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How to Grow Swamp Milkweed

These instructions were prepared for Nature NB by the Saint John Naturalists’ Club.

So, you got your free Swamp Milkweed seeds from Nature NB are aren’t sure where to begin! Here’s the tried and true method, tested and described for you by members of Maritime Monarch Watchers and the Saint John Naturalists’ Club. At the bottom of this page, we’ve also included information about other methods we’ve tested if you want to try something new!

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.

A photo of swamp milkweed in bloom.
Swamp Milkweed in bloom. (Photo by Nelson Poirier)

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)

Other Methods for Preparing Swamp Milkweed Seeds


Don’t Have Your Seeds Yet? Order Them Now!

We send out Swamp Milkweed seeds on a pay-what-you-can basis, which means that donations at the time of ordering are encouraged, but not required. All orders, regardless of donation amount, will include one pack of seeds unless otherwise stated.

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