Native Milkweed for Ontario Gardens

Milkweeds admittingly have an image problem (having "weed" in their common name doesn't help!) and are often seen as thugs or weeds. This is completely unfair as many milkweed species are well-behaved enough for a garden setting and have a lot of beauty and wildlife value to add to our gardens. Wildlife gardeners have a variety of milkweed species to choose from in Ontario and there is a Milkweed for almost any growing condition in your garden.

In this article, we will discuss the benefits of growing milkweed in your garden, their relationship with Monarch Butterflies and introduce our perspective on managing aphids on milkweed plants.

Click here to jump right to the list of milkweeds.

Benefits of Milkweed in Your Garden

• Host Plants

Milkweeds are well known as the only host plants for caterpillars of the Monarch butterfly, however they are not the only insects to feed on it! Red Milkweed bugs and Milkweed Tussock Moth caterpillars also feed on parts of Milkweed. Like the Monarch caterpillars, these species have evolved to eat and accumulate milkweed toxins in their bodies thus making them less appetizing to predators. While they have big appetites, they should not be seen as pests or competition for Monarch caterpillars. They have all evolved alongside each other and are part of a healthy, functional ecosystem.

• Floral Resources

Milkweed flowers are rich in nectar and pollen and therefore support a wide diversity of insects including Carpenter bees, Bumblebees, Leafcutter bees, butterflies, moths and even Hoverflies. In fact, even the Ruby-Throated Hummingbird will drink nectar from the flowers. Once you get up close with a Milkweed patch in bloom, you will be amazed by the diversity of life that it supports. In our experience, all milkweed species provide equally valuable floral resources.

• Diversity

Ontario has a variety of different Milkweed species, with adaptations to different conditions. Swamp Milkweed for rain gardens, Butterfly Milkweed for sunny, dry gardens and even Poke Milkweed for dry shade gardens. There really is a milkweed for every garden!

• Nesting Material

Milkweed naturally produces nesting material for birds. They will use the familiar white fluff from seedpods and fibers from the stems to build their nests.

• Fragrant Flowers

Milkweed flowers are some of the most fragrant native plants in Ontario. Common Milkweed is by far the most fragrant with Swamp Milkweed coming in second. They give off a florally-vanilla smell that drifts through the garden on windy days.

Milkweed for Monarchs

We can’t talk about milkweeds without talking about Monarch butterflies! Milkweeds are well-known as the only host plants for their caterpillars who are dependent on them to complete their lifecycles.

The reason that they are so specialized on milkweed is that they have evolved the physical and chemical adaptations to eat Milkweed when many other insects can’t. Before eating, caterpillars will often sever the mid-rib in a leaf, therefore cutting off the main flow of sticky white sap.

This allows them to much away without their mouth parts getting stuck together from too much sap. In addition, their bodies will accumulate toxins from the Milkweed plants, thus making them less appetizing to predators.

These adaptations allow them to eat a plant that is mostly untouched by other insects who haven’t evolved to eat it, thus reducing their competition for food. Unfortunately, this specialized diet comes with a downside - no milkweed means no Monarchs!

Monarch butterflies are also special when it comes to their winter survival techniques. While many butterflies will over-winter in our gardens as larvae or adults, Monarchs use environmental cues to signal them to fly south, sometimes as far as 5000km to over-wintering grounds in Mexico! They are the only butterfly known to make a two-way migration as birds do.

Unfortunately, Monarch Butterfly populations have been declining over the years. This is largely due to a lack of habitat.

But this is where your garden comes in! You can support Monarch butterflies, and a whole host of other wildlife, by planting milkweed in your garden. Doing so will help weave your garden back into natures web of life.

The Best Milkweeds for Ontario Gardens

We will be focusing on Milkweeds that are best suited to a garden setting and also commercially available.

• Poke Milkweed (Asclepias exaltata)

• Swamp Milkweed (Asclepias incarnata)

• Purple Milkweed (Asclepias purpurascens)

• Common Milkweed (Asclepias syriaca)

• Butterfly Milkweed (Asclepias tuberosa)

• Whorled Milkweed (Asclepias verticillata)

Poke Milkweed (Asclepias exaltata)

Exposure: Part shade, shade

Height: 1.5m, 5ft

Blooms: White, summer

Soil: Sand, loam. Prefers rich soil.

Moisture: Average to dry

Poke Milkweed is unique because where most Milkweeds need lots of sun, this one thrives in the shady conditions of forest floors and forest edges. It will even tolerate dry shade if there is a decent amount of organic matter in the soil.

Uncommon in Ontario but can still be found in healthy, deciduous forests.

The large, oval leaves and tall stature of Poke Milkweed make it an excellent structural plant in shady gardens. In summer, droopy clusters of white flowers are presented along it’s slender stalks. The flower clusters are reminiscent of Common Milkweeds but are more sparse.

This Milkweed is not an aggressive spreader and is suitable for shade gardens, pollinator gardens and naturalization.

Pair Poke Milkweed with Bluestem Goldenrod, Pennsylvania Sedge, Large-leaf Aster or Maidenhair Fern.

Swamp Milkweed (Asclepias incarnata)

Exposure: Sun to part sun

Height: 1.5m, 5ft

Blooms: Pink, summer

Soil: Sand, loam, clay

Moisture: Wet to average

Swamp Milkweed, known as bagizowin by the Anishinaabe, is a common species in Ontario, usually found in wetlands, wet roadsides, floodplains and wet meadows. It has an upright stature and slender leaves.

