkweed, I eventually decided it was time to adjust my attitude about it.   With some (OK, a lot of) reluctance, I added a couple of species to my ornamental garden a few years ago.  I dreaded the idea of incorporating bright orange or other “hot” colors in my garden, which consists predominately of “cool” colors.  Also, there’s something counterintuitive about installing an ornamental plant that is meant to be eaten.   But, you know what? Despite my apprehension, this species has finally grown on me.  Perhaps it took a few monarch butterflies to help me see the light.  Ambivalent no longer, I now find myself hovering anxiously over it in the spring time, waiting for it to break dormancy.  As for the seedpods, I haven’t quite outgrown the desire to play with them, but I’m working on it.

Whether you call it Asclepias or milkweed, the genus consists of more than 100 species of evergreen or deciduous, clump-forming or spreading perennials.  Flora of Virginia lists 15 members of the genus that are native to this state. Of those 15 species, A. tuberosa and A. incarnata tend to be the most commonly grown in the ornamental garden.   Those and a few other selected species are described below.

• A. syriaca (Common Milkweed).  This is the species that flourished with wild abandon on the farm where I grew up.   It is commonly found throughout much of the eastern United States, particularly along roadsides and in meadows and pastures.  It typically grows about 4 to 5 feet tall and, as mentioned earlier, sports clusters of dull, some might say unappealing, pale pink flowers from late June through July.
  

  Asclepias syriaca

  What this plant lacks in color, it makes up for with a distinctive musky scent that butterflies adore. This is not a particularly attractive plant, which is why it’s not ordinarily found growing in orderly, cultivated gardens.  Also, it can aggressively spread by underground rhizomes.

• A. tuberosa (Butterfly Weed).  This smaller, more refined species grows from 1-1/2 to 3 feet tall and has narrow leaves and clusters of bright orange flowers.  If you’ve ever seen this one growing in the wild, the color fairly jumps out at you (in an attractive way).   Of all the native species, this one appears to be the easiest to find in garden centers and plant catalogs.  A couple of cultivars are available in addition to the orange species:
  • ‘Gay Butterflies’ – This 2 to 3-foot tall plant bears red, orange or yellow flowers.
  • ‘Hello Yellow’
    

    Asclepias tuberosa ‘Hello Yellow’

    — This 2 to 2-1/2 foot tall plant bears bright yellow flowers.  I planted this cultivar a couple of years ago but found the yellow color just a little too vibrant for my tastes.  So I moved it to another spot in the garden where it will blend in better with its neighbors.

• A. incarnata (Swamp Milkweed).  This thick-stemmed species grows about 3 to 4 feet tall.  The clusters of pink flowers are more colorful than those of its A. syriaca cousin. The flowers have a mild vanilla scent that butterflies go wild over.  This species grows in ditches, swamps, and other moisture-retaining soil.A. incarnata cultivars include:
  • ‘Ice Ballet’ – Slightly smaller than the species at 32 to 40 in. in height, it bears white flowers.
  • ‘Cinderella’ — Growing to about 3 feet tall, it has soft pink flowers that open from deep pink buds. This cultivar can tolerate a dry site.
  • ‘Soulmate— Growing to about 3 feet tall, it has rosy-purple flowers. Like ‘Cinderella’, this cultivar can also tolerate a dry site.
    

    Asclepias incarnate (Swamp Milkweed)

• A. purpurascens (Purple Milkweed).
  

  Asclepias purpurascens (Purple Milkweed)

  This 2 to 3-foot tall species gets its name from the reddish-purple rib on the leaves.  Unfortunately, it is not as commonly available as A. tuberosa or A. incarnata.  As reported by Allan Armitage in his Herbaceous Perennial Plants, this is one of the most attractive members of the genus.  The thick clusters of fragrant flowers start out as dusky pink buds and open to an eye-catching deep rose to reddish-purple color. Although similar in form to its relative A. syriaca, this species is a gentle spreader in the garden.

• A. variegata (White Milkweed).
  

  Asclepias variagata (White Milkweed)

  This species grows from 1 to 4 feet tall with densely arranged clusters of white blossoms having a faint touch of purple at the base of each individual flower.

• A. verticillata (Whorled Milkweed). This 1 to 3-foot tall species has narrow, whorled leaves and small creamy white flowers along the length of the stems.  One of the most widely distributed of all Asclepias species in the U.S., this selection is one of the few clone-forming species.   Although unlikely to be found in cultivated or grazed landscapes, it does colonize in ditches and along roadsides and is a common late season host plant for monarch larvae.
  

  Asclepias verticillata

In addition to the native species, the following tropical non-natives also support monarch butterfly populations.  Although technically perennials, they are not hardy in Zone 7 and must be grown as annuals.

