Photo: Janet Kempster

Milkweed Seeds are BACK!

Yes, you read that right: we got our hands on another shipment of Swamp Milkweed seeds from the Saint John Naturalists’ Club and the Southern New Brunswick Monarch Watchers. Read on to find out how you can get a free package to plant at home!

What is Swamp Milkweed?

Swamp Milkweed (Asclepias incarnata) is a variety of milkweed that is used in pollinator gardens and landscaping. It can also occur in the wild, but is more uncommon in New Brunswick. Unlike Common Milkweed, the more prevalent wild variant of the plant in this area, Swamp Milkweed does not have a rhyzomatic root system, meaning it won’t spread beyond where it has been planted. Its bright green leaves and vibrant pink blooms make it an attractive addition to any New Brunswick garden.

Milkweed is also the only plant on which the Monarch butterfly can lay its eggs. After hatching, Monarch caterpillars devour the leaves of the plant until they are ready to go into a chrysalis. The blooms of the milkweed plants also serve as sources of pollen and nectar for bees and butterflies in late summer.

Ensuring that there is plenty of milkweed available for Monarchs here in New Brunswick is essential for conservation and survival.

Swamp Milkweed / Asclépiade incarnate

Swamp Milkweed in bloom. (Photo by Helen LeBlanc)

Monarch egg / Oeuf de monarque
Monarch caterpillar / Chenille de monarque
Monarch Butterfly / Papillon monarque

From egg to caterpillar to butterfly, the Monarch relies on milkweed throughout many stages of its life. (Photos by Bev England)

How Do You Harvest Milkweed Seeds?

In late summer to early fall, after Monarch caterpillars have begun to eclose (the term for emerging from a chrysalis), butterflies will load up on nectar to give them energy for the long flight to Mexico. But after they’ve eaten the milkweed leaves as caterpillars and enjoyed the nectar as butterflies, the plants begin to die off as the thermometer dips. The plants will transform, producing hearty pods full to bursting with seeds. Groups like the Southern New Brunswick Monarch Watchers will then harvest these pods, dry them out, and extract the seeds in a tedious process which requires the seeds to be separated from the connected white fluff. This fluff is an adaptive feature which acts like a parachute to allow the seeds to be carried far and wide on the wind, but when harvesting seeds, it can be quite a nuisance. Luckily, the group discovered that using a Shop-Vac is an effective method to do this, and have volunteered their time to prepare seeds for nature lovers in New Brunswick.

Janet Kempster & Jim Wilson
Jim Wilson

From left to right: Janet Kempster and Jim Wilson use a Shop-Vac to separate Milkweed seeds and fluff; a bin of Swamp Milkweed seeds is ready to be bagged; Wilson shows what the isolated fluff looks like. (Photos by Bev England)

How to Grow Swamp Milkweed

Swamp Milkweed seeds need to be vernalised, which is to say that they need an extended period of cold treatment before planting. The best way to give the required vernalisation is through stratification.

To stratify seeds, place them in slightly damp potting soil (sterilized soil is best), sand, or damp paper tower in a plastic bag or container in a cold, dark place for six to eight weeks. A good place is the vegetable drawer of a refrigerator where it’s consistently cool. Do not allow seeds to freeze!

Tip! “Shocking” seeds that have been refrigerated by soaking them in warm water for 24 hours before planting may improve germination rates.

After a vernalisation period of six to eight weeks, the seeds can be planted in warm (70° F / 21° C), moist potting soil in flats or pots, indoors. Germination should take ten to fourteen days if the temperature is maintained.

Once the seedlings have emerged, the soil should be kept moist by watering the flat from the bottom. You can water from the bottom by placing the flat in a sink or larger container with two inches of water until moisture appears on the soil surface. The soil should be kept moist, but some care is needed to keep the seedlings from getting too wet.

Plants can be transplanted when they are three to six inches in height. Before transplanting, acclimate them to outdoor conditions for a few days by placing them in a sheltered location during the day and then bringing them indoors at night. Seedlings should be planted 18-24 inches apart and newly transplanted plants should be watered frequently. Add mulch around the seedlings soon after planting.

Milkweed Seedlings / Semis d'asclépiade

Swamp Milkweed seedlings ready to be transplanted. (Photo by Bev England)

How to Grow Swamp Milkweed at Home

Using and Updating iNaturalist

Once summer arrives, your milkweed seedlings should be on their way to becoming well-established plants. They may even be attracting Monarch butterflies! What’s your next step?

Check out iNaturalist, a website and mobile app that allows users to log the species in their areas. As one of the largest citizen science platforms in the world, the information that you upload could one day be used by researchers for conservation work!

Head to inaturalist.org or download the free app through your phone’s app store. Once your account is set up, all you need to do is take photos of the species you find, upload them to the site or through the app with some basic information, and wait for other members of the community to confirm your identifications. Spend the summer logging your Swamp Milkweed and posting updates about any winged friends that stop by to enjoy the nectar or lay their eggs.


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