Q. Where and when can I see flowering milkweed plants around Flagstaff?
A. Green and maroon Asclepias asperula (“Antelope Horns”) is already blooming in the Coconino National Forest. You can see the white horsetail variety (A. subverticallata) along the trails at Buffalo Park.
The orange milkweed (A. tuberosa), known as Butterflyweed, is a treat to find in the wild — I came across one blooming on the south-facing slopes of Mt Elden last August. Pink-and-white A. speciosa, called Showy Milkweed, occurs sporadically in northern Arizona but is not as common here as in other parts of the west. Once established in a Flagstaff garden, however, it will flourish. There’s a patch on the grounds of Riordan Mansion, and of course at the Arboretum.
Milkweeds are a trending topic because of their relationship with butterflies, especially monarchs. As noted in the Daily Sun’s June 29th article about the Arboretum’s butterfly house, monarch butterfly populations are in sharp decline, and many scientists attribute this to loss of the monarchs’ habitat. Butterflies need specific plants for food and for reproduction.
While all butterflies visit a variety of flowers to sup nectar, they are particular about the plants they choose for a nursery. A female butterfly will deposit her eggs on the leaves of only one or two particular plant species. This ensures that her offspring, whom she will never see, will have the proper food source once they hatch into hungry, hungry caterpillars.
Monarchs are perhaps the fussiest of all butterfly species: they only lay their eggs on milkweeds. Scientists believe that monarchs choose milkweeds because of the toxicity of these plants. Monarchs are unaffected by the poisonous sap of the milkweeds, but big range animals suffer and can die if they consume milkweed. Because the caterpillars (and later, the emerging adult monarchs) feed exclusively on milkweed leaves, they themselves become toxic. Birds won’t eat the yellow/black Monarch caterpillars or the orange/black adult butterflies once they’ve learned that those individuals taste bad.
Life was great for the monarchs until agriculture came along. Farmers wanted more land for their crops, so they began plowing under the meadows where milkweeds grew. Trucks sprayed herbicides on county roadsides to eliminate unsightly and encroaching “weeds.” And pesticides used by home gardeners as well as by farmers killed caterpillars of all species — an unintended consequence of maximizing our crop yields.
The Arboretum at Flagstaff is leading the local effort to provide habitat and food for the Monarchs who travel through our town. Researchers there have collected seeds from our four kinds of native milkweed: Antelope Horns (A. asperula), Butterflyweed (A. tuberosa), Horsetail Milkweed (A. subverticillata), and Showy Milkweed (A. speciosa).
They’ve planted these seeds in large plots at the Arboretum, in order to attract monarchs there and to provide young milkweed plants for local gardeners. But transplanting these otherwise hardy plants is a challenge, as is growing milkweed from seed. If you wish to attract monarchs to your northern Arizona yard, it’s best to get milkweed that has been raised from seed at the elevation and in the climate that we have here. Once established — which may take a few years — you’ll be rewarded with handsome plants and the knowledge that you are providing habitat for beautiful monarchs.
Here's some breaking news about monarchs’ legal status: in 2014, the Secretary of the Interior received a petition to list monarchs on the Endangered Species list; the US Fish & Wildlife Service promised to make a decision by June 30, 2019. But on May 24, 2019, the agency announced that it would delay its decision until December 15, 2020.
In the meantime, plant milkweed in your garden, but use caution. Keep in mind that eating these plants can make you or your animals sick. If only we were as hardy as those monarchs!