Grow milkweed in pots

How to collect and grow milkweeds to help monarchs and other pollinators

Fluffs of white appear along country roads in Michigan every fall – the seed pods of milkweed plants. These little, fluffy seeds hold a lot of potential for monarchs passing through Michigan, and are important to many bees. The beautiful flowers of milkweeds produce pollen and nectar for bees, butterflies and other pollinators. More milkweed in Michigan means more food for pollinators, and more places for monarchs on their migration. Butterflies and bees can use your help in planting more of these plants. Michigan State University Extension offers the followings steps on what you can do.

Grab a friend, bring a kid, put the dog on a leash and go out and collect milkweed seeds! Bring envelopes or baggies and a marker so that each species can be kept separate. Milkweeds grow well in disturbed areas, so scout in ditches, pastures, field edges, medians, etc. (Make sure you get permission before you go on any private land.)

  • Look for different types of milkweeds. There are about a dozen types of milkweed that are native to Michigan – you can check out their ranges at the Biota of North America’s Plant Atlas. You can also see what types of milkweed seeds are needed in your region through this map on Monarch Watch.
  • Seed pods should be open, dry and brown. If you aren’t sure, give the pod a squeeze – it should pop open easily. If pods are still green or white, keep a note where they are and come back later.
  • Grab some seeds from many different plants. Many milkweeds are clonal, meaning plants in a group are closely related. To get lots of diversity, collect seeds from plants in many areas. You can collect a lot from common ones like common milkweed (Asclepis syrica), butterfly weed (Asclepis tuberosa) and swamp milkweed (Asclepis incarnate), but only a little from ones that are rarer.

Common milkweed (Asclepis syrica). Photo by Duke Elser, MSU Extension.

Butterfly weed, also known as butterfly milkweed (Asclepis tuberosa). Photo by Duke Elsner, MSU Extension.

Swamp milkweed (Asclepis incarnate). Photo by David Cappaert, MSU, Bugwood.org.

Older milkweed plants are very difficult to transplant, so we do not recommend transplanting older, large milkweeds.

What do you do with milkweed seeds?

You can plant them immediately this fall. October and November work well in Michigan – you want the soil to be too cold for the seeds to germinate, but not yet frozen. Choose a sunny corner where the milkweeds can spread. Create a patch of bare soil and water it so the soil is moist. Use your finger to poke holes in the soil and drop a seed in each hole. Cover and wait for spring! For more tips on fall planting, see “Fall Planting Milkweed Seeds – 10 Simple Steps!” from Monarch Butterfly Garden.

Miss the window for fall planting? You can winter sow many types of milkweed. Use old, plastic containers like yogurt containers. Poke a few holes in the bottom for drainage and fill with a few inches of potting mix. Dampen the mix and plant the seeds, covering them lightly with more soil. Poke a few holes in the lid and cover your container. Put your container outside in a shady spot, like the north side of your garage. For more tips on winter sown milkweed, see “Winter Sowing Milkweed Seeds Part 2: Prepare Your Containers” from Monarch Butterfly Garden.

You can also plant milkweed in the spring! You have to take care of the seeds to make sure they will be viable for spring planting.

  • Remove the fluffy white coma, or the little seed parachutes. You want to only store the little brown seeds. You can remove these by hand or by putting them all in a paper bag and shaking vigorously.
  • Make sure your seeds are free from pests. Milkweed bugs can pierce holes in the seeds, ruining them. Make sure there aren’t any insects or extra plant material in with your seeds. See photos of milkweed bugs and get more tips on saving seeds.
  • Give your seeds a winter. Milkweed seeds, like many native plants, need to feel a cold winter before they can germinate. This process is called vernalization and can be done many ways. The simplest is to put seeds in moist soil or peat and store in an old refrigerator. If you don’t want soil in your refrigerator, you can also layer seeds between moist paper towels in a baggie in your crisper, keeping them cold for a minimum of three weeks and up to three months.
  • Start seeds indoors four to six weeks before transplanting outdoors. Milkweed seeds can be direct sown in spring, but transplants have better success. Fill pots or trays with light, well-drained soil. Add the seeds and cover with 0.25 inches of soil. Keep soil moist and pots in a sunny, warm spot or under grow lights.
  • Transplant outdoors. Once the danger of frost has passed and the milkweed starts have four true leaves, they are ready to go outside. Clear a patch in a sunny spot, giving each plant plenty of room to spread its roots. Water frequently until your plants are established.