• A. Curassavica (Blood Flower or Tropical Milkweed) – This South American native is hardy only to Zone 9.  It grows between 2 and 3 feet tall and produces clusters of yellow and red bi-colored flowers during the latter half of summer into fall.  It will self-sow in most gardens but resents being transplanted.  Readily available through garden centers and on-line sources, it is a favorite nectar source for a wide variety of butterflies, including monarchs.  In the interest of full disclosure, my research revealed some concern about this plant in the southern-most U.S. (Florida and Texas).  Because it stays alive in those warmer climates, the concern is that the monarchs may stick around to feed on it rather than migrate to their usual wintering grounds.  This should not be a problem in Virginia because this plant is not hardy here.  However, if you do grow it and have any concerns about it, cut it back in the fall before it self-sows.

Asclepias curassavica

• Gomphocarpus physocarpus (Balloon Flower) – Once in a while, I encounter a plant that causes me to stop dead in my tracks in wonder.
  

  Gomphocarpus physocarpus (formerly Asclepias physocarpa)

  Such a plant caught my attention at the Green Springs Botanical Garden in northern Virginia about 10 years ago.  The white blossoms on this large, 5-foot tall plant clearly resembled those belonging to members of the Asclepiadaceae genus.  However, it definitely did not resemble any Asclepias species with which I was familiar.   What had me baffled was the pale green, softly spiny-looking clusters of 2 to 2-1/2 inch round, balloon-like seed pods.   Although unusual in appearance, the seedpods were oddly attractive.  Upon researching this plant with its unpronounceable botanical name, I learned that it had been formerly classed as A. physocarpa — a member of the Asclepias family.  It was apparently renamed to indicate its southeast Africa origin.  I never forgot that plant and was delighted to encounter another specimen two years ago in the butterfly garden at the Biltmore estate in North Carolina.   Mature monarch butterflies as well as larvae and pupae liberally covered the plant.  To say that my fellow visitors and I were thoroughly enchanted by both the plant and the cloud of monarchs flitting about it is an understatement!

HOW TO USE ASCLEPIAS IN THE LANDSCAPE

To provide a source of nectar for adult monarchs and leaves for the larvae, try planting several species of Asclepias, preferably ones that are native to this area.   Don’t limit yourself to just one or two plants.  Plant as many as you can reasonably fit into your garden.

• Butterfly garden – Incorporate with other nectar-rich plants to attract butterflies and other pollinators.  A few companion plants that come to mind include Joe Pye weed (Eupatorium maculatum), cardinal flower (Lobelia cardinalis), great blue lobelia (Lobelia siphilitica), coneflower (Echinacea), Mexican sunflower (Tithonia rotundifolia), bergamot (Monarda), goldenrod (Solidago), ironweed (Vernonia), and various asters.
• Meadow or wildflower gardens — This is a particularly suitable application for the larger, coarse-leaved varieties, such as A. syriaca.  Be sure to include other species that bloom later in the season in order to provide a source of food throughout the growing season.
• Mixed border – Include in a mixed perennial and annual border.  Some varieties, as already noted, have strong colors.  They work best in a border with other “hot” colors, including such plants as tickseed (Coreopsis), black-eyed Susan (Rudbeckia), yarrow (Achillea) and blazing star (Liatris).
• Decorations – The seedpods can be used in very interesting ways in dried arrangements.  The inner shell of A. syriaca, for example, has a faint silvery sheen that looks particularly attractive when combined with other dried plant materials in holiday wreaths.

CARE AND MAINTENANCE

Plant Asclepias in average to poor soil that drains very well.  Sandy soil is ideal. Swamp milkweed can tolerate moist soil, as its name suggests, but also grows well in dry soil.  Asclepias prefers full sun but will tolerate partial shade.  Rich soil or heavy shade can cause the stems to be weak or floppy.

Asclepias are among the last of the perennials to emerge in spring.  You might be wise to mark where you plant them or leave the stalks in place over winter so that you don’t lose track of them the following spring.

Handle with care.  The foliage contains latex, a milky substance that may irritate your skin.  If ingested, the plant can be poisonous to both animals and humans.

PROPAGATION

Asclepias may be propagated by seed, stem cuttings, or root cuttings. For best results with seeds, sow them directly into a bed in autumn or early winter.  The seed of most species needs to be stratified (subjected to a period of cold temperatures) before they sprout in the spring.   Alternatively, seeds may be sown in spring but, to improve the germination rate, stratify them first.  The easiest way to do this is to place them between moist paper towels in a plastic bag and refrigerate them for about 3 to 6 weeks.  Then, remove the seeds from the refrigerator and soak them in warm water for about 24 hours before planting them.  The warm water bath further improves the germination rate.  Tropical species of Asclepias do not require stratification in order to germinate.

