Milkweeds: Not Just for Monarchs

Monarch on milkweed

When we think of milkweeds, we typically think in terms of those plants that Monarch butterflies eat. And yes, Monarch larvae are dependent on milkweeds. The leaves contain toxic chemicals (cardenolide) that the insects feeding on them can incorporate into their own bodies, making them unpalatable to predators.

But there’s more to milkweeds than just as fodder for caterpillars. In fact, there are over 200 species. Some are desirable perennials that add flowers in shades of brilliant orange and yellow to a Colorado border. Others are Colorado wildflowers. When it comes to milkweeds, it pays to look a bit closer.

I probably have way too much catmint planted throughout our landscape, so I’m always looking for suitable companion plants. In some areas, I’ve chosen similar hues—pinks and blues—to create a soothing effect, while in other spots I aimed for maximum contrast—bright yellows and vivid oranges. One of my favorite picks is Butterfly Weed.

Butterfly Weed (Asclepias tuberosa) is a medium-sized perennial with yellow to orange flowers, bright green leaves, and showy seed pods. Not only is it hardy to zone 3, mine have survived sudden freezes such as the one a couple of years ago, when the temperature abruptly plummeted from daytime highs in the 70s to an overnight low of 11° F!

These are eastern wildflowers, so I expected them to need abundant irrigation. They do need a bit more water than we get naturally in Colorado, but I was delighted to find that they tolerates drier soil as well.

Choose a site that gets at least six hours of sun. If you grow the plants from seed, be prepared to wait several years for them to bloom. You can also transplant seedlings, being careful of their tap roots. Don’t disturb them once they’re established. In our dry climate, the plants are definitely low maintenance, avoiding the fungal diseases more common in humid areas.

The flowers have an abundant supply of nectar, so as you might expect, Butterfly Weed attracts several species of butterflies—and bees, hummingbirds, and other pollinators. However, perhaps due to their lower levels of cardenolides, they aren’t a monarch’s first choice for dinner.

I planted Butterfly weed in my pollinator garden, where they keep company with Agastache, stonecrop, coneflowers, and of course catmint.

Showy Milkweed (A. speciosa) grows in abundance throughout the western U.S. and Canada. Reaching up to six feet in height, it’s hard to miss, especially when it’s covered with its distinctive dusty-pink flowers. Hardy in zones 3 – 9, it prefers moist soil but will survive on much less.

Showy Milkweed is one of the species sold as seed by those promoting butterfly conservation. Not only do monarchs use it both as a host plant and a nectar source, but the flowers attract a wide variety of other pollinators, including fritillaries, queens, checkerspots, hairstreaks, swallowtails, and painted lady butterflies, as well as sphinx moths, bees, lacewings, and hummingbirds.

Seedlings are available online and sometime in local nurseries, but most gardeners start from seed. The seeds need a cold treatment; plant outside in fall or early winter, or stratify the seeds in the freezer for a couple of months before germinating at room temperature.

Swamp Milkweed (A. incarnata) is similar in appearance to Showy Milkweed, but prefers wetter soil, making it less suitable for most Colorado gardens. Consider it if you have a swampy spot in your yard.

The first time I encountered it (while birding in southeastern Colorado), I didn’t recognize Asclepias subverticillata as a milkweed. Then I realized it had the familiar flowering umbels and distinctive milkweed flower shape of five reflexed petals and an elevated central crown. Known as horsetail milkweed or whorled milkweed, it’s a common western wildflower. Like other milkweeds, the leaves are poisonous—a problem for ranchers, but a benefit to a variety of caterpillars, including monarchs.  It’s bloom time in late summer makes it an essential late-season host.

With so many options, surely there’s a milkweed for every garden.

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