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Garden Obstacles: Picking the Right Milkweed

Updated: Dec 30, 2022

I know it sounds weird calling milkweed a garden obstacle but many of you come to me looking for Asclepias syriaca (Common Milkweed) because you were told it is the best host plant for the Monarchs. While this may be true, it is also an aggressive garden thug. Nobody tells you this when you buy it, but I do. It is great in a meadow, along the roadside, or in a garden that is left alone to naturalize. So, if you have the space, you should plant common milkweed. If you do not have the space or are one to get upset when something grows a little out of hand, there many other milkweeds to choose from and they are all native to Long Island.

Several varieties grow in clumps instead of running. They all self-sow readily in the garden. If you want to control this, tie a string or put a rubber band around the seed pods. This will prevent them from going everywhere once they split open. You can save the seeds to share with friends or you can put them in different areas of the yard.

Please note: ALL milkweed contains cardiac glycosides and resinoids making them poisonous. It is toxic in large quantities only. The Monarch caterpillar ingests the milky sap and after the second instar, it becomes poisonous to predators.

I'll start with Common Milkweed and the other milkweed options will follow.

Asclepias syriaca - Common Milkweed

Needs full sun and grows 3-5' tall but may reach 8' tall in ideal conditions. The fragrant flowers may be white, pink, lavender, or purple and have a long bloom time of June through August. This makes it a superb nectar source for butterflies and bees. Native Americans use the fluffy floss as a fiber source. During WWII, it was used to make life jackets. Today it is farmed by people realizing its use in jackets, pillows, and comforters. Some like to plant it in a large container, but it will get out through the holes in the bottom and by seed. It is also the host plant for the Milkweed Tussock Moth. It spreads by rhizomes and seeds to form small to large colonies. Usually deer resistant.

Photos: Pink flower (Lucy Bradley, CC0), White flower (Douglas Goldman, USDA, CC BY-NC 4.0), Form with flower (Douglas Goldman, USDA, CC BY-NC 4.0), Spent seed pods (KMS Native Plants)

Asclepias exaltata - Poke Milkweed

This is a fun, slow-growing milkweed as it prefers partial shade (woodland edge). Tolerates full sun but the leaves will not get big. It does prefer rich, moist soil. Growing 2-6' tall and sometimes taller by 12-24" wide, it has been known to hybridize with Common Milkweed. The fragrant blooms from July through August attract a large number of native pollinators. Deer resistant but rabbits may nibble on it. The common name of Poke Milkweed comes from the look of the leaves as they resemble our native Pokeweed.

Photos: Flower (Steven Daniel), Form (Jacqueline Donnelly)

Asclepias incarnata ssp incarnata - Swamp Milkweed

This lovely milkweed grows 36-60" tall by 2-3' wide when mature. It does not run in the garden, as it is a clump grower, making it perfect for a mixed border or pond plant. Don't be thrown off by the common name of swamp milkweed as it will grow in average garden soil and tolerate a good amount of drought. Prefers full sun to partial shade. It is a another long bloomer starting in July and going through to September. If a mauve pink isn't your thing, it also comes in white. 'Ice Ballet' brings just as many polliantors in as the straight species. It is a nectar source for butterflies, bees, wasps and hummingbirds.

Photos (KMS Native Plants): Eastern Tiger Swallowtail nectaring on flower, Carpenter Bee nectaring on flower, Milkweed bug, White cultivar called 'Ice Ballet'

Asclepias incarnata ssp pulchra - Eastern Swamp Milkweed

This is one of my favorites for the garden! Just like the Swamp Milkweed above it is a clump grower and not a runner. The leaves are a bit different with a kind of hairy feel to them. The above milkweed has shinier leaves. Prefers full sun to partial shade and grows 3-5' tall and 2-3' wide in average to wet soil. Tolerates a bit of drought.Blooms July to September. A great nectar source for butterflies, bees, wasps, and hummingbirds.

Photos (KMS Native Plants): foliage, flower, Monarch butterfly, open seed po