Plant Swamp Milkweed Seeds for Monarchs

Asclepias incarnata is well known as Swamp milkweed and is one of the milkweeds that are usually highly preferred by the Monarch butterflies. Other common names include Rose Milkweed, Rose Milkflower, or Swamp Silkseed.  Adult female Monarchs will readily lay their eggs on this plant. Queen butterflies may also use Swamp milkweed as a host plant.

As well as being a host plant, Asclepias incarnata is also a great nectar source and attracts many other kinds of butterflies.

Swamp Milkweed Overview

Asclepias incarnata is a native perennial milkweed to the most of the US and Eastern Canada and is hardy from USDA zones 3 to 8. Only the far western states of the US fall outside of the native region.

This milkweed has fragrant clusters of small flowers that are loved by many butterfly species besides just the Monarchs. Swamp milkweed will flower the first summer from seed and like many milkweeds will flower all summer.

Unlike some other milkweeds (such as Common milkweed and Showy milkweed), Swamp milkweed is well behaved in the garden and will grow in clumps rather than invasively spreading around with far-reaching underground rhizomes. It is a common addition to butterfly gardens as it is useful and pretty at the same time.

Swamp milkweed can vary greatly in height anywhere from 2-6 ft but is probably most commonly seen around 3-4 ft tall. They will die back in the fall to return from the ground in the spring.

Another great thing about Swamp milkweed is that like many of the milkweeds it is very attractive to many species of butterflies as a nectar source. So not only will it draw the Monarchs for nectar and hosting, it is a general butterfly magnet.

How to Grow Asclepias Incarnata

As its name suggests, Swamp milkweed is most often found growing in rich moist areas like marshes or near streams in its native setting. It is tolerant of wet clay soils and areas without good drainage.

However, once established it will do quite well in average gardens. Keep it well watered until it is established then water it as you would for any of your plants that require average-moist garden conditions. Some people actually report that it will tolerate dry conditions. However, for hot and dry conditions you may want to consider other Milkweeds such as Butterfly Weed.

Swamp milkweed will grow in full sun or part shade.

Germinating Swamp Milkweed Seeds

Like most milkweeds, Swamp milkweed is most commonly grown from seed rather than cuttings. Asclepias incarnata requires at least 30 days of cold stratification before it will germinate. Cold stratification is the process of exposing the seed to cold and moist conditions to break dormancy.

You can allow nature to cold stratify the seeds for you by planting them outdoors in the Fall or using winter-sowing techniques. Or you can cold-stratify indoors by placing the seeds in moist sand, moist vermiculite, moist coffee filter, etc, in a resealable plastic bag in the refrigerator.  There is a lot of information online about cold-stratification if you would like to research it further.

When sowing Swamp Milkweed seeds, barely cover the seed with soil and keep the soil moist and in bright light because light can help with germination. The seeds should germinate within 1-3 weeks.

Swamp milkweed produces plenty of seed for you to share or start new plants. Collect the seed in late summer/fall just as the elongated seed pod is starting to split open but before the white “fluff” starts to float out. At this stage it is pretty easy to strip the seeds off the white silky threads that will soon fluff up and allow the seed to float off in the wind.

Consider Buying Asclepias incarnata Seeds and Plants

Swamp milkweed is one of the Monarchs favorite milkweeds and is treasured by many butterfly gardeners as a Monarch butterfly host plant due to its beauty, fragrance, attractiveness to many butterflies and “good behavior” in the garden (not invasive). We have other Milkweeds you may want to consider as well. Also, we have an article about raising Monarchs if you would like more information about the Monarch butterfly.