If you still see monarch butterflies (Danaus plexippus) in your garden in October in Canada, they are probably latecomers. The great migration of these insects, emblematic of the decline of our ecosystems, to Mexico begins in August and continues until early October, depending on the region.
It is a special generation that makes this journey: while summer monarchs live only 2 to 6 weeks, this generation can live up to eight months, allowing them to travel up to 5,000 km to reach the oyamel pine (Abies religiosa) forests in the mountains of Michoacán and the State of Mexico.
In this cool, humid climate, the butterflies reduce their metabolism and enter reproductive diapause for the winter. Gathered in their millions, forming huge clusters on branches and trunks, they conserve heat and moisture, limiting energy loss and protecting themselves from frost.
In February and March, with the return of longer days and milder temperatures, the monarchs emerge from hibernation. They mate and begin their journey north. The females travel up to the southern United States, lay their eggs on milkweed plants, and then die. It is the next generations, born from these eggs, that gradually continue the journey north to Canada, a journey that takes three to four successive generations.
Milkweed is essential to this journey. It is the exclusive host plant for monarch caterpillars: females lay their eggs on it, and the larvae feed on it before transforming into butterflies, capable of continuing the journey over several generations.
No milkweed, no monarchs. It’s as simple as that.
An endangered species
In Canada, the monarch (Danaus plexippus) has been recognized as an endangered species since 2016 under the Species at Risk Act, mainly due to habitat loss, pesticides, climate change, and deforestation in its wintering grounds in Mexico. In the United States, the U.S. Fish and Wildlife Service concluded in 2020 that the species deserves protection under the Endangered Species Act, but its listing has been postponed in favor of species deemed to be higher priority, giving it “warranted but precluded” status for the time being. Internationally, the International Union for Conservation of Nature (IUCN) classified the migratory monarch as an endangered species in 2022, highlighting the dramatic decline of this iconic population.
Which Milkweed Should You Choose for Your Garden?
All milkweeds are useful to monarchs, but they are not all used in the same way. Butterflies prefer common milkweed and incarnate milkweed because they are abundant, easily accessible, and provide caterpillars with a well-balanced diet. Other species, such as tuberous milkweed, tall milkweed, and whorled milkweed, are less popular but still important: each species is adapted to a particular environment and helps expand the habitats available to support monarch migration.
Common Milkweed
Common milkweed (Asclepias syriaca) is the most widespread. Robust and widely used by monarchs, it thrives in full sun, in medium to rich soil, and tolerates drought well. However, it forms vigorous colonies thanks to its rhizomes, which can make it invasive in a small garden. It is best suited to naturalized areas or country gardens.
Marsh Milkweed
The marsh milkweed (A. incarnata), also known as swamp milkweed, is ideal for heavy or wet soils. It grows in dense clumps, has a pleasant fragrance, and attracts a host of pollinators. It is one of the best for monarch reproduction, perfect for riverbanks or poorly drained clay areas.
Butterfly Weed
Butterfly weed (A. tuberosa) is distinguished by its bright orange flowers. It prefers sandy, dry, well-drained soil in full sun. Highly ornamental and compact, it is perfect for rock gardens or dry flower beds. Monarchs visit it, especially for its nectar, but it is used slightly less for egg laying than the previous species.
Others
Less well known, tall milkweed (A. exaltata) grows in light undergrowth and tolerates partial shade. It likes cool to moist soils and is suitable for gardens that do not receive sun all day. Finally, whorled milkweed (A. verticillata), more discreet with its very fine foliage, grows in dry, sandy soils. Small in size, it fits well into compact gardens.
Each species has its place. The most important thing is to choose the milkweed that is suited to the conditions in your garden: dry, moist, sunny, or partial shade—there is a milkweed for every soil type. And no matter which one you choose, each one helps provide monarchs with the resources they need to survive.
Sowing
Sowing seeds is the most economical method, but it requires a little patience. Milkweeds can be started indoors from seed, provided they are cold stratified (30 to 60 days in the refrigerator). Once this treatment is complete, the seeds can be sown in trays under artificial light or on a sunny windowsill. This method produces vigorous young plants that can be transplanted to the garden in May or June.
