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Perennial Milkweeds for Your Pollinator Garden

We’ve lamented the difficulty of finding perennial milkweed species (Asclepias) before (read more here). They tend to be difficult to find in substantial quantities, slow to germinate from seed, and resentful of commercial growing conditions–rich soil, constant irrigation and a pot? No, thank you.

Asclepias incarnata 'Iceberg' shows off clear white flowers. Image courtesy Stuifbergen Bloombollen.
Asclepias incarnata ‘Iceberg’ shows off clear white flowers. Image courtesy Stuifbergen Bloombollen.

There are, however, exceptions. As we at NHG strive to help you, the gardener, in your quest to support the Monarchs, we’re working with growers on all fronts to get a more consistent supply of perennial species in addition to the Mexican or tropical milkweed, Asclepias curassavica. Here are two to try that recently arrived:

‘Swamp milkweed,’ Asclepias incarnata, is a north American native species that actually thrives in damp conditions. It’s a robust grower when it’s happy; a single plant can reach 4′ tall and nearly as wide in one season. We have a cultivar of this native plant (for which we often borrow the term ‘nativar’) called ‘Iceberg’; its flowers are a clear, fresh white as opposed to the oranges and pinks that are common in the wild. With plenty of moisture, it’s happiest in full sun, where it produces abundant nectar that supports a variety of pollinators. Swamp milkweed is considered a great attractant for Monarch butterflies, and the caterpillars can devour a large mass of it in a surprisingly short period of time–but it tends to spring back easily. As with all milkweed, its milky sap contains toxic compounds that make it poisonous–and distasteful to other insects.

Common ‘Butterfly Weed,’ Asclepias tuberosa, is another north American native perennial species we’re expecting more of this week. While it’s easier to propagate from seed (in fact, once established, it will often self-sow in the landscape) it’s very slow to establish, often taking 2-3 years before blooming. Additionally, it produces a thick taproot that is difficult to transplant, making commercial cultivation a bigger challenge. It’s quite drought tolerant and will be quite happy in a sunny location poor soil, but some amending to ensure good drainage and air circulation can help it establish more quickly. It grows to about 2′ x 2′ and produces clusters of bright, tangerine-orange flowers in the wild; and like its cousins, is a favorite of Monarch butterflies.

Variegated 'Monarch Promise' tropical milkweed. Image courtesy Hort Couture.
Variegated ‘Monarch Promise’ tropical milkweed. Image courtesy Hort Couture.

If you grow or have grown the Mexican milkweed, A. curassavica, and want to try something unique, check out the new-this-year hybrid ‘Monarch Promise’ that’s caused quite a stir. Smaller in stature than regular tropical milkweed, it displays the same vibrant flowers with delicately blended, pink-and-white variegated foliage. While  it’s not reliably perennial in our growing area, it’s a lovely new addition suitable for containers and sunny border spots in the garden.

Please note that inventory can change rapidly during spring, and while supplies are limited, we hope to receive weekly successive crops and to continue to work with growers source other perennial milkweed species. In the meantime, happy butterfly gardening!

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