Not able to collect enough seeds?

You can purchase milkweed seeds and plants at the following places:

Here is a table of commercially available milkweeds for Michigan.

Commercially available milkweeds for Michigan

Common name

Scientific name

Native range in Michigan

Available as

Common milkweed

Asclepias syriaca

Throughout

Seed

Butterfly milkweed

A. tuberosa

Throughout

Container plants and seed

Swamp milkweed

A. incarnata

Throughout

Container plants and seed

Whorled milkweed

A. verticillata

Southern Lower

Seed

Tall milkweed

A. exaltata

Throughout

Container plants

Prairie milkweed

A. sullivantii

Southern Lower

Container plants

Not able to plant milkweed?

Even if you don’t have enough room to plant milkweed, you can help by volunteering for seed collection trips with a local Land Conservancy, or by donating your seeds to other projects that help monarchs. To donate, visit Monarch Watch and view a list of some Michigan Land Conservancy programs.

Register your site as a Monarch Waystation

Show your dedication to monarch conservation by registering your site as a Monarch Waystation. It will show up on the International Monarch Waystation Registry, and you can order a sign to teach your neighbors about monarch conservation. Additional information to certify your waystation, including kits, brochures and information, can be found at Monarch Watch, as well as the applications for Monarch Waystations and a guide to creating a waystation.

More resources on planting milkweed

  • Growing Milkweeds by Monarch Watch
  • Create Habitat for Monarchs by Monarch Joint Venture
  • Finding, Collecting, and Growing Milkweed by University of Minnesota Monarch Lab
  • Monarch Watch Milkweed Market
  • Milkweed Facts by Xerces Society
  • Milkweeds: A Conservation Practitioner’s Guide by Xerces Society

Plant milkweed to help save the monarch butterflies

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In 2014, I came across one of the most clever uses of a hashtag I’ve seen on social media: #GotMilkweed. The hashtag was part of a campaign launched by the David Suzuki Foundation that aimed to create a monarch butterfly corridor in Toronto. (For readers who live in the U.S. and abroad, David Suzuki is a prominent scientist and environmentalist here in Canada.)
The statistics are grim. Scientists have been reporting staggeringly low numbers of monarch butterflies that migrated to Mexico, partly due to the eradication of milkweed across North America. The milkweed plant is not only an important food source for monarch caterpillars, it’s the only plant on which a monarch butterfly will lay its eggs. (2016 update: A World Wildlife Fund survey suggests “migratory monarchs are rebounding—but with a long road ahead.”)

In the last couple of years, scientists have been encouraging gardeners to plant milkweed to help the monarch butterfly population. I planted some in my garden and asked wildflower guru Miriam Goldberger, author of Taming Wildflowers (St. Lynn’s Press, 2014) for some advice.

A few tips for purchasing and planting milkweed

“It’s unfortunate that such a beautiful and important plant in our North American ecosystem is named a weed,” says Miriam. Common milkweed (Asclepias syriaca) is the source of the plant’s bad reputation—it’s quite invasive. Here in Canada, it also used to be on the Ministry of Natural Resources’ noxious weeds list.

Common milkweed (image courtesy of Miriam Goldberger)

The good news is there are other types of milkweed that don’t spread. “Monarchs will also enjoy red milkweed (Asclepias incarnata) and butterflyweed (Asclepias tuberosa),” says Miriam. “Both of these are host plants for the adult monarchs as they lay eggs, and as food source hosts for the larvae (caterpillars). These two alternatives do not spread by rhizomes and are employed by monarchs just as often as the common milkweed.”

Miriam says that red milkweed will grow in any soil type, but it prefers medium to moist soils. It likes full sun (though it will tolerate a bit of shade). “Butterflyweed will also tolerate some shade, but is a bit more picky about its soil type, preferring sand or loam. Dry to medium soils are preferred,” she says.

Butterflyweed (image courtesy of Miriam Goldberger)

And, you can still plant common milkweed, says Miriam, especially if you have dry, clay soil. You should plant it with a combination of other native flowers and grasses that take up the various levels of soil, she warns. “Common milkweed spreads by rhizomes (underground runners or roots) which is why it can be such an aggressive spreader. By planting it within a fairly dense planting of other native species, you leave minimal room for the rhizomes to travel.”

