Asclepias purpurascens (purple milkweed) looks much like common milkweed. However, common milkweed has grayish-pink flowers, and purple milkweed has reddish-purple ones. It’s difficult to grow in a garden and a rare find in the wild. The genus name of “Asclepias” comes from the Greek god of medicine. “Purpurascens” means “purple”.
I. Appearance and Characteristics
Asclepias purpurascens, the purple milkweed, is a herbaceous plant species. It is in the genus Asclepias, making it a type of milkweed. It is native to the Eastern, Southern and Midwestern United States similar to the range of the common milkweed (Asclepias syriaca). The plant gets its name from the flowers that first develop a pink color but then turn darker purple as they mature. Unlike common milkweed, purple milkweed prefers some shade and is considered a plant of partial shade.
It is also considered an indicator of oak savanna, especially in Wisconsin. The species rarely produces seed pods which are smooth, instead of the rough warty ones produced by common milkweed.
It is listed endangered in Massachusetts and Wisconsin, officially as historical to Rhode Island (though with two recently discovered yet meager pouplations), as imperiled in Maryland and as a special concern species in Connecticut and Tennessee.
All parts are poisonous and toxic if ingested in large quantities.
II. How to Grow and Care
Sunlight
Purple milkweed exhibits its fullest potential under full sun conditions, where it receives unfiltered sunlight for at least 6 hours per day. Its growth and blooming are maximized in such environments, leading to healthier plants and more vibrant flower production. Although purple milkweed can tolerate partial sun, it may result in reduced vigor and fewer blooms, indicating its partial resilience outside optimal lighting. There are no significant changes in leaf coloration or structure as a direct response to light exposure. Outdoor cultivation should be situated in open areas that are well-exposed to natural sunlight to facilitate its best development, as purple milkweed is not commonly grown indoors.
Temperature
It can be planted in most areas if you would remove it after planting for just a year. The suitable temperature range for its growth is 18 to 30 ℃. It can tolerate up to 35 ℃ and withstand a minimum temperature of 8 ℃ in winter. It will stop growing below 5 ℃ and gradually die below 0 ℃.
Purple milkweed likes a humid environment, so provide it with sufficient water in all seasons except winter. If the air humidity is too low, the leaves will gradually lose their luster.
Watering
Originating from North America’s grasslands, purple milkweed is accustomed to periods of moderate drought, exhibiting a preference for drier conditions. This resilience translates into a watering regimen of once every 1-2 weeks, ensuring the soil partially dries between sessions. Indoors, purple milkweed thrives with ample light and well-draining soil, aligning its growth cycle closely with water availability; during active growth, consistent moisture will promote its vibrant flowering.
Soil
Purple milkweed adapts to various soil environments. The most suitable soil is slightly acidic and well-drained. If the planting soil is sticky, add some leaf mold, organic fertilizer, river sand, or a similar compound and stir evenly to improve soil texture. You can also add a little soil at the base of the plant to encourage growth. This will prevent plant lodging and provide more nutrients to the roots.
Fertilizing
Fertilize purple milkweed with balanced nutrition fertilizers to bolster growth and flowering. Use a low-rate, slow-release formula during early spring and again mid-summer. A handful per square meter suffices. Over-fertilization can harm purple milkweed, so precise application is crucial. Seasonal adjustments ensure purple milkweed receives the right nourishment at growth and dormancy phases. Always water purple milkweed after applying fertilizer to disperse nutrients and prevent root burn. For best results, keep a consistent fertilization schedule while monitoring purple milkweed’s response.
Planting Instructions
Purple milkweed can be sown in spring, planted in flower pots or placed directly in the garden. You can keep seeded pots indoors. Sow at warmer temperatures for best results. The seeding depth is about 2.5 cm. Press the soil slightly, so that the soil and the seed make firm contact. After sowing, water the seeds thoroughly. Generally, they will germinate after two weeks with a germination rate of about 80-90%.
When the seeds in the pot germinate with 2-3 pairs of leaves, they can be transplanted into the ground. When transplanting, keep the soil on the roots to avoid damaging the root system. Remember to water thoroughly after planting. Purple milkweed grows best in a ventilated environment, such as by a road, wall, or window. Without good ventilation, pests will appear, which can threaten the plant’s growth.
Pruning
Regularly remove infected plants and wilting leaves to keep purple milkweed healthy. If you are located in a tropical or subtropical climate, you can cut off branches in early spring to promote germination. Given the high toxicity of purple milkweed, wear gloves when handling plants to prevent poisoning. Keep purple milkweed away from children, avoid direct contact, and do not eat the plant.
Propagation
Purple milkweed is effectively propagated by sowing its seeds directly into the soil. To promote successful germination, it is essential to stratify the seeds by refrigerating them for several weeks which simulates the natural wintering process. After stratification, seeds should be sown shallowly, as light aids germination. They require well-draining soil and should be kept consistently moist during the initial growth phase. Care should be taken not to overwater, as purple milkweed does not tolerate excessive moisture around its roots.
Transplanting
The prime time to shift your purple milkweed lies between late winter and early spring, the S2-S3 period, favoring root development before flowering comes. Ensure a sunny to partly shaded location, with well-drained soil. Remember, patience is key – purple milkweed may take time to establish post-transplant.
III. Uses and Benefits
- Ornamental uses
Purple milkweed is perfect for sunny borders, cottage gardens, butterfly gardens, and prairies or naturalized areas.
- Other uses
Like other members of the milkweeds, several insects live off the plant, including the monarch butterfly (Danaus plexippus), the milkweed beetle (Tetraopes tetraophtalmus), large milkweed bug (Oncopeltus fasciatus), small milkweed bug (Lygaeus kalmii) and milkweed leaf beetle (Labidomera clivicollis). Other insects and pollinators feed off the flower’s nectar.
This species is sometimes cultivated in gardens designed to attract butterflies, but is less common than the light purple swamp milkweed (Asclepias incarnata) or the orange butterfly weed (Asclepias tuberosa). The nectar of the plant attracts many other species of butterflies and insects.