It is also possible to sow directly outdoors. The simplest method is to sow dormant seeds in the fall: the seeds spend the winter in the ground and germinate naturally in the spring, as they would in nature. You can also sow in the spring, but only after stratifying the seeds in the cold to break their dormancy.
How to Do Dormant Sowing of Milkweeds
Dormant sowing involves sowing the seeds directly outside in the fall so that they spend the winter in the cold and germinate in the spring, as they would in nature. This is the simplest and most reliable method.
- Choose the location: choose a location that meets the needs of the selected milkweed species.
- Prepare the soil: lightly scratch the surface to remove weeds and debris.
- Sow the seeds: scatter them over the entire surface, or in small groups spaced apart. The idea is to prevent the young plants from growing too close together and competing with each other. As a guide, allow about 1 to 2 grams of seeds (150 to 300 seeds) per square meter.
- Cover lightly: add a thin layer of soil or compost ( about 5 mm or 1/4 inch), just enough to protect them from birds and wind.
- Protect if necessary: if you are concerned about drying out or predators, sprinkle a very thin layer of shredded leaves or compost. Avoid thick mulch, which will block germination.
- Let winter do its work: rain, snow, and frost will ensure natural stratification. In the spring, the young shoots will sprout when conditions are favorable.
The ideal time for dormant sowing of milkweed is after the first cool nights of fall, when the temperature drops steadily to around 0 to 5°C, but before the ground freezes for good. Depending on the region, this is usually from mid-September to the end of October, sometimes even until early November in milder areas. The important thing is that the seeds spend the whole winter in the cold without germinating in the fall, so that they can sprout naturally the following spring.
Division
Some species are easily propagated by division. Common milkweed produces long rhizomes that can be removed and replanted in spring or fall. Butterfly weed, which grows in clumps, can be divided in early spring. This quick method produces mature plants that are already well adapted to local conditions and ensures strong regrowth.
Planting Potted Plants
Finally, several milkweeds are available as potted plants in nurseries, including the butterfly weed, which is very ornamental with its orange flowers, and marsh milkweed, which is prized for its large flowering clumps. This approach, which is a little more expensive, guarantees quick results and avoids the uncertainties associated with germination. It is the ideal method for integrating milkweeds into a flower bed and enjoying blooms from the very first season.
Prepare for the Return of Monarchs Now
The monarch is much more than just a butterfly: it is an indicator of ecosystem health, a pollinator, and a symbol of biodiversity. Its migratory cycle, which depends on milkweed in Canada and the United States, nectar-producing flowers along its route, and oyamel pine forests in Mexico, demonstrates how interconnected ecosystems are. Its decline alerts us to habitat loss, pesticide use, and the effects of climate change.
Because it is well known and loved by the general public, it also plays a flagship role: by protecting the monarch, we are also protecting a multitude of other pollinators and the ecosystems on which they depend. It also reminds us that gardeners are not alone: every local action, such as planting milkweed or reducing pesticide use, is part of a collective and international effort to maintain the great migratory route of this iconic butterfly.
As the monarchs leave us, it’s time to prepare for their return: dormant seeding is probably the simplest and most effective way to grow milkweed to support this endangered species. It’s certainly also the most laidback method… and the most natural!
I grew marsh milkweed from seeds. While the plants were still in their pots, monarch caterpillers came and ate all the leaves off the plants. While i’m crazy thrilled, i am wondering if the plants will recover?
I am always amazed that monarchs find my patch of swamp milkweed out here in the country. It is such a beautiful sight.
Thanks for this article! The Monarch is indeed a good barometer of the state of our pollinators. I am delighted when they finally appear (here usually mid summer) and frequent my garden. So far I have only ever seen eggs and caterpillars in my common milkweed (though I have swamp and Tuberosa in the garden as well) so I think that must be their first choice.
I am always encouraging people
In the neighbourhood to plant more milkweed and other native pollinator friendly plants. Alas, many still
have gardens full of sterile ornamental flowers, and I feel bad seeing bees or butterflies flitting hopelessly over these gardens, wasting precious energy. A Monarch here could die of starvation flying over stretches of our city blocks.
Thanks for spreading the word about milkweed.