Which Milkweed is Best for Monarchs?

If you want to help increase the Monarch population, milkweed is the first plant you should consider adding to your garden. Milkweed is the only plant that Monarch caterpillars eat. Without milkweed, there would be no Monarch caterpillars, and without Monarch caterpillars, there would be no Monarch butterflies, and without Monarch butterflies, there wouldn’t be any eggs that Monarch caterpillars hatch from. You get the picture? There may be many factors that have caused the Monarch population to decline so significantly, but if there is one thing that we can do to keep them from going extinct, it is to plant milkweed. It used to be widely distributed throughout North America, but as we keep taking vacant land and turning into sprawling urban areas; housing subdivisions; condo and apartment complexes; industrial and technology parks; farms; and roads, there has been a significant decrease in this key Monarch plant.

With over 1000 species of milkweed around the world, which is the best for your garden? The first thing to consider is where you live. Not all species of milkweed will survive in all climates. For example, Butterfly Weed (a type of milkweed) thrives in our garden in the upper Midwest of the US, but would not survive the hot summers in southern Florida. Whenever possible, I recommend planting native plants in your garden. A native plant is one that has occurred naturally in a particular region without human introduction. Throughout this article, I will discuss several of the different milkweed species and their various attributes so that you can pick out the best milkweed for Monarchs in you particular area.

Before we dive into the different types of milkweed, let’s get some of the sciencey stuff out of the way. The scientific name of milkweed is Asclepias. The different species of milkweed will start with Asclepias, followed by a second word for the particular type of milkweed. For example, Asclepias syriaca is a specific species of milkweed. In addition to their scientific names, they also have common names which are much easier to remember (and pronounce). For example, Asclepias tuberosa is the scientific name for the milkweed that we currently have growing in our garden. We call it by one of its common names: Butterfly Weed. Other common names for Asclepias tuberosa include butterfly love, butterfly milkweed, Canada root, chigger flower, chiggerflower, fluxroot, Indian paintbrush, Indian posy, orange milkweed, orange root, orange Swallow-wort, pleurisy root, silky swallow-wort, tuber root, yellow milkweed, white-root, and windroot. When you are looking for milkweed plants, either at your local garden center or online, they will normally list both the scientific and the common names.

Important Notes:

1. If you are looking for milkweed plants at your local garden center, you must make sure that the plants were not treated with pesticides or insecticides, either at the store, or prior to arriving at the store. A lot of times pesticides will be used on plants to kill any insects that may eat or damage the plant. Who wants to go to their local nursery or garden store to buy pretty flowers for their garden only to find them all chewed up? How many of those plants do you think the store would sell? Not many, which is why they are treated with chemicals to kill the bugs, keep the plants in tiptop shape, and make them easier to sell. Unfortunately, if milkweed is treated with those same insecticides or pesticides, it will kill any Monarch caterpillars on the plant, which is exactly what we don’t want.
2. Milkweed is toxic. The sap in the plants contain a toxin called cardiac glycoside. It’s the milkweed’s defense mechanism to keep animals from eating it. If an animal eats a milkweed plant it can be harmful or even fatal, so it is important to keep pets away from milkweed. It can also cause skin and irritation in humans. Care must be taken when incorporating milkweed into your garden. Always wear gloves when handling the plants and wash hands and skin thoroughly if you come into contact with them. By now you are probably asking that if milkweed is toxic, how come Monarch caterpillars are able to eat it? Monarchs actually use the toxins in the milkweed sap as one of their defense mechanisms. As the caterpillars eat the milkweed leaves, the cardiac glycoside is absorbed into their tissue. The toxin is retained in the tissue through metamorphosis so it is also present in the adult Monarch butterfly. Some predators, such as birds, have been found to get sick after eating a Monarch because of this toxin, thereby teaching the bird not to eat Monarchs. The level of toxicity varies between milkweed species, and even between plants of the same species. Some plants are even too toxic for even Monarchs to eat.

