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Monarchs and Milkweed

Monarch butterflies are one of the beauties of nature; they are native throughout the US, except for the arid parts of the west. They also have spread to other parts of the world where milkweed is found, including Central America, northern South America, southern Europe, Australia, Malaysia and parts of the Southern Pacific.

Monarchs are dependent on milkweed plants. Plants serve as a host for their eggs and the caterpillars; the caterpillars eat only milkweed. Some milkweed plants also have nectar for adult monarch food as well as for other beneficial insects.

Because of human activities, milkweed plants are on the decline in the US and elsewhere. The population of monarchs has declined as a consequence of the loss of milkweed.

Various organizations in the US have begun an intense drive to replant milkweeds in butterfly-friendly areas. This has become very popular with gardeners and environmentalists and the demand for information about milkweed, along with sources of seeds and plants is high.

There are said to be 73 species of native milkweeds in the US and about 30 of them serve as host plants for the monarch. These types of milkweeds are scattered across the US in various ecological areas. Oklahoma is thought to have about 20 native milkweeds. Because of environmental requirements, some of the milkweeds in Oklahoma are limited in distribution to only 1-2 counties. In the Tulsa region there are about 10 types of native milkweeds used by monarchs. See the table below for our varieties.

For information as to the types of milkweeds in Oklahoma and the counties in which they can be found, go to the  Kerr Center for Sustainable Agriculture website. For information as to which ones to plant, log on to the monarchwatch.org web site which has excellent resources. This site also has suggestions about how to collect seeds. See also Dr. Dwight Thomas' Tall Grass Prairie bolg essay on milkweeds. It has an excellent disussion of types of milkweed and thier reproductive structure and funcion.

As you approach finding and planting milkweeds, remember one thing—monarch caterpillars are voracious eaters and can rapidly strip a plant of leaves. The answer to this problem is to place several plants in your monarch-friendly area.

There are some interesting facts about milkweed which you may not know. All milkweed are perennial if planted in their preferred growing zone; once established they should return yearly from the roots. These plants also produce a large number of seeds which can be collected for next year’s planting. See this reference for how to collect and process milkweed seeds.

The toxin in milkweed is good news and bad news. The bad news is that that the milky sap in the plants is toxic to pets and children if eaten. Some people also develop rashes upon contact with the sap.

The good news is that the toxin has no adverse effect on the monarch butterfly. They accumulate the toxin in their bodies and if they are eaten by birds the birds become ill and rapidly learn to avoid not only monarchs, but butterflies which look like monarchs.

One of the current problems in the many areas is that nurseries have had limited numbers of milkweed plants. This should rapidly improve because the demand for plants is high. Seeds of various species are widely available on the internet.

There are a huge number of organizations, such as Monarch Joint Venture which are working together and with the USDA to grow more milkweed and thereby increase monarch butterfly numbers. Join the effort! 

Milkweeds of Oklahoma

Common Name

Scientific name

Location in State

Green antelope horn

Asclepias viridis

Prairies, central and east Oklahoma

Antelope horn

Asclepias asperula

Dry soils of prairies, mostly western OK

White milkweed

Asclepias variagata

Southeast, Arkansas border counties

Common milkweed

Asclepias syriaca

Northwest Ok

Swamp milkweed

Asclepias incarnate

Wet areas statewide

Whorled milkweed

Asclepias verticullata

NE and NW Ok in ditches and road banks

Zizotes milkweed (sidecluster milkweed)

Asclepias oenotheroides

Central and south-central Oklahoma

Showy milkweed

Asclepias speciose

Moist soil of open areas

Tall green milkweed

Asclepias hirtella

Scattered, mostly east

Butterfly weed

Asclepias tuberosa

Northwest Oklahoma

Short green milkweed

Asclepias viridiflora

NE OK prairies, areas with little competition

Broad-leaf milkweed

Asclepias latifolia

Central and west, dry plains

Clasping milkweed

Asclepias amplexicaulis

West central

Sand milkweed

Asclepias arenaria

West

Four leaf milkweed

Asclepias quadrifolia

Most common eastern part of state

Prairie milkweed

Asclepias sullivantii

Northeast and north central prairie

Narrow-leaf milkweed

Asclepias stenophylla

Western half of state

Engelmann’s milkweed

Asclepias engelmanniana

Scattered across state, mostly west

The above are most of the milkweeds in OK, but not all. From The Kerr Center for Sustainable Agriculture’s website