MONARCHS AND MILKWEED: in the Urban Garden

By Stacy Diamond

There is no closer relationship in nature than that which exists between the monarch butterfly and its host plant, milkweed, but the majestic orange and black pollinator is now in dire peril. Monarchs have been seeing population declines as steep as 80-90% over the last 20 years, while an astounding estimated 40% of all insect species are threatened with extinction.

The tragic decline of this iconic pollinator species due to milkweed depletion is the direct result of careless agricultural methods. The scattered stands of the plant that once grew in abundance among crops, between rows of corn, and in wild meadows have been virtually eliminated by the widespread use of herbicides, particularly the widespread use of Roundup weedkiller. The fact that these conditions still prevail throughout the Midwestern US mean catastrophic consequences for our ecosystems.


The monarch lays a single dome-shaped egg on the underside of a milkweed leaf. After about five days the newborn caterpillar appears and immediately begins to eat its fill of the leaf upon which it was hatched. Bite after bite, the leaves are consumed from each stalk. The caterpillar becomes brightly colored with black stripes on a yellow body. Long antennas protrude from both ends. After about two weeks the caterpillar has gained weight and has grown in size. The sun has imparted light to brighten his colors and increase his size. Then follows a great deal of activity as the time for metamorphosis approaches. The caterpillar will find a shady branch on which to rest until the midday heat has passed. Then it attaches itself with a pad of spun silk to the underside of a milkweed leaf. The pale green chrysalis spotted with gold lives unseen within the caterpillar. During the night, hanging upside-down until the precise moment, the caterpillar will shed its striped skin in a miraculous metamorphosis.In the morning we see the corporeal has at last turned to the ethereal and the monarch is drying and unfurling its wings. The monarch can be released over beds of blue iris to fly into the elm tree’s branches or the quiet of the sky.


Monarchs are the only butterflies that migrate roundtrip. Weighing no more than a feather, the monarch (Danus plexippus) flies up to 3,000 during a migration that is completed over multiple generations: the eastern population flies to Mexico, the western population splits in two, with some going south to Mexico and others to California. Then, during the spring and summer, monarchs fly to their breeding territory east of the Rocky Mountains and into Canada to find milkweed, the only plant on which the butterfly lays its eggs and the only plant on which the caterpillar feeds. The butterflies fly south in late summer to overwinter in the fir tree forests of central Mexico. The study of monarch migration is still in its early stages and we do not yet know how they navigate. Perhaps they follow along the earth’s magnetic field, as do some species of birds.


Native to North America, the common milkweed (asclepias syriaca) is the monarch’s host plant. It is a herbaceous perennial that flowers in the summer, sets seeds in the Autumn, dies back and goes dormant during the winter months to sprout again in the springtime. The flowers – white, orange, pink and yellow – help support a wide variety of pollinators, which are known as essential for maintaining a healthy food chain. Native milkweed plants also attract beneficial insects such as parasitic wasps, carnivorous flies and predatory bugs, which in turn are helpful in suppressing common garden pests, notably aphids, leafhoppers and stink bugs. For many, milkweed is a beautiful addition to the garden in its own right..

HOW CAN WE HELPOne study reports a 21% decrease in milkweed in the United States between 1995 and 2013. Aside from the hazard of vanishing milkweed, the monarch caterpillars fall prey to numerous predators. In addition to planting milkweed there are a variety of wildflowers that can help foraging butterflies. These species are important to include in our gardens because by the time Autumn rolls around, all the native milkweed species have finished blooming. These flowers offer the monarchs a variety of nectar sources to fuel their migration.

The National Wildlife Federation identified these 12 species as the best to plant for monarchs:

  • Common Milkweed (Asclepias syriaca)
  • Butterflyweed (Asclepias tuberosa)
  • Swamp Milkweed (Asclepias incarnata)
  • Antelope-horns Milkweed (Asclepias asperula)
  • Purple Milkweed (Asclepias purpurascens)
  • Showy Milkweed (Asclepias speciosa)
  • California Milkweed (Asclepias californica)
  • White Milkweed (Asclepias variegata)
  • Whorled Milkweed (Asclepias verticillata)
  • Mexican Whorled Milkweed (Asclepias fascicularis)
  • Desert Milkweed (Asclepias erosa)
  • Green Milkweed (Asclepias viridis)]

Conservationists from a number of organizations recommend planting milkweed in gardens and yards.

See the website of the Xerces Society to source native milkweed seeds appropriate for areas outside of New England. Four types that are particularly recommended for our area are the Common Milkweed; Butterfly Milkweed (A. tuberosa); Poke Milkweed (A. exaltata); Swamp Milkweed (A. incarnata). If you plan to collect milkweed seeds look for the grey-brown pods, not the green ones. It is also advisable to wear gloves and avoid touching your face as the milky sap irritates the skin and may injure your eyes. For more details on gathering milkweed seed for planting, see the USFWS’s National Wildlife Refuge Service webpage.

If you already have milkweed plants, save the seed pods in your refrigerator for the next spring planting; give away pods if you don’t want to plant the seeds yourself. If removing milkweed from your garden, wait until late autumn when all butterfly eggs have hatched and the butterflies have flown off. If you are pulling up milkweed, use care to keep the roots intact so they can be transplanted: the roots are deep and the stems tend to be fragile. The plants also spread extensively underground by rhizomes and can create large stands. A large number and variety of pollinators visit the plants and many species of birds eat the seeds. Common Milkweed is the species preferred by monarchs so we ask: is it invasive?  Answer: Not at all.Some indigenous (aka native) plants are certainly more aggressive than others, but that does not make them invasive. Sometimes aggressive native plants are exactly what you need to replace truly invasive plants that have been introduced from other ecosystems. 

With some care and attention, it is possible to learn to raise butterflies: keep the eggs safe, nurture the caterpillars from chrysalis to newborn butterfly, and to release the monarch into its native habitat. With only an estimated 2%-8% of monarchs surviving from egg to adult, raising even a few monarchs to release back into the environment can help. Anyone interested can look for eggs or caterpillars in the wild. 

 More information can be found on the following websites: Southwest Monarch Study

Peninsula Point Monitoring Project –


Monarch Alert – – butterfly identification

US Fish and Wildlife Service

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