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Monarchs and Milkweed By Judy D.

How To Grow Asclepias - Milkweed & Butterfly Weed

By David Salman, High Country Gardens Chief Horticulturist

Asclepias, commonly known as Milkweed or Butterfly Weed, are sun-loving plants that are essential perennials for monarch butterflies providing food for caterpillars and nectar for adult butterflies. Each caterpillar will eat 20 or more milkweed leaves before maturing into a Butterfly. Learn more about Monarchs and Milkweed in our article: Saving The Monarch Butterfly.

The more Milkweed you plant, the better! In addition to attracting butterflies, it will also attract other pollinators, such as beneficial native bees. Milkweed transplants readily as actively growing or dormant plants. You can also start milkweed from seed with a few simple tips. Read on for tips for growing Milkweed.

Watch: How To Grow Milkweed With David Salman


When To Plant Milkweed

Most Asclepias species are late to wake up in the spring, and will often be shipped as dormant plants. These perennial species stay dormant later in the spring than many other plants, especially when they are grown in pots. Don't despair if your milkweed is asleep. The white roots and woody crown are alive just waiting for consistently warm weather to wake up and begin to grow. It's fine to plant dormant plants; don't up-pot them for planting later in the growing season.

Tips for planting dormant perennials: 

  • Don't up-pot them to hold for later planting.
  • Prepare the soil, plant them, mulch, water thoroughly after planting, and wait.
  • Once the weather warms and the plants begin to grow, water thoroughly but infrequently (once every week to 10 days)

Cold hardy Asclepias are great perennials to plant in the fall. Come spring, they are established and ready to host caterpillars on their leaves and feed adult butterflies with their flowers. If you follow the planting tips below, Milkweed can also be successfully planted in spring.

  • Carefully remove the Milkweed plant from its pot by loosening the pot from the rootball. Place your hand around the plant and turning it upside-down to slide the pot off the rootball. Don't tug at the stem, as you could damage it.
  • Before planting, make sure to score the roots with your hands or a pocketknife, so they will spread out into the surrounding soil from the rootball.
  • Water after planting and about three times a week until the plant gets established.

Where To Grow Milkweed: Soil and Light

Asclepias is a widespread genus native to landscapes throughout North America. Generally, these species grow in a wide range of soil types.

Asclepias need at least 6-8 hours of full sun to do their best.

  • Swamp Milkweed (Asclepias incarnata) prefers more moisture and will do better in wet to moderately moist soil conditions. They do well in areas with higher rainfall, such as the eastern U.S.
  • Butterfly Weed (Asclepias tuberosa) does better in dryer areas, such as the western U.S. It needs sandy or gravelly soils. The exception is the Clay form does well in heavier soils, including dry clay. Plant in full hot sun.
  • California Narrow Leaf Milkweed (Asclepias fascicularis) is a western native species of Asclepias, easy to grow in a wide range of soils and recommended for use in the West.

Mulching Milkweed

  • Most Milkweed does not need mulching, except in the hottest climates.
  • In dry areas, Butterfly Weed prefers a gravel mulch.

Watering Milkweed

  • When planting dormant plants, water thoroughly after planting and wait to water again until the plant comes into active growth, at which time a deep watering every week or so is adequate. Take care not to overwater young transplants.
  • After their second growing season, Milkweed only requires deep but infrequent watering. 

Fertilizing Milkweed

  • Use our Root Stimulator Combo Pack (liquid seaweed and SuperThrive) when you water during the first few months in the ground.
  • Avoid fertilizing new transplants, especially with water-soluble chemical fertilizers. Good soil preparation and root stimulator is all they need for their first year.
  • In gardens, fertilize Asclepias just once in fall with Yum Yum Mix.
  • Naturalized plantings don't need additional fertilization. 

General Growing Tips

  • Often Milkweeds won't grow much their first season in the ground, so be patient. They are establishing their root system and crown. By the second growing season, the plants will begin to get bigger and look more robust.
  • The bitter milky sap makes these plants highly resistant to deer and rabbits.
  • Asclepias have a long, carrot-like tap root that should remain undisturbed after planting and should NOT ever be divided.
  • All species of Asclepias are late to emerge in the spring, so don't be concerned if other perennials come up first and they remain dormant.
  • Asclepias syriaca and A. speciosa will spread to make big patches of plants and are best planted in parts of the landscape where they won't crowd out less vigorous plants. Not recommended for the prime spots in your perennial beds.
  • Asclepias incarnata (Swamp Milkweed) is a more refined grower and is fine to include in perennial beds.
  • Oftentimes, Milkweeds won't grow much their first season in the ground, so be patient. They are establishing their root system and crown. By the second growing season, the plants will begin to get bigger and look more robust.
  • To encourage re-seeding and provide winter interest with their ornamental seed pods, leave the stems intact over the winter. In mid-spring, remove old stems just above ground level.

Choosing The Right Milkweed For Your Garden

To learn more about Milkweed varieties, and the relationship between Milkweed and Monarch Butterflies, see our article: Saving The Monarch Butterfly By Planting Milkweed

Milkweed seed pods in early fall

Growing Milkweed From Seed

Neil Diboll, founder of Prairie Nursery in Wisconsin, and a pioneer of prairie restoration says this about seeding Asclepias: "Seeds of all the members of the genus Asclepias that I have worked with benefit from a 30-day Moist Stratification period to break seed dormancy. The seeds germinate best under warm soil conditions. They can be successfully seeded in fall as a “dormant seeding” to improve germination in spring. Fall planting after frost will provide necessary cold stratification.

All species (A. tuberosa, A. syriaca, A. sullivantii, A. incarnata) will also germinate moderately well when seeded into warm ground in mid to late spring with only Dry Stratification treatment."

Seed Stratification

Seeds can be moist-stratified by mixing seed with moist (not soggy) sand in a zip-lock plastic bag and placed in the refrigerator for 30 days. After 30 days of cold moist storage, the seed's natural chemical germination inhibitors have dissipated and are ready to sprout.

Helpful Tips For Growing Orange Butterfly Weed (Asclepias tuberosa)

Orange Butterfly Weed has a deep-growing taproot, and it is much more finicky about the soil in which it prefers to grow. The most commonly available Butterfly Weed seed of this species is grown from populations originating east of the Mississippi and must be grown in sandy, low fertility, acidic soil. It will refuse to grown in heavier, compost-enriched loam, clay-loam, and clay soils. Mismatched soil is the most common reason gardeners have difficulty getting A. tuberosa to grow successfully.

Lauren Springer Ogden, renowned author, gardener, and landscape designer recommends that Orange Butterfly Weed be transplanted before the heat of summer (April-May) or in the fall. She has observed that the combination of wet roots and hot daytime temperatures favor root rot from soil pathogens. She also points out that this species is "highly soil-specific depending on the strain you grow". Lauren also relates that the plants are susceptible to pill bugs. "They will chew where the root meets the crown. And they love warm moist conditions". Another reason to not wait to plant in the heat of summer and not to mulch. This plant is happiest growing in bare, uncovered ground.

Orange Butterfly Weed is also sensitive to growing in damp soil, especially after transplanting. Yellow, chlorotic foliage is usually an indication of over-watering. I recommend that new transplants be watered thoroughly after the initial planting. After the initial watering, wait until the plant begins to wilt slightly before watering thoroughly again. Once you see new growth, a good soaking every 5 to 10 days will be sufficient. Once established, which happens in a few months, the plants may not need much additional water unless conditions are hot and dry. For those of us with drip systems, be sure to place the emitter off to the side of the planting hole so the roots won't sit in overly wet soil.

Plant Milkweed For Monarchs

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