Antelope/Spider Milkweed Seeds - (Asclepias asperula)

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Seed Count:
Approx 20 seeds per pack
Seed Sales Support:
Arizona Milkweeds for Monarchs
Elevation Range:
2,500 - 9,000'
up to 3' tall
Native, Non-Hybrid, Non-GMO seeds
  • Antelope or Spider Milkweed flowers - (Asclepias asperula)
  • Carpenter Bee on Antelope or Spider Milkweed flowers - (Asclepias asperula)
  • Monarch butterfly larvae on Antelope or Spider Milkweed leaves - (Asclepias asperula)
  • Antelope or Spider Milkweed seed pod - (Asclepias asperula)
  • Antelope or Spider Milkweed Seeds - (Asclepias asperula)

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Frequently bought together:


Antelope/Spider Milkweed -  (Asclepias asperula)

Antelope Horns Milkweed - also called Spider Milkweed, Green-flowered Milkweed, and Spider Antelope-horns - are named for the way mature seed pods curve upward approximating the form of an antelope horn. The stem is green lightly tinged with maroon, bearing leaves that are long, gently arcing and V shaped, rising upward from each central vein. Abundant round erect clusters bear stiff pale greenish white and maroon flowers. Plants normally grow up to 3' tall and are native to Arizona and regions of the Southwest. 

This milkweed is resilient and very hardy, preferring full sun and thriving in adverse conditions. It only needs about 8" of annual moisture and is relatively indifferent to soil, happily growing in rocky soils and tolerating minimum winter temperatures down to -10 to -20°F. It flourishes in more fertile climates like the US Midwest with up to 50" of moisture and richer soils.


Throughout the warm season from April through September.

Will These Grow in My Area?

The range of these milkweed species is not limited to Arizona but in most cases the entire southwest and beyond. Refer to the USDA map link and please realize that a milkweed species can grow and thrive outside of the areas listed if the conditions are favorable.

From that link, you’ll see the states shown where the milkweed is native. If you find a state that has areas with climate and conditions similar to yours, then that milkweed will most likely do very well for you. 


Milkweed pods contain a seed floss that is used to stuff pillows or mixed with other fibers to make a cloth. It is used in Life Jackets or as a stuffing material. It is very water repellent. The floss is the mechanism for seed dispersal.

Other Names

  • Silkweed
  • Spider Antelope Horns
  • Antelope Horns

Planting and Growing Tips

Milkweed has an intriguing way of guaranteeing its survival. In the autumn, when the seed pod ripens and bursts open, the seeds are dispersed by the wind. Each seed has a natural coating that prevents it from germinating. This protective layer ensures the seeds will not sprout prematurely during the colder months when they might not survive the frost and harsh weather conditions. 

During winter, moisture and soil gradually wear away the protective layer of seeds. When spring comes, and the temperature increases, the seeds can absorb moisture and start the germination process. This natural timing ensures that the seedlings emerge when the environmental conditions are most suitable for growth and survival.

You can plant Antelope Milkweed seeds in spring and fall, whichever suits your needs better. 

Two methods for planting these seeds are cold stratification and direct sowing. The approach you choose should depend on when you want to plant and your garden's climate. First, we'll guide you through the cold stratification process. Then, we'll discuss the advantages and disadvantages of both methods.

Cold stratification imitates winter conditions to jumpstart germination, and it can be done easily at home!

First, label a sandwich-sized ziplock bag with the name of the milkweed and the date. Fill the bag about 3/4 full with sand, decomposed granite, or another abrasive material. Then, add enough water to moisten the sand thoroughly – you should see a sheen of water when you gently squish the bag.

To start, put your seeds into the mixture. Make sure to stratify only as many seeds as you plan to plant, and add only one variety of seeds to each bag. After that, seal the bag and put it on the top shelf of your refrigerator. You should move it a couple of times daily to imitate the natural winter conditions that trigger the germination process, which is aided by the cool, wet, and abrasive environment.

