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Growing Milkweed in Ontario

September 10, 2020

By Karin Davidson Taylor, Education Officer, Royal Botanical Gardens.

Milkweeds are dying back now that it’s September and pods are maturing getting ready to ‘pop’ to release their oval seeds attached to fluffy pappus. Over the summer, these plants have played a critical role in the lives of the Monarch butterfly whether it’s the leaves as caterpillar food or flowers as a nectar source for adults.

Monarch eggs on milkweed
monarch caterpiller on milkweed in field

Milkweed Characteristics

Milkweed can be found in every province of Canada, but they have not been found in the northern regions including the territories. There are several types of milkweed and they grow in a variety of habitats from fields to forests to wetlands, but all have that distinct milky latex in all parts of the plant.  Their flowers are a large in round or flat clusters ranging in colour from white to green to pale pink to bright orange. Their pods are all basically the same shape, but some are long and smooth or fuzzy, while others a shorter and with soft spikes, but all contain brown oval seeds attached to fluffy pappus that catches the wind and helps distribute the seeds to new sprouting spots. Some have wide leaves, some have very narrow leaves, some leaves are opposite, some are alternate, and some are whorled. The milky latex contains cardiac glycosides to varying degrees depending on the species. The plant uses the toxin to protect itself from herbivores, but there are some insects, such as the Monarch, that incorporate the toxin and become unpalatable to potential predators.

"Monarch Waystation" sign in Kippax Garden with native plants and milkweed in the background

Many Uses of Milkweed

Monarchs aren’t the only ones that use milkweed; so do other animals and humans, too. The plant fibres from the stem have been stripped off by Northern Orioles to make a nest or the pappus is used to line their nest. Insects use the hollow stems to create egg chambers. Human uses include fibre, food, and medicine. The stem’s fibres are strong and have been used by Indigenous peoples to make ropes and bowstrings. According to William Cullina*, the pappus “is six times more buoyant than cork and five times warmer than wool.” Because of its buoyancy, children were sent out to collect milkweed pods and the pappus was used in WWII for lifejackets. It has great insulative qualities for not only coats, but also cars and ambulances. It absorbs oil but not water so is also a natural and efficient way to deal with oil spills. There was research in the 1940’s to investigate it as an alternative to rubber tree latex, but not successfully. Whether cooked in batter, used to make a syrup or as meat tenderizer, when cooked the toxin is usually denatured, but do your research well before attempting to use it. Lastly its genus name, Asclepias, gives a hint as to one of its other uses — medicinal; Asklepios is the Greek god of medicine. It has been used to treat infections, warts, asthma, and other ailments.

Ontario Species

In Canada, there are 14 different species, one of which, White Milkweed (Asclepias variegata), is extirpated; found in USA, but not Ontario or Canada anymore. There is one Canadian species we don’t have in Ontario — Showy Milkweed (A. speciosa), but it’s the only species found in BC.

If you visit Royal Botanical Gardens, in the Helen M. Kippax Garden you will see four of the twelve species found in Ontario. Many of us are familiar with tall Common Milkweed (Asclepias syriaca) with its sweet-smelling pale purple round umbels of flowers. It prefers sunny locations, tolerates drier conditions and can be found in roadside ditches, fields and more frequently, in gardens. This species is found across Canada and in Ontario as far north as Sioux Lookout and with the changing climate it may move further north. Once considered a noxious weed, it is now a welcome addition to a lot natural and cultivated spaces.

monarch caterpillars on common milkweed

Swamp milkweed (A. incarnata) has bright pink flatter flowers and long, thin leaves. As its name implies, it prefers moister conditions and tends to grow along shorelines.  The last common Ontario species is Butterfly Milkweed (A. tuberosa), a shorter milkweed usually less than a metre tall. It tolerates drier, sunnier conditions and has bright orange flowers. The fourth Ontario milkweed in this garden is Poke Milkweed (A. exaltata). It prefers open woodlands, forest edges, and roadsides. It is tall with white to pale pink flowers that tend to droop. The leaves are oval, opposite, and have wavy edges.  There are eight more types of milkweed in Ontario that live in various habitats including open prairies, rocky or sandy areas, forest edges, and roadsides.

monarch Catterpillar on Swamp milkweed
Swamp Milkweed
monarch on butterfly milkweed with pods
Butterfly Milkweed
Poke Milkweed
Poke Milkweed (image from Michel Tremblay)

Planning for Next Year

There are a variety of ways you can start to grow milkweed, whether it is by seed sown directly into your garden in the fall, started by stratified seeds in early spring ready for transplanting later on, or split the rhizomes and move to other more open areas of your garden.

Milkweed is a perennial, living more than two years and taking three years to flower and produce seed pods. If you have flowering milkweed, take some time to look below the mature plants for shorter first and second year plants. These smaller plants are building their root systems to support flowering in the third year. Don’t forget to leave space between plants so the Monarchs can get to the leaves to lay their eggs. It also helps the plants stay healthy and may help reduce the spread of aphids. If you are interested in diversifying your milkweed in your garden, check out some native plant nurseries to see what they have in stock. No matter what or when you plant, you’ll be supporting Monarchs!

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