Swamp Milkweed Plants that Grow In Water

Can swamp milkweed be grown in pots submerged in water?

Swamp milkweed is a native milkweed species that loves to grow in wet habitats like ponds or rain gardens. But can you grow it in a pot that’s sitting under water in your yard pond or water feature? The answer is yes, you can! This moist-loving milkweed will be happy in a container fully submerged under water.

• What is Swamp Milkweed?
• Do I need soil to plant milkweed in water?
• How much sun does swamp milkweed require?
• Should I fertilize milkweed plants in water?
• Does fertilizer hurt or kill monarch caterpillars?
• Caring for Swamp Milkweed
• Can I plant other milkweed species under water?

What is Swamp Milkweed?

Asclepias incarnata (swamp milkweed) is a native milkweed for monarch caterpillars and a nectar source for butterflies that boasts beautiful pink flowers. Native plants should be a cornerstone for any gardener seeking to attract pollinators and properly support them. For more photos and information on this milkweed species, check out our swamp milkweed plant page

Do I need soil to plant milkweed in water?

If you use soil in your milkweed container be sure to find a soil suited for aquatic planting. Otherwise, it will float to the surface and and muddy the water. Use a top layer of pond rocks or gravel to keep soil in place. 

For our milkweed experiment, we did not use soil and just planted inside a pot filled with small pond rocks and gravel

How deep should I place the milkweed container?

The top of the pot should be 1 to 2 feet under water. Mature swamp milkweed typically grows up to 5 feet tall

How much sun does swamp milkweed require?

Ours is in a sunny area where it gets a good 6 to 8 hours a day. Early in the season this seems like a good option for growing milkweed under water. At this point we’re not sure if our perennial plant will bloom to attract monarch butterflies, bees, hummingbirds, and other beneficial wildlife in pollinator gardens. A second-year Asclepias incarnata with multiple stalks should bloom and we’ll update this article with photos and info later this summer.

Should I fertilize milkweed plants in water?

For this experiment, we have not fertilized, but many experts recommend using fertilizer for aquatic plants. 

For established perennials in our yard/garden, we use a slow release fertilizer which helps milkweed plants thrive, in our experience. For annuals and first year perennials, we use Miracle-Gro water soluble fertilizer (half the recommended amount) to make sure new plants don’t get stressed from absorbing nutrients too quickly.

Does fertilizer hurt or kill caterpillars?

Over the years we have tried many types of fertilizers both organic and non and have seen zero evidence that they’re negatively impacting caterpillar development or hurting our steady stream of pollinators. We have often used fertilized leaf or stem cuttings (from the garden) to feed caterpillars in our porch and they have continued to thrive.

Caring for Swamp Milkweed

Pull your plant out of the pond in early spring to see if your plant survived and to see if its outgrown the current container. We started with a 10″ pot and were still using this in year 2. By the end of the second season:

Can I plant other milkweed species under water?

We have not tried other milkweeds, but Asclepias perennis (aquatic milkweed) is another milkweed species that prefers wet soils, so it might be a good option for a milkweed experiment. 

Do you have questions or comments about swamp milkweed plants that grow in water, or have you tried this in your garden? Post a comment or question in the comment box below