Skip to main content

Saving Milkweed for Monarch Butterfly caterpillars

University of Illinois Horticulture Educator, Kelly Allsup encourages gardeners to collect seeds from milkweeds to add this much needed plant to the landscape for Illinois monarchs. Kelly warns that you may see butterfly enthusiasts along roadsides collecting seeds from coveted weeds and prairie plants known as the milkweeds this fall.

The milkweed species in Illinois is required for monarch caterpillars; it's the only plant species they will eat. The strategy of monarchs to eat milkweed —a poisonous plant —has helped monarchs avoid being eaten by predators, but has also proved detrimental because of the continual decline of this vital plant. Once covering vast prairies of Illinois, more than 100 milkweed species must now compete with agriculture, invasive plant species and a bad reputation of being a "weed."

It's easy to spot a milkweed plant on the side of the road when the seed pods are forming and maturing. They usually have fat, fleshy leaves, with bright orange, pink or white clustered flower heads glowing during the peak of summer. Common milkweeds have large, round heads and can be hard to transplant from roadsides because of taproots. Swamp milkweeds thrive in garden settings and orange butterfly weed can commonly be found in nurseries as plants for purchase. Each pollinated milkweed flower can produce two pods, but usually only produces one rather large teardrop-shaped green pod. The pods start to turn darker brown or maroon colored and will split open when mature.

Monarch enthusiasts are collecting the seeds so that they may add milkweeds to their butterfly gardens. Seeds can't germinate if they have not been allowed enough time to mature on the plant. Pods should already have started to split open, or when squeezed it easily opens and seeds should be dark in color.

Once pods have been allowed to dry, the seeds can be separated by holding one end and stripping the seeds away from the floss with your fingers. The floss is the white fluff that will float off in the wind. It used to be used as pillow and blanket stuffing. Another way to separate the mature seeds from the floss is to place the seeds in a paper bag with a coin. Cut a hole in the bottom of the bag so the seeds fall out after a good shaking.

Gardeners should store seeds in a dry and cool place in a labeled paper envelope with species, date and location. Milkweed seeds need to be stratified (that is, the seed coat needs to be chilled to germinate). This stratification can be accomplished by placing seeds in a moist paper towel in the refrigerator for about four to six weeks. Start seed germination in early April to have them ready for planting in the garden after the last frost-free date of May 10-15. For more information on milkweeds and monarchs, go to