Starting Milkweed From Seed

• By Deborah Harriman
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• August 2023-Vol.9,No.8
• /
• 1 Comment

You may be familiar with the amazing story of a monarch butterfly’s life. The adult butterfly spends the winter high in the oyamel fir forests of Mexico and then starts her annual migration north in the spring. She stops along the way to lay eggs that will develop into the next generation of butterflies. Each generation flies north until finally the fifth and final generation starts its flight south to return to Mexico. There, the monarch butterfly will over-winter with other monarchs until it is time to start the migration again.

The host plant for monarchs is milkweed: monarchs will only lay eggs on milkweed plants, and monarch larvae (the caterpillars) will eat only the leaves of milkweed plants. Unfortunately, development and pesticide use have destroyed habitats and reduced the milkweed supply, nearly decimating the population of this beautiful creature. Piedmont Master Gardeners have explored these topics in two recent articles:

https://piedmontmastergardeners.org/monarch-butterflies-are-at-risk-you-can-help-protect-them/

https://piedmontmastergardeners.org/the-importance-of-milkweed-to-monarchs/

Master Gardeners’ Milkweed Seed-Growing Project

People are increasingly concerned about the plight of monarchs, so organizations and individuals have planted milkweed patches to create Monarch Waystations that will sustain monarchs on their long journey. However, milkweed plants can be hard to find, and local nurseries have limited supplies. This led a small group of Piedmont Master Gardeners to aid this effort. Our group grew milkweed from seed to offer to the public at our Spring Plant Sale. This article describes several seed-starting methods and shares tips for those who want to try growing their own milkweed plants.

IDENTIFY PLANTS

According to the Biota of North America Program ( BONAP ) milkweed plants most prevalent in the wild in the Central Virginia Piedmont region are common milkweed (Asclepias syriaca), butterfly weed (A. tuberosa), swamp milkweed (A. incarnata), and whorled milkweed (A. verticillata).  Taking the importance of locality one step further, growing plants of local ecotypes is considered a best practice. These are plants native to a region, that have adapted to that region over time. Their genetic make-up is more like other species in the same region than to the same plant from another region.  marylandgrows.umd.edu/What are local ecotype plants and why do they matter to pollinators?

Trying to harvest milkweed seeds of the same local ecotype would mean collecting in the wild. That would be a difficult proposition if we wanted to control the process and provide lots of plants for sale. Some Master Gardeners did gather common milkweed seeds from the wild, but most seeds were collected in our own gardens. Common milkweed, butterfly weed, and swamp milkweed were the most available to us, so our project focused on those varieties.

DETER PESTS

Milkweed plants must escape being eaten by predators, if flowers and then seeds are to form. The sap contains toxins called cardiac glysosides or cardenolides, which make it poisonous to animals if eaten in large quantities. Despite its reputed unpalatability, deer and rabbits will munch on milkweed.  In fact, deer ate every bloom on my butterfly weed this past spring. To deter mammal browsing, install physical barriers, such as fencing, or string several pieces of monofilament between stakes around the bed. For a less unsightly tactic, spray aromatic barriers or sprinkle deer deterrent pellets around the area. While both are effective, the key to using them is to apply them frequently and switch products regularly, because deer become accustomed to those odors and will eventually ignore them.

Net bag protecting a developing seed pod. Photo credit: Anne Nelson

The milkweed bug (Oncopetus fasciatus) is a common pest on milkweed. The small bright orange nymphs cluster on the flowers when they bloom. The adults are large, bright orange bugs with black markings. Milkweed bugs are active for only a short time and not a danger to the plant. They feed on the seeds by piercing the milkweed pod with their long proboscis. Thus, these bugs are a problem if seeds are going to be collected.

Handpicking milkweed bugs off and dropping them into a jar of soapy water or applying insecticidal soap are effective controls. But killing them all removes them from the ecosystem, which is usually not desirable. For example, when milkweed bugs eat the seeds, that prevents milkweed from spreading and becoming too abundant. A better method is to preserve some of the seed pods for collection, while letting nature take its course with the others. Small pieces of netting or net bags can be tied around a few pods before the insects become active. The net bags commonly used as party or wedding favors are available in craft stores and online. Bags can be left on the pod, and seeds will continue to form until it’s time to collect them.

COLLECT AND STORE SEEDS

Milkweed seeds form inside pods attached to a mass of delicate floss known as coma. Once the pods open, the floss wafts in the air until the seeds land and eventually germinate. There is so much floss in each pod that it was historically used to stuff pillows and mattresses. Naturally buoyant and water-repellent, this floss was used to fill life jackets for soldiers in WWII.