Miriam says liatris, goldenrod and asters are other forms of monarch nutrition that you can add to your garden.

Sadly, in the last few years I haven’t seen many monarch butterflies flitting throughout in my garden. I’ve spotted a few other types, especially around my buddleia, but I want to make sure the monarchs find a welcoming spot in my garden, too. I eagerly spread the #GotMilkweed message so other gardeners could add it to their must-plant lists. “Anything that brings forward the issue of native pollinator health is a good thing,” agreed Miriam, who says the monarch butterfly issue is coming to light, largely due to David Suzuki and his team’s efforts. “He is raising awareness in a way that only David Suzuki can and it’s proving to be a positive step forward.”

Where to buy milkweed

A local native plant sale is a good place to begin your hunt for milkweed. Ask your local nursery manager if the store will be carrying any native varieties this spring. Miriam sells seeds through her Wildflower Farm website. In Nova Scotia, Baldwin Nurseries sells plants. Botanical Interests offers Asclepias speciosa.

Main image (red milkweed) courtesy of Miriam Goldberger

Creating A Container Garden Waystation

A Monarch Waystation simply is a garden that has both milkweed and nectar plants and just as you can grow these plants in the ground, you can also do it in containers that you keep on your deck, balcony, front steps or elsewhere around your home. All you need is pots, soil, plants and water.

Which pot? Larger pots (at least 18” wide) made of plastic are preferred. Perennial plants (milkweeds and nectar plants) have longer root systems and need room to grow year after year, so choose a pot that is at least 18″ deep as well. Larger pots also provide more protection from cold, enabling perennials to overwinter more successfully.

Choose pots that have good drainage. Include pieces of a broken clay pots or gravel in the bottom of your pot to promote drainage. Plastic pots are preferred over clay because they do not allow as much moisture to escape. Clay can also break in the winter.

Soil & Water: Use standard gardening soil with a small amount of compost. Soak soil well prior to planting, then plant plants and water well so that soil is saturated. Water plants as needed through the summer so they do not dry out.

Recommended plants for Container Garden Waystations:
– Milkweeds (native, perennial): Butterflyweed and Swamp milkweed
– Nectar plants (native, perennial): asters, goldenrods, rudbeckia/coneflowers, liatrus, coreopsis
– Nectar plants (non-native, annual): Lantana, verbena, zinnia, cosmos, Mexican sunflower

Care: Through the summer, you can deadhead the flowers to encourage further blooming. Collect seeds from annuals to use next year and collect seeds from perennials to share with friends or scatter outside.

Overwintering perennials in pots:
– In late fall, cut old stems down to 4″ height.
– Wait until plants are dormant (temperatures into the 30s) to overwinter them
– Group pots close together to provide greater warmth/protection.
– Water thoroughly before temperatures dip and the ground freezes. This provides some water through winter and some protection from the cold.
– Overwinter your plants either inside an unheated garage, a shed or outside in a sheltered spot on the ground (the ground will provide some warmth. A raised deck or pavement is too cold)
– Overwintering outside (on the ground or in a shed): Cover the pots/plants with leaves for insulation.
-Overwintering inside a garage: Provide water occasionally just to slightly moisten the soil. Look for a spot that stays 32-45°F.
– Late April, early May take your plants back out to their regular locations, water and watch them return.

More tips can be found online for overwintering plants. It requires some care but is quite satisfying to do.

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Introduction
Milkweeds can be propagated from seeds, cuttings, and, in some cases, from root divisions. This account will deal with storage, treatment and planting of milkweeds seeds and will briefly touch on propagation from cuttings.

