Help Save The Monarchs With These 4 Great Milkweeds

Monarch butterfly on swamp milkweed

Last week, I was manning the booth at the Montgomery County Fairgrounds Demonstration Garden (yes, it’s a mouthful), when someone plopped a tall, spindly plant down onto the table. The plant looked pretty pitiful; the flowers were long gone and the lance-shaped leaves had circular holes in them. But upon closer inspection, I spotted a few lantern-shaped chrysalises and some colorful caterpillars working their way up the stems. The plant was none other than milkweed and the ‘lanterns’ contained baby monarchs in the process of forming.

We placed the milkweed next to a drift of Joe-Pye weed and sat back to see what would happen.

Things aren’t looking up for the monarch butterfly

With a wing-span of over 4 inches, monarch butterflies are considered by many to be the ‘king’ of butterflies. According to the National Wildlife Federation, however, their populations in North America are in steep decline. Over the past twenty years, monarch numbers have plummeted by an astonishing 90 percent, prompting scientists to question what’s happening. They suspect the answer is tied up with milkweed.

Close-up of swamp milkweed, Asclepias incarnata

Why milkweed you might ask? Because milkweed is the host plant for monarchs whose caterpillars will only eat plants in the family. And unfortunately, it has been disappearing, too. Over the last couple decades, large-scale clearing of meadows and prairies for development coupled with heavy pesticide use has resulted in milkweed becoming increasingly scarce, placing in jeopardy the tiny species that depends on it for survival.

The problem is so big that according to one National Public Radio (npr) report, monarch populations overwintering in Mexico that averaged around nine hectares from 1995 to 2002, in 2014 took up less than one.*

A migratory insect

Every spring, thousands of Eastern monarchs begin their annual migration from Mexico to Canada, a journey of roughly 3,000 miles. And every fall, they do the same trip in reverse. The insects stop three times to breed along the way, each time going through four stages of development: egg, larvae (caterpillar), chrysalis and butterfly.

Once they emerge from their chrysalises, the butterflies live for just four to eight weeks, long enough to fly hundreds of miles further north to lay their eggs. Then the stages of development are repeated and the next generation of butterflies continues the journey.

Millions of monarch butterflies flying in Mexico

In all, it takes three generations of butterflies to make it to Canada.

Incredibly, the fourth generation butterfly (born in Canada) lives a bit longer. This is the monarch that migrates back to warmer climates like Mexico. This butterfly lives for six to eight months, long enough for it to start the whole process over again in the spring. (To read more about the monarch butterfly cycle, click here.

Monarchs and milkweeds

The milkweed family, Asclepias, owes its common name to the milky latex that oozes when a stem is snapped. It is composed of more than 100 varieties. Tall and leafy, it bears large balls of vanilla-scented mauve-pink flowers and is commonly found growing in large groups along roadsides, ponds, stream beds and even ditches.

Milkweed plants at the Denver Botanic Gardens

In the fall, the plant’s follicles split open to disperse fluffy white seeds that are carried away by the wind.

Milkweed pod and air-borne seeds

Starting in March, monarch butterflies emerge from their hibernation to find a mate and begin the journey north to find milkweed plants on which to lay their eggs. It takes about 4 days for the eggs to hatch. Once the baby caterpillars emerge, they spend about two weeks eating as many of the plants’ leaves as they can until fully grown. Then they find a place to attach themselves to a stem and begin the process of metamorphosis.

It can take an additional two weeks for the adult butterfly to emerge from the chrysalis.

Monarch caterpillar chrysalis

Aside from habitat and nutrition, the milkweed provides another key benefit to the monarch. As the caterpillars undergo transformation in chrysalis, they ingest toxic chemicals secreted in the plants’ sticky sap. These chemicals, called cardenolides, provide them with a defense against would-be predators such as birds and mice.

Monarch caterpillar munching on milkweed

Specifically, cardenolides are so toxic and bitter tasting to other vertebrate species that many have learned to associate bad taste with the butterflies’ distinctive orange and black markings. Although as adults, monarchs no longer eat milkweed, they are able to sequester the toxins that they ingested as larvae, providing them with protection against many predators during the remainder of their lifespan.

Monarchs’ distinctive colors help ward of predators

Monarch butterflies only lay one egg per leaf, but they lay eggs on lots of leaves and always on more than one plant. They are mini eating machines. Three days after the milkweed arrived to the fair, the caterpillars had devoured the plant they rode in on and in their place hung rows of tiny chrysalises.

Milkweed varieties for your garden

Nowadays there are a number of milkweed and butterfly weed varieties that have been developed specifically for the garden. Available in different colors and flower forms, they add a natural beauty to the garden. Planting a few cultivars will help save the monarchs, too.

Common milkweed, Asclepias syriaca

Ready to save the monarchs with milkweed? Here are some great new varieties to try, available at many local nurseries.

Butterfly Weed, Asclepias tuberosa

This bright orange beauty blooms from May to September. It won Perennial of the Year 2017 for its brilliant flowers, hardy, upright stems and good drought-tolerance. It looks great combined with yellow daylilies or fresh white daisies. And, it especially shines against purple-leaved plants like smoke bush.

Butterfly weed, Asclepias tuberosa

Orange not your thing? Then try ‘Hello Yellow’, available through White Flower Farm.

Asclepias tuberosa ‘Hello Yellow’

Or try a hot-color mix of yellow, gold, orange and scarlet, Asclepias tuberosa ‘Gay Butterflies’ available at White Flower Farm.

Asclepias Gay Butterflies Mixture

Swamp Milkweed, Asclepias incarnata

Similar in shape to roadside milkweed, Swamp milkweed ‘Cinderella’s’ deep pink flowers with white centers make it a standout in the garden. And its vanilla-scented flowers are a treat for the senses. Growing 3′ to 4′ tall, it blooms all summer with regular deadheading.

Swamp milkweed ‘Cinderella’ available at

Milkweed generally blooms from June to August. All varieties need full sun and well-drained soil. If you observe caterpillars or chrysalises on your plant, wait until the butterflies have flown away, then simply cut the plant to the ground.

* Monarch populations are measured in hectares, which roughly equal 2 1/2 acres.


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