I hope the toxicity of the milkweed plants didn’t scare you off. We’ve been growing Butterfly Weed in our garden for a few years now and I only recall having minor skin irritations on my arms after they came into contact with the plants. You just need to be aware that you need to take a little extra precaution with these plants. I guess you can say that it is a necessary evil to save the Monarchs.

Because there are so many different species of milkweed, it would be next to impossible to list and describe them all here. For now I will just list about 30 varieties that can be found around North America.

 

Asclepias albicans

• Common names: Whitestem Milkweed, Wax Milkweed
• Native Range:
  • USA: Arizona, California (Sonoran and Mojave Deserts)
  • Mexico: Baja California
• USDA Hardiness Zones: 9a to 11

Asclepias amplexicaulis

• Common names: Bluntleaf Milkweed, Blunt-leaved Milkweed, Clasping Milkweed
• Native Range:
  • USA: Alabama, Arkansas, Connecticut, District of Columbia, Delaware, Florida, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Nebraska, New Hampshire, New Jersey, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, Road Island, South Carolina, Tennessee, Texas, Vermont, Virginia, West Virginia, Wisconsin
• USDA Hardiness Zones: 3b to 9b

Asclepias angustifolia

• Common name: Arizona Milkweed
• Native Range:
  • USA: Arizona
• USDA Hardiness Zones: 8b to 10a

Asclepias asperula

• Common names: Antelope Horn Milkweed, Green-flowered Milkweed, Spider Milkweed (Note that Green Milkweed and Spider Milkweed are also common names for Asclepias viridis)
• Native Range:
  • USA: Arizona, California, Colorado, Idaho, Kansas, Nebraska, New Mexico, Nevada, Oklahoma, Texas, Utah
• USDA Hardiness Zones: 7a to 9a

Asclepias californica

• Common name: California Milkweed
• Native Range:
  • USA: California
  • Mexico: Baja California
• USDA Hardiness Zones: 7 to 10

Asclepias cordifolia

• Common names: Heart-leaf Milkweed, Purple Milkweed (Note that Purple Milkweed is also a common name for Asclepias purpurascens)
• Native Range:
  • USA: California, Nevada, Oregon
• USDA Hardiness Zones: 7a to 10b

Asclepias cryptoceras

• Common names: Cow-cabbage Milkweed, Humboldt Mountains milkweed, Jewel Milkweed, Pallid Milkweed
• Native Range:
  • USA: Arizona, California, Colorado, Idaho, Nevada, Oregon, Utah, Washington, Wyoming
• USDA Hardiness Zones: 6a to 10b

Asclepias curassavica

• Common names: Tropical Milkweed, Bloodflower (or Blood flower), Cotton Bush, Hierba de la Cucaracha, Mexican Butterfly Weed, Redhead, Scarlet Milkweed
• Native Range:
  • USA: not native
• USDA Hardiness Zones:
• Note: Asclepias curassavica has become a popular milkweed plant in the southern coastal areas of the United States. However, this is not a native milkweed to the United States so I do not recommend planting this. I only recommend planting milkweed that is native to your area.

Asclepias eriocarpa

• Common names: Woollypod Milkweed, Indian Milkweed, Kotolo Milkweed
• Native Range:
  • USA: California, Nevada (western border)
  • Mexico: Baja California
• USDA Hardiness Zones: 4 to 9

Asclepias erosa

• Common names: Desert Milkweed (Note that Desert Milkweed is also a common name for Asclepias subulata)
• Native Range:
  • USA: Arizona, California, Nevada, Utah
  • Mexico: Baja California
• USDA Hardiness Zones: 4 to 10

Asclepias exaltata

• Common name: Poke Milkweed
• Native Range:
  • Canada: Ontario, Quebec
  • USA: Alabama, Connecticut, Delaware, Georgia, Illinois, Indiana, Iowa, Kentucky, Maine, Maryland, Massachusetts, Michigan, Minnesota, New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee, Vermont, Virginia, West Virginia, Wisconsin
• USDA Hardiness Zones: 3a to 9b

