Swamp Milkweed

Swamp Milkweed

Asclepias incarnata


A wet-loving perennial, swamp milkweed is the daintier native cousin of the more familiar common milkweed that grows throughout Ontario. It is a tall wildflower, sometimes growing over a meter in height. The stems grow from a compact white fibrous root system with more stems emerging each year. It has oppositely arranged smooth leaves that are pointed at the tip and rounded near the petiole. The pink and white flowers emerge in early August with a vanilla-like scent. Milkweed gets its name from the bitter milky sap it bleeds when torn or broken.


Swamp milkweed thrives with full sun and wet soils. Naturally found in marshes, swamps and other open wet sites. It has become an incredibly rare plant on PEI, occurring naturally on a handful of properties.


Milkweed is very easy to propagate. Wait for the a few pods to start to open, then check to make sure the seeds are quite brown. They should not be dried out, but also shouldn’t be showing any green. The seeds are attached to long, fluffy fibres. The easiest way to clean the seed is to leave them in the pod. Pull on the fibres at the outer end of the seeds and you’ll come away with the fibres in one hand and the clean seeds in the pod in your other hand. If you initially take the seeds out of the pod and then try to clean them, it is quite a task if you are doing any amount.

Seeds should go into the ground as soon as possible. Plant seeds every 2 inches (5 cm), in rows 4 inches (10 cm) apart, at a depth of 1/4 inch (6 mm). Cover thinly with mulch. Germination will be quite high in the spring.

Wildlife Uses:

An incredible wildlife plant, swamp milkweed is a crucial food source for Monarch butterflies. It also attracts a dizzying number of pollinators from wasps to bees to flies and much more. It is a standard in all pollinator gardens, since it is both useful and beautiful.

Areas of Usage:

Don’t let swamp milkweed’s rarity fool you into thinking this isn’t an amazingly adaptable and tough plant. With some thoughtful care, our native milkweed can thrive in an incredible variety of sites. Like all wetland plants, it will tolerate wind on wetter sites but needs shelter if things are dryer. Proper mulching and the addition of organic matter go a long way in ensuring the health of your milkweed. They also self-seed, so planting a few will have far-reaching results in just a few years. They are also excellent plants for open riparian zone and marshland restoration.

Additional Information:

Milkweeds and Monarchs make an incredible duo. Monarchs have adapted over time to rely on milkweed for food, egg laying sites, even processing the milky sap into a defence mechanism. We’ve grown milkweed at Macphail Woods since 2012 and each year more and more Monarchs come. That being said, it is always risky to put all your eggs on one plant and the rarity of swamp milkweed on PEI is yet another challenge for the hard-pressed Monarchs. Luckily, it is a tough and vigorous species and a prolific seeder. Local community-driven efforts are starting to restore this beautiful species’ population across the province.

Milkweed has seen a number of commercial uses over the years too. The fluff attached to their seeds is both an excellent insulator and quite bouyant. During World War II, it was used as stuffing in flight suits and life jackets, and plantations were grown in the United States to supply the Air Force. Today, several companies are using milkweed fluff to replace, or to add to, goose down in their high-end outer-wear jackets.

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