Despite its affinity for moist areas, it is fairly drought tolerant once established in a garden setting. In general, it is a very easy to grow native plant as long as the soil doesn’t dry out completely. It is also referred to as Pink Milkweed because of the cheery pink flowers that bloom profusely on top of the plant.

It may self-seed into gaps in your garden, but individual plants maintain a clumping form.

Swamp Milkweed is one of the more fragrant Milkweeds, with a florally-vanilla smell that drifts through the garden.

Monarch caterpillars often favor this Milkweed (at least in my experience), possibly due to the fact that it’s leaves are more tender and it doesn’t have quite as much white sap. It grows quite tall and maintains it’s structure well into the winter moths to provide winter garden interest.

Good companion plants include Turtlehead, Blue Vervain, Swamp Aster and Spotted Joe-pye. Swamp Milkweed is a great candidate for raingardens.

Purple Milkweed (Asclepias purpurascens)

Exposure: Sun to part sun

Height: 90cm, 3ft

Blooms: Purple, mid-summer

Soil: Sand, loam. Does well in poor soils.

Moisture: Seasonally wet, average, dry. Well-drained.

Purple Milkweed looks similar to Common Milkweed but the flowers are a rich purple colour. The blooms are found at the end of the stems and are more upright than those of Common Milkweeds which tend to flop.

Purple Milkweed is valued in gardens for its rich purple blooms and less-aggressive growth habits. That being said, you will still want to give it some space to spread! In optimal conditions it will spread by rhizomes and to a lesser extend, seeds.

Useful in pollinator gardens, naturalization and meadow gardens.

Good companions include Woodland Sunflower, Pale Coneflower, Big Bluestem or Bergamot.

Common Milkweed (Asclepias syriaca)

Exposure: Sun to part shade (may not flower in part shade)

Height: 1.5m, 5ft

Blooms: Pink/white, summer

Soil: Sand, loam, clay

Moisture: Average to dry

Common Milkweed, known as ninwanzh by the Anishinaabe, is the Milkweed that most people are familiar with as it is readily found in meadows, roadsides, prairies and forest edges.

Common Milkweed sports showy clusters of light pink to white blooms in mid-summer. There is a lot of variability in flower colour between individuals. In my opinion, this is the most fragrant Milkweed with a noticeable florally-vanilla scent that fills the garden.

It may not be suitable for small gardens as it spreads prolifically by rhizomes. It’s best suited to larger gardens or naturalizations. If you really want it in your garden then you can manage it’s spread by removing seed pods and digging up unwanted plants.

Another method for controlling it’s spread is to plant it in part shade. It will grow much slower and shorter but may not produce flowers.

Common Milkweed is very popular with Monarch caterpillars but they seem to favor the young leaves.

Pair Common Milkweed with species that it won’t out-compete such as Woodland Sunflower, Bergamot, Indian Grass or New England Aster.

Butterfly Milkweed (Asclepias tuberosa)

Exposure: Sun

Height: 90cm, 3ft

Blooms: Orange, summer

Soil: Sand, loam, clay. Must be well drained

Moisture: Dry, average.

Butterfly Milkweed is one of the shorter milkweed species and is usually found in prairies, meadows and other dry open areas. It is very well-behaved in gardens.

The deep thick taproot of Butterfly Milkweed makes it one of the most drought tolerant native plants we have. It is easy to grow and adaptable to most gardens and soil types, however, the soil must be well-draining or else the root will rot (this is the most common reason why your Butterfly Milkweed won’t come back up next year).

This deep taproot makes it hard to transplant so choose it’s location wisely!

This milkweed maintains a clumping, bushy form and is very well-behaved with occasional self-seeding. It maintains it’s form well into winter, thus giving your garden winter interest.

The slightly hairy leaves mean Monarch caterpillars tend to favor other Milkweed species. Despite this, it’s still a valuable host plant for Monarchs.

Companion plants include other prairie species such as Nodding Onion, Little Bluestem, Dense Blazing Star, Black-eyed Susans or New Jersey Tea.

Whorled Milkweed (Asclepias verticillata)

Exposure: Sun

Height: 90cm, 3ft

Blooms: White, summer

Soil: Sand, loam, clay, gravelly. Well-drained.

Moisture: Dry

Whorled Milkweed is the shortest plant on this list, rarely topping 3ft. It is usually found in prairies, meadows and open woodlands and is perfectly suited to gardens.

The small, narrow leaves are found in whorls along the solitary stem. Fragrant white flowers bloom in mid-summer into fall and support are especially attractive to beneficial predatory insects.

Whorled Milkweed does well in infertile soils where competition from taller plants is reduced. It can spread to form colonies, but not aggressively.

Companions include Cylindrical Blazing Star, Sideoats Grama, Purple Prairie Clover or even Butterfly Milkweed!

Milkweed Growing Tips:

• Milkweeds can be slow to come up in the spring because the prefer warmer weather. So, be patient. Your milkweeds are very hardy plants if planted in the right location and will come up on their own time.

• Monarch and Milkweed Tussock Moth caterpillars will often defoliate a milkweed but this is nothing to be concerned about. Milkweeds have adapted to constant herbivory from insects and established milkweed plants will easily rebound from hungry caterpillars!

• I recommend planting at least one patch of Milkweed at the front of your garden where you can get up close with them to observe the caterpillars.

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