Asclepias fascicularis

• Common names: California Narrowleaf Milkweed, Mexican Whorled Milkweed, Narrow-leaf Milkweed, Narrow Leaved Milkweed
• Native Range:
  • USA: California, Idaho, Nevada, Oregon, Utah, Washington
• USDA Hardiness Zones: 6 to 10

Asclepias hirtella

• Common names: Prairie Milkweed, Tall Green Milkweed (Note the Prairie Milkweed is also a common name for Asclepias sullivantii)
• Native Range:
  • Canada: Ontario
  • USA: Alabama, Arkansas, Georgia, Iowa, Illinois, Indiana, Kansas, Kentucky, Louisiana, Michigan, Minnesota, Missouri, Ohio, Oklahoma, Tennessee, West Virginia, Wisconsin
• USDA Hardiness Zones: 4 to 9

Asclepias humistrata

• Common names: Pinewoods Milkweed, Sandhill Milkweed 
• Native Range:
  • USA: Alabama, Florida, Georgia, Louisiana, Mississippi, North Carolina, South Carolina
• USDA Hardiness Zones: 8a to 9b

Asclepias incarnata

• Common names: Pink Milkweed, Swamp Milkweed
• Native Range:
  • Canada: Manitoba, New Brunswick, Nova Scotia, Ontario, Prince Edward Island, Quebec
  • USA: Alabama, Arkansas, Colorado, Connecticut, District of Columbia, Delaware, Florida, Georgia, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Missouri, Montana, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Utah, Vermont, Virginia, West Virginia, Wisconsin, Wyoming
• USDA Hardiness Zones: 3a to 8b

Asclepias linaria

• Common names: Needle-leaf Milkweed, Pineneedle Milkweed, Pine-needle Milkweed
• Native Range:
  • USA: Arizona,California, New Mexico
• USDA Hardiness Zones: 9a to 11

Asclepias nyctaginifolia

• Common name: Mojave Milkweed
• Native Range:
  • USA: Arizona,California, New Mexico, Nevada
• USDA Hardiness Zones: ?

Asclepias oenotheroides

• Common names: Hierba De Zizotes, Lindheimer’s Milkweed, Longhorn Milkweed, Primrose Milkweed, Side-cluster Milkweed, Zizotes Milkweed
• Native Range:
  • USA: Arizona, Colorado, Louisiana, New Mexico, Oklahoma, Texas
• USDA Hardiness Zones: 7a to 9b

Asclepias ovalifolia

• Common names: Dwarf Milkweed, Oval-leaf Milkweed
• Native Range:
  • Canada: Alberta, Manitoba, Ontario, Saskatchewan
  • USA: Illinois, Iowa, Michigan, Minnesota, Montana, North Dakota, South Dakota, Wisconsin, Wyoming
• USDA Hardiness Zones: 3 to 5

Asclepias perennis

• Common name: Aquatic Milkweed
• Native Range:
  • USA: Alabama, Arkansas, Florida, Georgia, Illinois, Indiana, Kentucky, Louisiana, Missouri, Mississippi, South Carolina, Tennessee, Texas
• USDA Hardiness Zones: 6a to 9b

Asclepias purpurascens

• Common name: Purple Milkweed (Note that Purple Milkweed is also a common name for Asclepias cordifolia)
• Native Range:
  • Canada: Ontario
  • USA: Arkansas, Connecticut, District of Columbia, Delaware, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Nebraska, New Hampshire, New Jersey, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, Rhode Island, South Dakota, Tennessee, Texas, Virginia, West Virginia, Wisconsin
• USDA Hardiness Zones: 3a to 9b

Asclepias solanoana

• Common names: Prostate Milkweed, Serpentine Milkweed, Solanoa
• Native Range:
  • USA: California
• USDA Hardiness Zones: ?

