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Rick’s Native Plant of the Month | Milkweed

May 12, 2023

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Bridge Gardens

Our native milkweeds are important plants for native pollinators and other insects.

They provide food in the form of nectar and pollen with their flowers and succulent leaves for the larval stages of butterflies, including endangered monarchs. They are deer-resistant, easy to grow from seed if given a cold period, difficult to transplant, once established, because of deep taproots.

Milkweeds grow around the world, mostly in the tropics of Africa and South America, but some species also grow in the temperate regions of North America. They are so named because of their milky sap, which is poisonous to humans and many animals, but the preferred food for monarch butterfly caterpillars, as well as some beetles and moths also immune to the sap’s noxious chemicals.

Generally, milkweeds are rather coarse plants, but their flowers are quite beautiful and, if you look closely, rival those of orchids in complexity. Fruits are characteristically pods, filled with seeds arranged in rows and topped with clusters of white, silky hairs. When ripe, pods split open and seeds are carried everywhere on the wind.

In the past, milkweeds were grown commercially to harvest these silky hairs, known as floss. Milkweed floss was used for thermal and acoustic insulation and as stuffing for pillows and winter coats.

The following are species native to eastern North America, including Long Island

Common milkweed (Asclepias syriaca)

This plant has received lots of attention recently because it is the preferred food of monarch butterfly larvae and crucial for its survival. Though monarchs lay eggs on all our native milkweeds, they prefer the leaves of common milkweed as food for caterpillars and as shelter for chrysalises.

Though important for the monarch, common milkweed is hardly a garden-worthy plant in the traditional sense. Coarse, weedy, spreading aggressively by seed and underground roots, it easily forms large, unstoppable colonies and is often a target for eradication by farmers.

Common milkweed flowers are pink, fragrant and long-blooming. Though too vigorous for most gardens and borders, it is a great plant for naturalizing, especially in sites with poor, dry soil. If you have a corner of your property that you no longer want to mow, consider planting this milkweed to fill in the space and create a food source and breeding ground for pollinators.

Almost identical in all respects to common milkweed, purple milkweed (A. purpurascens) has attractive, deep magenta flowers all summer. Slightly less invasive is green milkweed (A. viridis), named for its green and purple flowers.

Swamp milkweed (A. incarnata)

Even though this species is commonly found in swamps and damp meadows and along pond edges, swamp milkweed also grows easily in average, well-drained soils. With pink, white or mauve summer flowers atop 3-4-foot leafy stems, it is perhaps the most garden- and border-worthy of the milkweeds. It spreads easily from seed, but not from underground roots, so it is easy to control by weeding.

Swamp milkweed pairs well with native grasses and is great for rain gardens and naturalizing in sunny meadows.

Butterfly weed (A. tuberosa)

This milkweed grows best in full sun and sandy, dry, infertile soils. Where happy, it will spread by seed, but often, plants succumb to midsummer’s heat and humidity, especially in the moist, fertile soils we have at Bridge Gardens.

Perhaps the showiest of our native species, butterfly weed is admired for its long-blooming clusters of yellow and orange flowers that appear throughout summer. Butterfly weed is also one of the shortest milkweeds, usually growing 12-18 inches tall. Unlike other species, it does not have milky sap.

Plant butterfly weed in rock gardens, dry meadows and parking lot islands and along road edges.

Whorled milkweed (A. verticillata)

One of the few milkweeds that tolerate partial shade and moist soils, whorled milkweed is also well-adapted to infertile, dry sites in full sun. It is found naturally in dry meadows, open woods, pastures and along roadsides.

Summer brings clusters of small, greenish-white flowers to the tops of this milkweed’s 2-3-foot stems, which are covered with whorls of narrow, needle-like leaves. A great candidate for naturalizing, whorled milkweed will self-sow, but is not as weedy as other milkweeds.

Poke milkweed (A. exaltata)

Poke milkweed is another species that grows readily in partial shade, preferring moist woods and woodland edges. It has attractive, drooping clusters of green and white flowers on 3-4-foot stems.