To propagate by stem cutting, sever a 3 to 4-inch cutting from a green stem that is about 1/3^rd inch thick.  Make the cut ¼ inch below a leaf node.  Remove the lower leaves, dip the cut end of the stem into a rooting compound, and insert the cutting into a container that is filled with moist sand, vermiculite or potting soil. Cover the container with plastic wrap or a glass jar to maintain high humidity until the plant starts to develop roots.  Mist the soil as needed to keep it moist but not soggy.  Cuttings generally require about 6 to 10 weeks to develop good root systems before they can be planted in the garden.

Root cuttings are the trickiest method of propagation for this plant and not generally recommended.  Asclepias has an extensive root system, and if the long tap root is damaged, it may not recover.  If you do attempt this method of propagation, carefully sever a portion of the root system when the plant is dormant.  To root the cutting successfully, make sure it has one or more shoot buds.

PESTS AND DISEASES

Anyone who has ever grown Asclepias knows that it attracts aphids.  These pests, usually orange or yellow in color, cover the stems and leaves of the plant and sap it of its juices.  Ridding the plant of aphids is tricky business because of the risk of harm to monarch butterfly eggs, larvae and pupae.   Here are several strategies for combating these pests:

• Inspect Asclepias stems and leaves (both sides) daily.  Take immediate action at the first aphid sighting.  Don’t procrastinate.  The sooner you take action, the less of a problem you’ll have over the growing season.
• Squish the aphids with your fingers, preferably gloved, of course.  Try not to damage the foliage and stems in the process.  A small brush sometimes works well in dislodging aphids, especially from the little nooks and crannies and other tight spots.
• Carefully direct a spray of water at the aphids to dislodge them.  As you do this, be extremely careful not to spray monarch eggs or larvae. Otherwise, you’ll dislodge them, too.
• Let natural predators take care of the job.  Lady beetles, lacewings, parasitic wasps, and mantids are natural enemies of aphids.  However, they also eat monarch eggs.
• For further information on aphids and controls, see VCE Publication 444-220, “Aphids.”  Keep in mind one important fact:  Any controls used for aphids, regardless of how benign, may also affect monarch eggs or larvae.  Proceed carefully with any pest treatment you use.

Milkweed bugs (Oncopeltus fasciatus) are another common pest of the plant.  Unlike aphids, which do a lot of harm, milkweed bugs are more of a nuisance than an actual threat to the plant.  These colorful orange and black insects are usually found in small groups feeding on the seeds, stems and leaves.  The adult insect lives only about a month and doesn’t do much harm to the plant.   The Missouri Botanical Garden website advises simply living with the damage.  Removing leaf litter and spent plant material in the fall helps to control these insects.

Several foliar or fungal diseases, such as powdery mildew, leaf spots and rusts, may affect Asclepias.

• Powdery mildew may develop on the leaves when there’s a mixture of both damp and dry conditions caused by foggy mornings followed by very dry weather later in the day.  There’s generally not much that can be done or that needs to be done for this problem.
• Leaf spots are caused by irregular watering or by lack of good air circulation. This is a concern because the diseased leaves are not suitable for monarchs to feed on.  To prevent the problem, avoid overhead watering, especially in the evenings when foliage cannot dry off properly.  Proper spacing of plants is essential for promoting good air circulation.  Remove any affected leaves, particularly those that fall to the ground.
• Rust stunts the growth of foliage and causes reddish-color spots on leaves.  Carefully remove affected leaves to avoid scattering the fungal spores.

SOURCES

A-Z Encyclopedia of Garden Plants (American Horticulture Society, 2008)

“Aphids,” Va. Coop. Ext. (pubs.ext.vt.edu/444-220)

Herbaceous Perennial Plants, Third Edition, (Armitage, Allan M., 2008)

Lady Bird Johnson Wild Flower Center, The University of Texas at Austin, (www.wildflower.org/plants)

“Milkweed Bugs,” Missouri Botanical Garden website (Milkweed Bugs)

Monarch Watch (educational outreach program based at University of Kansas, (monarchwatch.org)

“Monarchs and Milkweeds,” National Wildlife Federation website (Pollinators/Monarchs)

Piedmont Virginia Native Plant Database (www.albemarle.org/NativePlants/list)

“12 Native Milkweeds for Monarchs,” National Wildlife Federation website (12 Native Milkweeds for Monarchs)

United States Department of Agriculture Plant Database (plants.usda.gov)

Virginia Department of Conservation and Recreation, (dcr.virginia.gov/natural-heritage/nativeplants)