Asclepias speciosa

• Common name: Showy Milkweed
• Native Range:
  • Canada: Alberta, Saskatchewan
  • USA: Arizona, California, Colorado, Idaho, Illinois, Iowa, Kansas, Michigan, Minnesota, Montana, Nebraska, Nevada, New Mexico, North Dakota, Oklahoma, Oregon, South Dakota, Texas, Utah, Washington, Wisconsin, Wyoming
• USDA Hardiness Zones: 3a to 9b

Asclepias subulata

• Common names: Ajamete, Desert Milkweed, Rush Milkweed (Note that Desert Milkweed is also a common name for Asclepias erosa)
• Native Range:
  • USA: Arizona, California, Nevada
• USDA Hardiness Zones: 9 to 11

Asclepias sullivantii

• Common names: Prairie Milkweed, Sullivant’s Milkweed, Smooth Milkweed (Note the Prairie Milkweed is also a common name for Asclepias hirtella)
• Native Range:
  • Canada: Ontario
  • USA: Arkansas, Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, Oklahoma, South Dakota, Wisconsin
• USDA Hardiness Zones: 4a to 7b

Asclepias syriaca

• Common names: Common Milkweed, Butterfly Flower, Silkweed, Silky Swallow-wort, Virginia Silkweed
• Native Range:
  • Canada: Manitoba, New Brunswick, Newfoundland and Labrador, Nova Scotia, Ontario, Quebec, Saskatchewan
  • USA: Alabama, Arkansas, Connecticut, District of Columbia, Delaware, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, New Hampshire, New Jersey, New York, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Vermont, Virginia, West Virginia, Wisconsin
• USDA Hardiness Zones: 3a to 9b

Asclepias tuberosa

• Common names: Butterfly Weed, Butterfly Milkweed, Chigger Flower, Orange Milkweed, Pleurisy Root
• Native Range:
  • Canada: New Brunswick, Newfoundland and Labrador, Nova Scotia, Ontario, Quebec
  • USA: Alabama, Arizona, Arkansas, California, Colorado, Connecticut, District of Columbia, Delaware, Florida, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Nebraska, New Hampshire, New Jersey, New Mexico, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Utah, Vermont, Virginia, West Virginia, Wisconsin
• USDA Hardiness Zones: 3a to 9b

Asclepias variegata

• Common names: Redring Milkweed, White milkweed, White-flowered Milkweed
• Native Range:
  • Canada: Ontario
  • USA: Alabama, Arkansas, Connecticut, District of Columbia, Delaware, Florida, Georgia, Illinois, Indiana, Kentucky, Louisiana, Maryland, Mississippi, Missouri, New Jersey, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, South Carolina, Tennessee, Texas, Virginia, West Virginia
• USDA Hardiness Zones: 3a to 9b

Asclepias verticillata

• Common names: Eastern Whorled Milkweed, Horsetail Milkweed, Whorled Milkweed
• Native Range:
  • Canada: Manitoba, Ontario, Saskatchewan
  • USA: Alabama, Arizona, Arkansas, Conneticut, Delaware, District of Colombia,  Florida, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maryland, Massachusetts,  Michigan, Minnesota, Mississippi, Missouri,  Montana, Nebraska, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Vermont, Virginia, West Virginia, Wisconsin,  Wyoming
• USDA Hardiness Zones: 3a to 9b

Asclepias vestita

• Common name: Woolly Milkweed
• Native Range:
  • USA: California
• USDA Hardiness Zones: 7a to 10b

Asclepias viridis

• Common names: Green Antelopehorn, Spider Milkweed (Note that Green Milkweed and Spider Milkweed are also common names for Asclepias asperula)
• Native Range:
  • USA: Alabama, Arkansas, Florida, Georgia, Illinois, Indiana, Kansas, Kentucky, Louisiana, Mississippi, Missouri, Nebraska, Ohio, Oklahoma, South Carolina, Tennessee, Texas, West Virginia 
• USDA Hardiness Zones: 4b to 9b