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Got Milk...weed?

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By Judy Sedbrook, Colorado Master GardenerSM, Colorado State University Cooperative Extension, Denver County

The dazzling appearance of Monarchs and other butterflies adds both color and movement to the garden. Sadly, destruction of habitat sites and increased use of pesticides have placed the Monarch in jeopardy.

Monarch larvae feed exclusively on plants of the Asclepiadaceae, or milkweeds . Common Milkweed (A. syriaca) is a native perennial plant found in prairies and pastures, along roadsides, and on the banks or edges of ponds and lakes. It is so named because of the milky sap found in its leaves, stems and pods.

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Butterfly larva on milkweed

As important as milkweed is to Monarchs in their U.S. and Canadian summer habitat, this is only half the story. In fall, the Monarch butterfly migrates to spend the winter in the mountains of Mexico. According to "Monarch Watch", a joint effort by the University of Kansas Dept. of Entomology and the University of Minnesota Dept. of Ecology, mountain forests inhabited by this butterfly have declined from 42 acres in 1996-97 to 32 acres last winter and only an estimated 13.5 acres this year.

Habitat enhancement along the entire length of the Monarch's two migration paths are critical to survival. Colorado is sandwiched between the two paths along the Pacific coast and Midwest/East coast and hosts only "strays."

You can make your garden friendly to Monarchs and more plentiful Colorado dwelling butterflies such as Painted ladies and Colorado hairstreaks. Gardening practices that affect butterflies include overuse of pesticides, amount of nectar producing plants for adults and food plants for butterfly caterpillars.

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Butterfly on milkweed

For Monarchs, milkweed is the caterpillar food.

Common Milkweed is hardy in zones 3-8 and grows 2 to 5 feet high. Thriving in full sun to partial shade, it can be grown in all types of soil. Because it requires minimal amounts of water, milkweed makes a good addition to the xeriscape garden.

The opposite, dark-green leaves of Common milkweed are large, 6-8 inches in length and 2-4 inches wide. Its very fragrant, pink blossoms grow in large, rounded, umbrella-like clusters and are a good source of nectar for adult Monarchs.

In autumn, the flowers develop into spindle-shaped pods, 2-4 inches long. When dry, the pods crack open to disperse fluffy clumps of silk with flat, brown seeds. The silk, actually a tiny tube filled with air, was used to fill life jackets in WWII and is still used to fill natural fiber pillows.

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Milkweed Seedpod

Because the seeds so easily become airborne, pods should be discarded before they dry to avoid the spread of plants to areas of the garden where they are unwelcome.

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Milkweed seeds

A native American remedy, and historically used in patent medicines, the milkweed plant is mildly toxic and will cause vomiting and diarrhea if ingested. The milky sap can cause irritation if it comes into contact with the eyes.

Other varieties of milkweed that adapt well to the garden are the orange flowered Butterfly Weed (A. tuberosa), Yellow Milkweed (A. tuberosa 'Hello Yellow'), Blood Flower Milkweed (A. curassavica) and pink-purple flowered Swamp Milkweed (A. incarnata).

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Butterfly Weed

Swamp Milkweed

Blood flower Milkweed

'Hello Yellow'

For more information on butterfly gardening see CSU Fact Sheet 5.504, Attracting Butterflies to the Garden.

For the latest research on the plight of the Monarch, see Monarchs and Bt corn.

Photographs by Judy Sedbrook.
Photograph of larva on milkweed courtesy of Martin Schwalbaum

Seed, plant and information sources:

Butterfly Encounters

Prairie Frontier

Prairie Nursery

Garden.com

Monarch Watch

Sheffield's Seed Co., Inc.

Johnny's Selected Seeds

For more information on butterfly gardening see CSU Fact Sheet 5.504 Attracting Butterflies to the Garden.

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Date last revised: 01/05/2010