After approximately one month of cold stratification, your seeds will be ready to plant. Follow the usual planting instructions and watch your seeds sprout into healthy, vibrant plants.

Pros and Cons of Each Approach

Both cold stratification and direct sowing are viable methods for planting Antelope Milkweed seeds, each with its own advantages and drawbacks.

Cold Stratification 


  • Improved Germination – Cold stratification significantly increases germination rates by mimicking the natural winter conditions that trigger the seed to sprout. This process breaks down the seed's natural dormancy, leading to a higher percentage of successful germination and a more uniform emergence of seedlings.
  • Earlier Emergence – Seeds that have been cold-stratified tend to germinate sooner in the spring than those sown directly outdoors. This head start gives seedlings more time to establish themselves and grow before the heat of summer arrives.
  • Controlled Environment – Cold stratification occurs indoors, typically in a refrigerator, providing a protected environment for the seeds. This shields them from pests, diseases, and unpredictable weather conditions that could otherwise hinder germination.


  • Requires Preparation – Cold stratification requires some planning and preparation before planting. This involves gathering materials like sand or vermiculite, moistening them, and placing the seeds in a sealed container or bag for the designated period (usually around 4-6 weeks for Rush Milkweed). Additionally, you'll need to monitor moisture levels and ensure the seeds don't dry out.

Direct Sowing


  • Simplicity – Direct sowing is a straightforward method involving planting seeds directly into the ground without pre-treatment. It eliminates the need for extra steps like cold stratification, making it a convenient option for those who prefer a simpler approach.
  • Natural Process – By planting seeds directly outdoors, you allow them to germinate naturally in their intended environment. This can result in stronger, more resilient seedlings that are adapted to your garden's specific conditions.
  • Large Scale – Direct sowing is ideal for planting large quantities of seeds, such as when establishing a wildflower meadow or creating a large milkweed patch for Monarch butterflies.


  • Lower Germination – Germination rates for direct-sown seeds are typically lower than those that have been cold stratified. This is because the seeds may not experience the optimal conditions for breaking dormancy and initiating sprouting.
  • Vulnerability to Pests – Seeds sown directly into the soil are exposed to various pests, including birds, rodents, and insects. These creatures may eat the seeds or damage young seedlings before they have a chance to establish themselves.
  • Unpredictable Weather – Unfavorable weather conditions, such as extreme temperatures, heavy rains, or drought, can negatively impact germination and seedling survival.

Why This Milkweed is Special

This milkweed seed is of the highest quality available anywhere. It has been meticulously hand-grown across central and northern Arizona and then carefully hand-harvested, hand-cleaned, and hand-packed to ensure its purity. Since 2018, it has been test-grown at different elevations to verify its vigor and adaptability to different conditions. 

Terroir Seeds is honored to be the exclusive partner in offering these exceptional milkweed seeds to home gardeners. The sale of each seed packet supports the research of the Arizona Milkweeds for Monarchs organization, which is a dedicated group of volunteer citizen scientists overseen by professional scientists from Northern Arizona University. 

The milkweed plant, scientifically known as Asclepias spp., is essential to the Monarch butterfly's life cycle. Monarchs travel across the United States every spring, laying eggs on native milkweed plants. These plants are the only source of food for newly hatched monarch caterpillars. Arizona boasts over 40 species of milkweed, which accounts for more than 50% of the total diversity of milkweeds in the continental US. This diversity of milkweeds makes Arizona second only to Texas in terms of its variety of milkweeds. 

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2 Reviews

  • 5

    Excellent germ rate and fast, too

    Posted by Jason on Jan 10, 2024

    I did the water method to germinate these, no cold stratifying, and on the third day had 90% germination. Really great results from excellent seeds.

  • 5

    Good seeds!

    Posted by Kathy on Jan 02, 2019

    Looking forward to many Monarchs!

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