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How to Germinate and Grow Milkweed Seed

Common Milkweed with Monarch Butterfly
Common Milkweed with Monarch Butterfly

Follow our instructions for starting milkweed from seed, including Common Milkweed (Asclepias syriaca), Swamp Milkweed (Asclepias incarnata), and Whorled Milkweed (Asclepias verticillata). We have found these techniques best for good growing results.

Why plant milkweed? Milkweed are the host plant for Monarch Butterflies: the leaves of milkweed plants are the sole food for monarch caterpillars, and the nectar-rich plants are an essenital food source for adult butterflies. The Monarch Butterfly population has declined a whopping 90% over the past decade due to the loss of meadows and habitat (especially in the Midwest). Plant milkweed in your gardens to help support these amazing North American butterflies!

Getting Started: Understanding Milkweed Seed & Germination

Milkweed seeds require cold stratification.

What does that mean? In the wild, milkweed plants scatter their seeds quite late in the season, at a time when the coming cold would kill any seedlings that germinated right away. However, the seeds of milkweeds (and other late-season flower plants) are cleverly programmed to delay germination until after they've been exposed to winter’s cold, followed by gradually rising temperatures in springtime. This adaptation is known as stratification. Cold stratification helps to break the seeds' natural dormancy cycle.  Exposure to winter temperatures help soften or crack the seeds' hard outer casings.

Cold stratification is very important for the germination and growth of Milkweed. 

Without prolonged exposure to cold temperatures, your milkweed seed is unlikely to sprout.

In most areas, when you plant seeds outside in fall, seeds can go through the cold stratification process naturally. If you are planting seed outside, we suggest seeding in late fall so that Milkweed seeds can lay on the ground through winter. This will give your Milkweed seed a long winter of dormancy. Once the sun comes out and the ground is warm in the spring, the seeds will germinate on their own.

In warm zones without winter frost, or if you are starting your seeds in spring, you can cold-stratify seeds in your refridgerator!

Follow our step by step guide: How To Cold-Stratify Seeds For Spring Planting

At-Home Cold Straification Summary: Put your Milkweed seed in a damp paper towel or some damp sand inside a zipper bag, and place in your fridge for 3 – 6 weeks (30 days). Label your seeds, and be sure to choose a low-traffic place inside your fridge where they won’t get damaged.

Milkweed Seedlings
Milkweed Seedlings

How To Germinate Seeds And Start Milkweed Seedlings Indoors

Recommended Supplies:

  • Small 2-4" Peat Pots, or Egg Cartons, or simliar biodegradable planting pots. Water should be able to drain through the peat pots. We've found peat pots to be the best way to transplant milkweed seedlings: See Transplating below.
  • Seed-Starting Potting Soil, rather than general potting soil, will give the best results
  1. Cold Stratification - See above

  2. Start Seeds In Peat Pots - It’s time to plant the cold-stratified Milkweed seeds. Fill the peat pots three-quarters to the top with potting soil. Gently add water until soil is damp. Place 1-2 cold stratified seeds in each pot. Cover with 1/4 inch of soil on top of the seed.

  3. Water - Gently water the planted seed to give additional hydration. The best way to water is from the bottom up:  Use a flat pan under the peat pots and add a half inch of water to the bottom of the tray. Don’t overwater, as it can cause fungus - you want the soil to feel like a wrung-out sponge - damp but not soggy. Water as needed. The best way to test the soil dampness is to touch it; if the soil seems dry then add water, but if it’s wet, wait for the soil to dry out before adding more water.
  4. Wait - Place in a sunny window, in a greenhouse, or under a grow light. Cold-stratified Milkweed seeds should germinate and sprout within 10-15 days after planting. 

Tips For Milkweed Seedlings

Milkweed Seedlings
Milkweed Seedlings
  • Milkweed needs lots of sun and warmth to grow.
  • If you’re using a grow light, make sure to lower the bulb closer to the pots, or your seedlings may become leggy as they stretch to find the light.
  • Ideally, a sturdier stem is better. Some people have good luck pointing a gently circulating fan towards their growing seedlings, in an effort to strengthen young plants.
  • Remember, from stratification time in the fridge to first sprouts can take 40+ days, so be patient!
  • If you plant dry/non-stratified in seed-starting soil and plant in peat pots under a grow light or in a greenhouse to germinate seeds, the success rate will be low and more difficult to accomplish. Without cold stratification, it can take months for the seeds to germinate.

Transplanting Milkweed Seedlings Outdoors

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Transplant shock is the main reason that we suggest planting seeds in peat pots, as Milkweed roots are very sensitive.

You can plant the peat pots directly in the ground, and they will break down over time. The milkweed roots are able to grow through without being disrupted. Be sure there is no top edge above the soil line after transplanting - in dry climates, this will wick away valuable soil moisture.

In most cases, the transplanted Milkweed plant will go though some shock and could lose all of its leaves. This happens, so don’t panic! The plant is putting energy into establishing its roots, and will eventually grow leaves again.

Where To Plant: Milkweed does best in open areas with full sunlight exposure. Remember: fields, parks, cultivated gardens, roadsides, highway medians, and road sides are all favorite places for spotting native Milkweeds.

transplanting milkweed into the ground

When to Plant Milkweed

We suggest transplanting Milkweed when the plant is no larger than 3 inches tall, as many varieties produce a long taproot that cannot be disturbed.

Soil moisture and temperature are very important when growing Milkweed. The best time to put in Milkweed plants is in early spring after the danger of frost has passed, while the best time to plant milkweed from seed is in late fall - this allows mother Nature to take care of the cold stratification for you!

Caring for Milkweed Plants

Once your seedling is planted, water it for a few days to get it established. After that, the plant doesn’t need a lot of supplemental water. Only water if you have an unusual dry spell.

Visit our How to Grow Milkweed page for more details.

Asclepias are somewhat finicky native plants. Minimizing the time they spend growing in a pot and transplanting them as young plants is the best approach.

Are you excited about saving the Monarchs? You can help: learn how to create your own Monarch Waystation, with a collection of milkweed and other nectar plants for Monarch butterflies both young and old.

common milkweed

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