Common Milkweed Host Monarch Butterflies

Milkweed, of which there are about 14 different types in Canada, is the only host plant for monarch butterflies. In summer, the female monarch feeds on the nectar and lays eggs on the underside of young leaves. Once the larvae emerge, they feed on the leaves, creating an arc-shaped hole. Several weeks later, after the caterpillar has eaten 20-30 leaves, it goes on to find a more suitable spot to become a chrysalis. Given favourable weather conditions, the life cycle can be completed within 25 days.

More than 90% of monarchs have disappeared over the last few decades. You can be a beneficial partner in their restoration by introducing milkweed into your garden. The flowers are a great source of nectar for butterflies, hummingbirds, bees, and other beneficial insects. Once found in abundance in nearly every farm field, ditch, and disturbed site, common milkweed numbers have been in dramatic decline in recent years, due in part to suburban development and the increased efficiency of herbicides.

Quick Growing Guide

Botanical Name: Asclepias syriaca

Botanical Family: Apocynaceae

En français: Asclépiade commune

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Water: Sparingly

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Common Milkweed is prized for its dome clusters of sweetly-scented, pinkish-purple, starry flowers, which bloom from early to late summer. The colourful blooms give way to prominent seed pods in the fall, which look great in dried flower arrangements. When the seed pods open, they reveal seeds with long, silvery-white, silky hairs. The stems are clad with thick, large, oval leaves.

This is one of the easiest and fastest to establish of the milkweeds. A great choice for the flower garden and for natural settings.

Where to Plant

The Common Milkweed wants a sunny location. It looks beautiful in an informal border or in a large open meadow. You’ll want to plant several as those hungry caterpillars could outstrip your single plant. In fact, you may consider choosing other varieties with different bloom times to help extend the stay of visiting monarchs. 

As this is an aggressive plant, consider planting other likewise plants close by to keep it in check. Goldenrod, mint, blazing star, evening primrose are only a few examples of the many you might consider.

Caring for Asclepias syriaca

The plant has a medium growth rate and develops a large root system which doesn’t like being disturbed. It’s happy with a light watering from time to time and never needs to be fertilized. If in July you choose to clean up its appearance, begin by checking the underside of the leaves for any possible eggs or larvae. You can then cut it back to about half its size. Doing so promotes the addition of new growth that will continue to support the monarchs into the fall. Fall is also a good time to annually remove seed pods before they open and self-seed. Should you choose, you could also mow your milkweed bed.

How to Transplant

The common milkweed has an extensive root system of both a long tap root and rhizome roots. The best time to transplant would be in cooler spring weather or in the fall when the plant is done blooming and producing seeds. The rhizome roots cause the plant to spread, so choose a smaller plant that is about 12” away from a larger section.

Consider wearing gloves to protect your hands from the toxic sap as you will be digging up about 3” – 6” of the root around the selected plant. Place this new plant into a container covering the root about 2” deep in medium soil. Clip the plant, leaving only one set of leaves. Position the container in a location that gets a minimum of 2 hours sun and keep the soil moist. Several weeks later the plant can be moved to its new bed. Be sure to offer it lots of water until established. Afterwards it will be happy with soil that is on the dryer side.

Propagating Cuttings

Taking cuttings mid-summer will allow for the 6-10 weeks needed before fall transplanting occurs. Soil based mediums have oxygen levels too low to sustain milkweed rooting. A standard cutting mix of 80/20 perlite to peat can be used or a 50/50 mix of sand to perlite, peat or vermiculite also works well. Cut a 4” (10 cm) long stem that has 3-5 leaves. Scrape the bottom third of the cutting with a sharp knife and apply rooting hormone.

For best results, place the cutting in its own mini greenhouse made from a 2L soda bottle. If using a standard container make sure to spray the soil and leaves daily. Leave your cutting in a protected shady area until ready to plant in the sun.

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