The abundance of floss can make seed collection a challenge, but certain techniques can make this process easier. Late summer or early fall is the time to start collecting. Not all pods ripen at the same time, so look for pods that are mature and have started to turn brown. Look for those that are not yet split open. They may still be somewhat green.

When pods are ready, apply slight pressure at the seam to pop the pod. You will see seeds packed tightly in rows along the floss. If seeds are dark brown, they are ripe and ready to collect. If they are white or tan, they need to mature on the plant a little longer. When timing is right (before the floss expands), squeeze the pod until it pops, grab its narrow end, and pull out the whole rib. Rake your finger along the seeds, going with the grain of the seed to separate them from the floss, and put them put into a container. This video from Project Monarch Watch is a good tutorial:  https://www.youtube.com/watch?v=aFXWitrxOmQ.

After the pods pop open naturally, wind will carry the floss with seeds attached, dispersing them to the ground. It’s best to collect only some of the milkweed seeds from a plant, so the rest can spread on their own. To avoid mold, be sure the seeds are completely dry before storing them in envelopes, paper bags, plastic bags, or air-tight containers. Keep seeds in the refrigerator or another cool, dry area until planting time.

 PLANT SEEDS

The PMG group used several methods (described below) to germinate seeds.

Outdoors in the Fall

In nature, seeds fall to the ground where soil, leaves, or snow slowly cover them. The long winter in a cold, moist environment softens their hard husk and breaks their dormancy, so they can germinate with rising spring temperatures. This process is called stratification. The laissez-faire gardener can mimic nature by scattering the collected seeds on a raked, weed-free area in the fall to let nature take its course. This previous article discusses a Master Gardener’s experiences planting common milkweed outdoors in the fall.  https://piedmontmastergardeners.org/article/milkweed-in-the-garden/

Milkweed is difficult to transplant once it is growing. Therefore, our group decided to try other methods to improve germination rates and provide plenty of milkweed plants for the public at the spring sale. 

Indoors under Lights

For speedy germination and more control over the process, some Master Gardeners started milkweed seeds inside under lights. With this method, it’s necessary to artificially create the cold stratification process. In early January, wrap the seeds in a single layer in damp (but not wet) paper towels, coffee filters, or in dampened vermiculite and place them in resealable plastic bags. A dry paper towel can be placed on the damp towel to absorb excess moisture. Store in the refrigerator (not freezer) for 30 days. Monitor seeds weekly to be sure the medium and seeds do not dry out.

After 30 days of stratification, plant the seeds in dampened seed starter mix in cell packs, small pots, peat pots, or seedling trays. Top with a dusting of vermiculite or chicken grit. Cover the trays with plastic domes and set under the grow lights. The pots or trays can also be placed on heat mats to speed germination. If used, remove those mats after seeds sprout.  Water the pots from the bottom rather than from the top so the water seeps up to the roots. Keep the foliage moist by occasionally giving seedlings a spritz with a sprayer. Place the grow lights close to the seedlings, so they do not stretch toward the light and become weak. After seeds sprout, remove the plastic cover to allow good air flow. You can also use an oscillating fan to mimic outdoor breezes and promote stronger stems. Transplant the seedlings to larger pots as they grow. When the weather warms in March, “harden” off the seedlings by moving the pots outdoors during the day and back inside at night. After a few days, the pots can be kept outdoors, but move them into a porch or garage if freezing temperatures are forecast.

In a Sunny Window

No lights? No worries. Common milkweed is a reliable germinator. After the stratification process, one Master Gardener sowed the seeds in cell packs, sprinkled them with chicken grit, and placed them in a sunny, south-facing, window. She covered the seeds with a plastic dome and placed the pots on a heat mat. She watered from the bottom to keep soil moist and removed the mats and domes when seedlings appeared. When the weather warmed up, she moved the seedlings outside, following the hardening off process described above.

In Plastic Containers or Gallon Jugs

For a semi-controlled but less finicky process than using lights, some Master Gardeners sowed seeds in plastic containers and milk jugs. Seeds sown in the ground outdoors are at the mercy of Mother Nature. They can wash away, rot in wet soil, dry out, or be consumed by animals. Starting seeds outdoors in containers enables the moist, cold stratification process naturally, while protecting seeds from the vagaries of nature. Here is the step-by-step process.

