Mother Nature's Montrose Garden: July 2019

Showy milkweed (Asclepias speciosa): Mother Nature's Montrose Garden,

Montrose, Colorado

Summer blooming plants really come into their own in July, growing and flowering like crazy with the long, warm days. One of the prettiest in Mother Nature’s Montrose Garden is the Showy milkweed, Asclepias speciosa. The name speciosa means ‘showy’, which certainly describes this native perennial. The scientific name is pronounced: ass-KLE-pee-us spee-see-OH-suh.

Showy milkweed is a true native milkweed, of the genus Asclepias, in the subfamily Asclepiadoideae of the Dogbane family (Apocynaceae). There are over 200 species of milkweed worldwide and 19 are native to Colorado. The Milkweeds are named for the milky ‘sap’ released when plants are damaged. This sap contains toxic and medicinal chemicals (more on this later). The genus was named by Linnaeus to honor Asclepias, the ancient Greek demi-god of medicine.

As with most native plants, the Colorado Milkweeds of the Western Slope are somewhat different from those of the Front Range and Eastern Colorado. Showy Milkweed is found on both sides of the Rockies, and is a good garden choice throughout Colorado. The natives to Western CO (in addition to Asclepias speciosa) are: Asclepias asperula (Antelope-horn or Creeping Milkweed), Asclepias cryptoceras (Pallid or Adobe Milkweed), Asclepias cutleri (Cutler's Milkweed), Asclepias hallii (Hall’s Milkweed), Asclepias involucrata (Dwarf Milkweed), Asclepias macrosperma (Big Seed Milkweed, Eastwood's Milkweed), Asclepias subverticillata (Whorled Milkweed), and Asclepias tuberosa (Butterfly Milkweed).

Monarch butterfly larva

Most people know that Milkweeds are important food plants for Monarch butterflies. The Monarch caterpillars (larvae) eat the milkweed leaves and stems, ingesting the plant chemicals. The chemicals are not toxic to the caterpillars, but they do make Monarch caterpillars unpalatable or toxic to their predators (mostly birds and insects). Many gardeners grow Milkweeds specifically for their Monarch habitat value. We don’t have large numbers of Monarchs in Colorado, but they are seen occasionally. And there is much current interest in the Monarchs of the Southwestern U.S. For more good resources on Monarchs, see references 1-4, below.

Monarch butterfly

Showy milkweed (Asclepias speciosa): along
irrigation ditch, Montrose County, CO

Showy Milkweed is a common plant in the west. It can be found growing wild from Minnesota to British Columbia, Canada, in the north, and south to Texas, the Four Corners states and California. It grows in many plant communities, in sandy to loamy soils, up to about 6500 ft. (1900 m.) elevation. It favors places that get a little extra water: around lakes, streams and drainage channels, along roadsides and in other semi-moist places. In Western Colorado, it’s often seen on the banks of irrigation channels and streams. It’s common enough that it can appear naturally in home gardens – as it did in Mother Nature’s Montrose Garden.

Showy milkweed (Asclepias speciosa):
reseeded plants

Showy milkweed (Asclepias speciosa):
growth habit

Asclepias speciosa is a bold and striking plant. It has stout, upright stems, that are 3-5+ ft. tall. The stems can be sparsely branched, though they are rarely so in the Montrose plants we’ve seen. The leaves are large (to 6 inches long and 3 inches wide), simple, oval-shaped and opposite. The veins are prominent, and the leaves are thick and somewhat succulent. The entire plant is an attractive pastel green; a color that contrasts well with the flowers (or with the darker foliage of background plants). The stems and underside of the leaves may be covered by dense, white hairs.

Showy milkweed (Asclepias speciosa): leaf,
upper surface

Showy milkweed (Asclepias speciosa): leaf,
lower surface

Like most Milkweeds, Asclepias speciosa is a perennial – coming back year after year. It sends up new stems in the spring, spreading via underground stems (rhizomes). In time, a single plant can form a large clump, given favorable conditions. In nature – and in drier gardens – the stems die back after seeds are produced in late summer. In other gardens, plants may persist until frosts kill the stems.