Milkweed seeds can be planted in prepared beds outdoors or started indoors in flats. We recommend the latter approach since germination rates are generally higher indoors and it is easier to establish your milkweeds with transplanted seedlings that are well-rooted and therefore more resistant to weather extremes and pests.
Germinating, Growing and Transplanting
Milkweed seedlings can be started indoors in a greenhouse or under artificial lighting and then transplanted outdoors after the average date of last frost. If seeds are started indoors, allow 4-8 weeks growing time before transplanting. Plastic flats can be used to start the seeds. Fill the flats with a soil mix suitable for seedlings (most potting mixes are), thoroughly soak the soil, and let the excess water drain. Sow the seeds by scattering them on the soil surface 1/4-1/2 inch apart, and then cover with about 1/4 inch of additional soil mix. Gently mist the soil surface with water to dampen the additional soil mix that has been added. In an effort to improve germination rates, many gardeners place the seeds in packets made from paper towels and soak them in warm water for 24 hours prior to planting. This method seems to work especially well for seeds of species that require stratification.
After the seeds are sown in the flats, cover each flat with a clear plastic cover or a plastic bag to keep the seeds from drying out while germinating. Then, place the flat under grow lights, in a warm sunny window, or in a greenhouse. Most seeds will germinate in 7-10 days if the flats are maintained at 75˚F. After the seeds have germinated, remove the plastic covering from the flats. Once the seedlings have emerged, the soil should be kept moist by watering the flat from the bottom. You can water from the bottom by placing the flat in a sink or a larger flat filled with 2 inches of water until moisture appears on the soil surface. The soil should be kept moist but some care is needed to keep the seedlings from getting too wet – such conditions contribute to fungal growth that can kill the young seedlings (“damping off”). Thinning (see below) can reduce damping off.
The plants are ready to be transplanted when they are about 3-6 inches in height. Before transplanting, acclimate the plants to outdoor conditions for a few days by placing them in a sheltered location during the day and then bringing them indoors at night. The seedlings should be planted 6-24 inches apart depending on the species (check the back of your seed packets for information). Newly transplanted plants should be watered frequently. Add mulch around the seedlings soon after planting. The mulch holds in the moisture and minimizes the growth of competing weeds. The seedlings should be fertilized 2-3 times during the growing season if using water-soluble fertilizer or once a season if you utilize a granulated time-release formulation.
Thinning
When small seeds are sown, they are often mixed with sand or fine soil to have better seed distribution. However, this method does not completely prevent crowding of seedlings and thinning will be necessary. Thinning provides more space between plants, increasing the amount of light reaching the plants and the air circulation around them. Seedlings may need to be thinned several times beginning 1-2 weeks after germination. Without proper thinning, you will end up with weaker plants.
When to Plant
Milkweed seeds can be sown outdoors after the danger of frost has passed. Refer to the seed packets for special instructions on sowing the seeds. Keep in mind that seeds have a range of soil temperatures at which they will germinate. Also, remember that under sunny conditions the soil temperatures can be much higher in the daytime than the ambient air temperatures you experience. Plant the seeds early since those planted late in the season may not germinate because of high temperatures. In addition, new seedlings from late plantings can “dry off” before they are even noticed. Asclepias incarnata (swamp milkweed) and A. syriaca (common milkweed) germinate poorly at high temperatures (>85˚F). However, other species such as A. curassavica (tropical milkweed) and Cynanchum laeve (blue vine) germinate well at these temperatures. Germination outdoors depends on soil moisture and temperature and could take several weeks if conditions are not ideal.
Preparation of the Seedbed
If you are gardening for the first time, it is wise to consult with your local county extension agent to see if your soil needs to be enhanced (amended) with soil additives before planting the seeds.
A smooth, clump-free, weeded soil bed will virtually guarantee a successful start for germination and seedling establishment. If vegetation exists in the future habitat location, it can be removed by using a tiller or by hoeing the area. To reduce clumping, do not work the soil when it is wet. The soil should be worked to a fine consistency to ensure good soil to seed contact.
The seedbed should be kept moist until germination. As the seedlings become established, it is important to avoid watering too much or too little. A light watering each day until roots are well established (7-10 days), preferably in the morning, should be sufficient.
Growing Milkweeds from Cuttings
All milkweeds are perennials and some can be grown from cuttings. Cuttings provide a way producing new plants in a relatively short time and it avoids some of the difficulties of starting plants from seeds. To start cuttings, cut the stems underwater, then coat the bottom of the stem with a strong rooting hormone. The stems should be placed in sand, vermiculite, or potting soil that is kept continuously moist. Cuttings can usually be transplanted in 6-10 weeks. Survival is best when cuttings are made from green stems (1/3 inch diameter) obtained from plants fertilized two weeks earlier.
Soil Types
If you have a choice, light soils are better than those with heavy clay. Well-drained soils are generally best but there are some species, e.g. A. incarnata (swamp milkweed) and A. sullivantii, which do well in saturated conditions.
Where to Plant
Most milkweed species evolved in open areas where they were exposed to full sunlight and they will do best if they are planted in the sunniest areas of your gardens. A few species, such as A. purpurascens, appear to require partial shade.
Harvest and Storage of Milkweed Seeds
The timing of the collection of milkweed pods or seeds is critical. Mature pods are those that are within a day or two of opening. If you squeeze the pods and they don’t open easily, they usually do not contain mature brown seeds. Seeds well into the process of browning and hardening will germinate when planted the next season. Pale or white seeds should be not collected. Freshly collected pods dry should be dried in an open area with good air circulation. Once the pods are thoroughly dry, the seeds can be separated from the coma, or silk-like ballooning material, by hand. Separation of seeds can also be accomplished by stripping the seeds and coma from the pods into a paper bag. Shake the contents of the bag vigorously to separate the seeds from the coma and then cut a small hole in a corner of the bottom of the bag and shake out the seeds. Store dried seeds in a cool, dry place protected from mice and insects – a plastic bag (reclosable) or other container in the refrigerator works well.
Stratification
Seeds of most temperate plants need to be stratified, which is a fancy way of saying that they need cold treatment. To stratify seeds, place them in cold, moist potting soil (sterilized soil is best but is not required) in a dark place for several weeks or months. Since most people prefer not to place potting soil in their refrigerators, an alternative is to place the seeds between moist paper towels in a plastic bag. This procedure works well, in part because there are fewer fungi and bacteria available to attack the seeds. After a stratification period of 3-6 weeks, the seeds can be planted in warm (70˚F), moist soil. Without stratification, the percentage of seeds that germinate is usually low. Seeds from the tropical milkweed, Asclepias curassavica (and other tropical milkweed species) do not require this treatment. “Shocking” seeds that have been refrigerated by soaking them in warm water for 24 hours also seems to improve germination rates.
Heat Shocking
If you have the time, cold treatment is the way to go but if you are short on time, heat shocking the seeds is another (though typically less reliable) method to increase germination rates of milkweed seeds. To heat shock the seeds, soak them in hot (120-130F) tap water for 12 hours, then drain and repeat three (3) times. Place the seeds in a plastic bag wrapped in a warm, damp paper towel for 24 hours.
Scarification
Even after stratification, seeds of many plant species will not germinate. In these cases, the seed coats appear to require action by physical or chemical agents to break down or abrade the seed coat. “Scarification” with some type of physical abrasion that breaks the seed coat usually works and can be accomplished by placing the seeds in a container with coarse sand and shaking the container for a 30 seconds or so. Scarification may be required for some milkweeds (e.g., A. viridiflora and A. latifolia) and might improve the germination rates of other species.