Clear plastic produce boxes make ideal seed-starting containers. Good drainage is necessary, so if there are no holes, punch plenty in the tops and bottoms. Fill with about 4 inches of moist seed-starting mix or other potting mix. After sowing the seeds, cover with a dusting of vermiculite or coarse sand (do not use playground sand because it is too fine), and close the lids. Place the containers outside in a sunny location away from wind. To ensure good drainage, place them on a table off the ground. They should be fine all winter, but check them periodically to see if they need water. If the area becomes shady when trees leaf out, move the containers to a sunny spot. After seeds germinate (mid to late March), remove the lids, put the containers in the sun, and water as needed. When there are several sets of true leaves, transplant the seedlings to larger pots.

Photo credit: Deborah Harriman

Winter sowing in gallon jugs requires some preparation, but then you can “set it and forget it.”  Collect and wash a few one-gallon plastic milk or similar plastic jugs. Toss out the caps, since you will leave the jugs open to winter precipitation. Use a marker to delineate a cutting line around the jug, just below the handle. You can rest a marker on a coffee cup and turn the jug around to ensure the line is level all around it. Use a box cutter or sharp scissors to cut along this line, but don’t cut the section under the handle because this will serve as a hinge. You now have a “pot” with a closable dome attached.

Poke or drill plenty of holes in the bottom of the jug. If available, a drill is the easiest method. Place the bottom of the jug on a wooden board to give the drill some purchase as it spins. In mid-December or early January, fill the jug with damp (but not soggy) potting soil; this should be several inches from the top of the jug. Sprinkle the milkweed seeds over the soil and spread a thin layer of coarse sand, vermiculite, or chicken grit over the seeds. No further watering is needed. Close the dome and seal the cut with 2-3 layers of duct tape. The top, where the cap used to be, should remain open. Place sealed jugs in a sheltered spot to begin their long winter’s nap.

Photo Credit: Melissa King

If wind or marauding animals are a problem, place the jugs in milk crates, so they won’t topple. If the jugs are under trees or in the shade, move them to a sunnier spot after trees start to leaf out in spring.

These seeds will gradually undergo stratification and should sprout by mid to late March. This waiting period may test your patience, but have faith in the process. Observe regularly. When seeds begin to sprout, cut open the jugs and move them to a sunny spot. Water the open jugs as needed. When the seedlings have several sets of true leaves, transplant them into small cell packs or individual pots.

No matter which method you choose, seedlings can be transplanted into the garden when they have four sets of true leaves and are about 3 inches tall. Disturb the roots as little as possible during this process, especially common milkweed and butterfly weed, which develop long tap roots. You can plant seeds started in peat pots directly into the garden, but make sure the rim of the pot is not above the soil.

Photo Credit: Melissa King

Milkweed should be planted in areas that meet its cultural needs: dry for common milkweed and butterfly weed, but moist for swamp milkweed. Remember that all varieties of milkweed need plenty of sun. It takes time for roots to develop, so don’t be disappointed if milkweed plants don’t bloom during their first year.

SUMMARY

Our group of Master Gardeners discovered that starting milkweed seeds under lights indoors or winter sowing in containers outdoors are both effective methods. We successfully cultivated 400 milkweed plants to sell to the public. Using lights resulted in quicker germination and larger plants by early May, but winter sowing was easy and fun. Collecting, stratifying, and seeding was an excellent learning process, and we hope other gardeners will try it. Our collective efforts will help monarchs survive in the years to come.

Tips for starting milkweed seeds:

• Dry seeds before storing them.
• If starting inside, stratify seeds for at least 30 days (the paper towel should be damp, not wet).
• Use seed starting mix or other reliable soil-less potting mix.
• Starting mix should be damp, but not wet.
• Label pots with date and milkweed species; a permanent marker works well.
• Remove domes or open lids on containers when seeds geminate.
• Once seeds in pots germinate, water from the bottom (not from above).
• Thin seedlings in plastic containers or jugs to ensure good airflow and promote stronger root development.
• Seedlings started inside should be hardened off before being moved outside.

Featured Photo:  Deborah Harriman

Resources

5 Steps to Planting Milkweed Seeds Indoors, (Save Our Monarchs)

Harvesting Milkweed Seed: A Pod and A Plan, (Xerces Society)

How to Collect and Grow Milkweeds to Help Monarchs and Other Pollinators, (Michigan State University Extension)

Milkweed Bugs, (Missouri Botanical Garden)

Milkweed FAQS,  (Xerces Society)

Monarch Butterfly Habitat Needs (U.S. Forest Service)

Native Milkweed Germination Guide (Oklahoma State University)

Starting Seeds in Winter ( Penn State Extension)

The Biota of North America Program (BONAP)

Why Milkweed  (Monarch Joint Venture)