Plant of the Week: Purple milkweed

Many plants depend on wildlife for their reproduction. Insects and birds are major collaborators with wildflowers, as they disperse pollens and seeds in exchange for food and shelter that the plants provide. Generally, plants that are native to a region work best to support the local insects and birds of the region. From spring to fall, these natives attract bees and butterflies, showing us a glimpse of symbiotic relationships that occur in nature.

Photo by Ayinde Listhrop

Approximately 30% of plants on the High Line are native to Northeastern United States. Among them, purple milkweed, Asclepias purpurascens, is one of the go-to plants on the High Line to spot insects throughout the season. From late spring to early summer, the deep rose pink flower attracts long-tongued bees, skippers and butterflies: swallowtails, fritillaries, American painted lady, red admiral, and many others. Purple milkweed may not be a great food source for caterpillars (larvae), because the plant doesn't produce as much foliage as other milkweeds do. Nevertheless, many caterpillars feed on its leaves. Monarch butterfly may be the most well-known that uses purple milkweed as the host plant for its larvae.

Currently at the High Line, visitors can see one of the distinctive features of purple milkweed: seed pods. The seed pod is approximately 5 inches long, smooth and upright, and contains numerous seeds with large tufts of silky hair for wind dispersal. The seed pods are often covered by a swarm of large milkweed bugs feeding on the seeds.

Photo by Ayinde Listhrop

USDA lists purple milkweed as endangered in Massachusetts and Wisconsin, and as a species of special concern in Tennessee and Connecticut. It is also reported that it's rare to find purple milkweed in prolific fertile condition. Apparently, with abundant seed pods, the High Line is an exception.

PLANTING TIP:
Plant Asclepias purpurascens in well-drained soil with dry to medium moisture, in full sun to part sun. It is drought tolerant but immature plants are inclined to wilt and should be watered. It will self-seed in the garden if seed pods are not removed until they split open. It could take three years or more for a small seedling to grow to flowering size. Asclepias purpurascens which is usually found in prairie edges near woodlands, rather than in open prairies, may require high nutrients. Deer tolerant. USDA zone 3 to 8.

WHERE TO FIND THIS PLANT:
Asclepias purpurascens can be found in the 10th Avenue Square, between 16th and 17th Street.

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