Planting and Care of Milkweed Plants

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As reported in The Monarch Newsletter, an experiment was conducted to determine the effects of transplanting, fertilizing, and light on milkweed plants.

Milkweed seeds were planted in 4-inch pots, 4-5 seeds per pot, in early Spring. By the end of May, the plants were about 6 inches high. The following tests were conducted:

  • Transferring to 1-gallon containers vs. keeping in 4-inch pots
  • Fertilizing every week, every other week, or water only
  • Plants were kept either:
    • In containers, in maximum sun or partial shade on a patio, or indoors
    • In the ground in a sunny location

After one month, the following observations were made:

  • Transplanting into 1-gallon containers and fertilizing resulted in taller, bushier plants with bigger leaves.
  • Fertilized plants were greener than non-fertilized plants, though weekly fertilizing was not much different from fertilizing every other week for the container plants.
  • There was not much difference whether 1 or 2 of the 4-inch pots were transferred into a 1-gallon container.
  • Plants in full sun grew faster than plants in partial shade.
  • Plants left in small pots benefitted from weekly fertilizing.
  • Indoor plants were bigger as a result of fertilizing, but the plants were softer, thinner, and had very green leaves compared to the outdoor plants, which were tougher. The indoor plants were infested with yellow aphids and a few whiteflies. The outdoor plants were virtually free of pests.
  • Plants in the ground were healthy, but varied considerably in size.

Milkweed is crucial to the Monarch Butterfly. Here are some sources to get you started with adding this beautiful plant to your butterfly-friendly garden:

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