Showy milkweed (Asclepias speciosa): flowering
plant

Asclepias speciosa blooms in late spring to summer; depending on climate and weather, this may be as early as May to as late as July or even August. The flowers of the Showy milkweed are large for the genus. They grow in dense, mounded clusters, usually at the top of the stem, but also in the upper leaf axils (where leaves connect to the stem). Each flower can be up to 1 inch (2.5 cm.) across. The flowers are very fragrant. They attract a wide range of butterflies and other native pollinators.

Showy milkweed (Asclepias speciosa): close-up
of flower, side view

The flowers themselves are rose-pink, fading to cream. The flower shape is typical for the Milkweeds. If you’ve never closely examined a milkweed flower, it’s well worth your time. The flowers are a marvel of Mother Nature’s ingenuity. The flowers look like crowns. The corona (crown-shaped structure above the petals) is composed of five ‘hoods’ and ‘horns’ which are modifications of the male sex organs. In the very center is a complex structure (the gynostegium) composed of fused parts of both male and female organs.

The hoods and horns are appropriately named; as seen above and below, they indeed look like hoods and horns. They point towards the anthers (the pollen producing structures), which are fused to the female stigma (the pollen-receiving structure) to form the gynostegium. For excellent labeled drawings of these structures see reference 5, below.

Showy milkweed (Asclepias speciosa): close-up
of flowers

The pollen is stored as pollen masses (pollinium) rather than separate pollen grains. When a pollinator insect visits the flower, its legs slip into the slits between anthers on the gynostegium. If you look closely, you can see these slits in the picture above; there are 5, radiating out from the very center of the flower. When the leg is removed, it takes with it a pollinium, which is deposited into the stigmatic slit of the next flower. From then on, it’s fertilization as usual.

Given the unusual flower structure, you might expect pollination to occur only rarely. Quite the contrary: the highly modified structures, and the lure of sweet nectar, ensure that Milkweed pollination is highly efficient. For more on pollination see: http://mother-natures-backyard.blogspot.com/2013/06/life-friendly-gardening-planning-for.html .

Milkweed (Asclepias): butterflies can function as
pollinators, but they're not as efficient as bees

Showy Milkweed is semi-incompatible, producing few viable seeds if self-pollinated. Where plants are plentiful (like Western Colorado), seed production is rarely a problem; but if you’re growing Showy Milkweed elsewhere, you’ll need to plant several plants, if you want fertile seeds. The pollinators include a wide range of butterflies (not just Monarchs). But the bees, including bumblebees, are often the most important pollinators. If you enjoy watching insect pollinators, this is a plant to consider.

Showy milkweed (Asclepias speciosa): young
seed pods

Showy milkweed (Asclepias speciosa): developing

seed pods

The seedpods are 3-5 inches long, inflated, and may be smooth or spiny (the local ones are spiny – but not sharp to the touch). As seeds develop, the pods dry from a pale green to tan. When fully dry, the pods split along their seams, releasing numerous dark-brown seeds with silky ‘tails’.

Showy milkweed (Asclepias speciosa): sometimes
reseeds in inconvenient places (just pull them up)

The seeds are wind-dispersed, so you may find new patches growing in favorable locations. If plants appear in inconvenient places, just remove them (or remove the seed pods before they fully develop). But if you want to collect the seeds, watch the pods closely. The ripe pods can be collected into a paper bag; the pods will then open in the closed bag, releasing the seeds. The fluffy awns (‘tails’) can then be removed by vigorously shaking the bag. You can then release the ‘fluff’; the heavier seeds will remain at the bottom of the bag. Plant seeds in fall or spring.

