Feed Your Monarch Butterflies This Year

This week, we are highlighting our milkweeds, which provide food for Monarch butterfly caterpillars. The population of Monarchs has dropped precipitously to less than 1% of the population size in the 1980s and is now under consideration for listing as a federally endangered species. A recent study found pesticide residues at concentrations lethal to Monarchs in 32% of milkweed samples from California’s Central Valley. This study highlights the importance of having pesticide-free forage for pollinators. We currently have five varieties of certified organic milkweeds for sale. The California Natives include Narrowleaf and Showy milkweeds. From the East Coast, we have Swamp and Common milkweeds. We also offer Tropical milkweeds for sale (more about those later). We’d love to get these certified organic pollinator-friendly plants into your gardens to feed the Sonoma County monarchs, so stop by and pick up some plants!

Monarchs and Milkweed

Monarch butterflies are the iconic butterfly of North America. The California Monarchs overwinter in the Central Coast region of the state, migrating from the Western U.S. and Canada in the fall. Sadly, this year’s Western Monarch Thanksgiving Count conducted by the Xerces Society revealed critically low numbers of monarchs. In the 1980s, there were an estimated 4.5 million monarchs overwintering in California. In January 2020, the population was counted at 29,418 monarchs—less than 1% of the historic population and below the projected threshold for collapse of the western monarch migration.

Monarchs are dependent on Milkweed to survive as it is the only plant the caterpillars will eat. The sap of the plant renders the caterpillars toxic and bad-tasting to birds, which protects them somewhat from predators. The Monarchs have adapted to this toxic sap and lay their eggs only on this plant.

Over the last 25 years, changes in agricultural practices have led to a dramatic reduction in Monarch habitat. The decline is partially due to the increase in use of genetically modified herbicide-resistant crops, where routine spraying kills everything but the resistant plants. The June 2020 study from the University of Nevada, Reno shows that the milkweeds in the Central Valley of California are also contaminated with insecticides, fungicides, and herbicides at levels toxic to Monarchs, suggesting that other pesticides are a likely contributor to the population declines as well.

Why We Plant Tropical Milkweeds and Native Milkweeds

The Milkweed plant is the sole host plant for Monarch butterflies, with the adult butterflies feeding on nectar from the flowers and the caterpillars dining on the leaves in late summer/early fall, forming a chrysalis, and hatching out into a new butterfly in mid to late fall in time to migrate to coastal areas for overwintering.

There are many different species of milkweed plants that Monarch caterpillars will gladly eat. What we have found here in Sonoma County is that the CA native milkweeds tend to bloom and die back early in the season and are sometimes gone before our Monarchs arrive. Last year (2019) was especially extreme—the Monarchs didn’t show up until late October and most of our native milkweeds were long gone. However, the Tropical milkweeds keep blooming until frost kills them, which makes them available the full season. We also had some Tweedia in the field, a member of the milkweed family, and we ended up hatching out about 30 mature butterflies in mid-November, after feeding them on Tropical milkweeds and Tweedia! While the tropicals can be a route for disease transmission in southern latitudes, there would be no butterflies at all if they don’t have something to eat. For this reason, we have both native and non-native milkweeds on the property. More information about milkweed differences and how they impact Monarchs can be found on the Xerces Society website. They provide extensive material on Monarch Butterflies.