More Milkweed for Monarchs

At Tanner Spring Park we are hoping to expand the Western breeding habitat for Monarchs by increasing Showy Milkweed. Monarchs migrate through Portland, as well as the northern Oregon coast but have not found significant host plants to breed. We are hoping to change this. The park is part of a national campaign to support the Monarch Butterfly (Danaus plexippus) by growing  Showy Milkweed (Asclepias speciosa). This campaign hopes to reverse the population declines observed across the country. Since monitoring began 20 years ago, overwintering  populations have declined by 74% in coastal California and more than 80% in central Mexico. Several factors contribute to this decline. Loss and degradation of breeding habitat is believed to be a key factor. Milkweed is an essential host plant for egg laying. Adult females lay eggs singly on milkweed species (primarily Asclepias spp., but occasionally on other closely related species as well, including Gomphocarpus spp. and Calotropis spp.), which the caterpillars rely upon for energy and protective toxins called cardenolides. Milkweeds are critical for successful development of the caterpillar into an adult butterfly.

An epic migration, on the verge of collapse. In the 1990s, nearly 700 million monarchs made the epic flight each fall from the northern plains of the U.S. and Canada to sites in the oyamel fir forests north of Mexico City, and more than one million monarchs overwintered in forested groves on the California Coast. Now, researchers and citizen scientists estimate that only a fraction of the population remains, a decline of more than 80% has been seen in central Mexico and a decline of 74% has been seen in coastal California. (Taken from

In 2014 Tanner Springs Park began with only a handful of Showy Millkweed plants. Well suited to dry sunny conditions, the milkweed is increasing each season and becoming a more structural element in our landscape. They are very obvious amongst the prairie grasses. Tall, thick stems support prehistoric-looking giant seed pods in late summer. Upon maturity, the pods dry and crack open, for the  seeds to be dispersed. On a windy day seeds are carried off in the air by an umbrella of silky plumose hairs and can travel for miles. We haven’t spotted any Monarchs passing through our park to feed yet.  But, when they do, we hope they decide to breed as well.

Help support pollinators

You can support pollinators by planting Showy Milkweed in your gardens or planters. Xerces Society for Invertebrate Conservation has created a comprehensive national directory of milkweed seed vendors to help locate sources of seed. To learn more about monarch butterflies and how to participate in conservation efforts, please visit the Xerces Society’s Monarch Butterfly and Western Monarch Conservation Campaign pages or the Monarch Joint Venture webpage.

Be a community scientist and help researchers

Help researchers track Milkweeds and Monarchs across the West to aid conservation efforts. The new Western Monarch Milkweed Mapper is a website and associated database to map sightings of Milkweed and Monarchs across the West. Consider contributing to this community science project while traveling or on a hike. This collaborative effort by Xerces and  Idaho Department of Fish and Game, and Washington Department of Fish and Wildlife, with funding from a U.S. Fish and Wildlife Service State Wildlife Grant and the National Fish and Wildlife Foundation is built upon the efforts of many engaged individuals and agencies. Xerces provides community scientists with comprehensive information on Western Monarch biology, Milkweed  biology, identification, as well as  photography tips to give a beginning scientist the tools to be successful.