Showy milkweed (Asclepias speciosa): seedlings

Showy milkweed is fairly easy to grow (either from plants or seed), if given enough water. Asclepias speciosa grows well in most soil textures, including clays. And it tolerates a wide range of soil pH (about 5.0 to 8.5). Its alkalinity tolerance likely explains its common occurrence on the Western Slope.

It succeeds in full sun to part-shade, but often looks its best in full sun. Consider the location carefully before planting; plants have a long taproot and resent being moved after becoming established. And don’t worry if plants don’t look very impressive when small. Many native perennials need a little time to develop their full character, and this is one of them.

Showy milkweed (Asclepias speciosa): can be grown
with non-native plants that have the same requirements

Showy milkweed does need average to moist soils, at least until after flowering is completed and seed pods are well developed. If you live in a dry area (or you’re experiencing a dry spell) supplemental water will be required. Once the seeds have dispersed, you can safely let the ground dry out. Cut back the dry stems in fall or winter. That’s really about all that’s needed – you won’t even need to fertilize, unless you grow Showy milkweed in a container. And don’t worry about insect pests; slugs and snails are about the only real challenges.

Showy milkweed (Asclepias speciosa):
attractive summer perennial

At this point, you may be wondering how to include Showy milkweed in your garden. It’s hardy in regions from USDA Zones 3a to 9b, and is a great perennial for any moist area: around a garden pond, in rain gardens and infiltration swales, in moist irrigated areas, in mixed meadows etc. It benefits from runoff, so it often does well along driveways, roadsides and around patios. It can even be grown in a large container. It looks particularly good when massed, and can be used mid-bed in mixed flower beds. It shows up particularly well against dark backgrounds, including larger shrubs.

Showy milkweed (Asclepias speciosa): pastel shades
contrast well with darker background foliage

Of course, Showy milkweed is often included in pollinator and butterfly gardens. But you might want to plant it for other reasons. Of all the local Milkweeds, this species produces the lowest concentrations of toxic resinoids, alkaloids and cardiac glycosides (the chemicals for which Milkweeds are famous). Native peoples throughout the Four Corners states used young shoots, stems, flower buds, immature fruits, and roots as cooked greens. That being said, this is a Milkweed – we don’t advocate eating any part of milkweeds.

Not surprisingly, Asclepias speciosa has a long history as a medicinal plant. The milky sap contains antiseptic chemicals. Many native traditions favor it as a topical treatment for skin sores, cuts, warts and ringworm. A poultice of mashed roots is applied to rheumatic joints to relieve pain and reduce swelling. Decoctions (teas) of the roots were traditionally used to treat coughs. As with many natural medicines, Milkweeds should not be taken internally. These are medicines – and all medicines have the potential to be harmful, even lethal.

Showy milkweed (Asclepias speciosa): particularly
effective when mass planted

Showy milkweed was traditionally an important source of fiber for cordage and rope. The fibers were also used in weaving and for making paper. The tough fibers are obtained from dead stalks gathered in the fall. Archeologic evidence suggests this fiber has long been used in Southwestern and California cultures. The silky floss from the seeds was traditionally used to line cradleboards and baby’s diapers. It has also been used to stuff pillows and even life jackets (it’s water-proof). During World War II, gardeners, farmers and school children collected Milkweed floss for the latter use [ref. 6].

Showy milkweed (Asclepias speciosa): habitat
for many interesting insects

So, why consider planting Showy milkweed in your garden? First, it’s an interesting and pretty perennial, bringing bold foliage and pretty flowers to the summer garden. Second, it provides important habitat for interesting insects: butterflies, native bees and colorful Milkweed bugs to name a few. And birds use the fiber for nest building.

Third, it’s an easy plant to grow in many types of soils. Easy to grow perennials are a welcome addition to any garden. But perhaps most importantly, this is a plant with a long tradition of use by inhabitants of the Four Corners states and California. When you grow it – and use it – you become part of a tradition rooted in our Colorado soil and our history. And that’s something that’s hard to trump!