- Growing Milkweed – Using The Milkweed Plant In The Garden
- The Milkweed Flower
- How to Grow Milkweed Plants
- Growing Milkweed Seeds
- The monarch butterfly host plant: Milkweeds and how to grow them from seed
- What’s So Special About Milkweed?
- Monarch Butterfly Host Plant Species
- 6 Favorite Perennial Milkweed Species for Monarch Butterflies:
- How to Grow Perennial Milkweeds from Seed
- How to Plant Milkweed Seeds
- Artificial Stratification
- Birds and Monarchs
- Harvest Milkweed Seed
- Learn How To Plant, Care and Grow Splendid Asclepias
- Finding, Collecting, and Growing Milkweed
- Question and Answer
- How can I grow milkweed from seed?
- Habitat at Home: Growing Milkweed
Growing Milkweed – Using The Milkweed Plant In The Garden
The milkweed plant may be considered a weed and banished from the garden by those unaware of its special traits. True, it may be found growing along roadsides and in ditches and may require removal from commercial fields. However, the reason for planting milkweed in the garden flies by in summer and enchants most who see them: Monarch butterflies.
The Milkweed Flower
The milkweed flower (Asclepias syriaca) and its cousin butterfly weed (Asclepias tuberosa) are an integral part of the butterfly garden, a source of nectar for butterflies and hummingbirds. Growing milkweed supplies larvae of the Monarch with food and shelter, providing caterpillars food and a resting place before they leave the caterpillar stage and become butterflies. As the plants can be toxic; consumption of the plant protects caterpillars from predators.
Historically, the milkweed plant was valuable when grown for its medicinal properties. Today the silky material attached to its numerous seeds is sometimes used for filling in lifejackets. Seeds are contained in an attractive pod that bursts and sends seeds drifting through the air, borne by wind. This is a reason to remove seed pods when you grow milkweed plants.
How to Grow Milkweed Plants
You can easily grow milkweed plants to attract the Monarch and other flying creatures to your garden. Plant seeds of the milkweed plant indoors or direct sow outside after danger of frost has passed and soil has warmed. If the appearance of the plant is too weedy for your taste, grow milkweed plants in a hidden but sunny corner or at the back of a border.
This may lead you to wonder what does milkweed look like. The milkweed plant is an upright specimen that may reach 2 to 6 feet. Leaves grow from a thick stalk and are large and green, taking on a reddish color as the plant matures. In youth, leaves are waxy, pointed and dark green, later dropping from the stem and allowing the milky substance to exude from the growing milkweed. Stems become hollow and hairy as the plant matures. The milkweed flower is pink to purple to orange and blooms from June to August.
Growing Milkweed Seeds
Milkweed often does not begin growing in northern gardens in time to be fully beneficial to butterflies. There you can start seeds of milkweed inside so they will be ready to plant when the soil has warmed.
Milkweed plants benefit from vernalization, a process of cold treatment, before sprouting. They get this when planted outside, but to speed up the growing process, treat the seeds through stratification. Place seeds into a container of moist soil, cover with a plastic bag and refrigerate for at least three weeks. Plant into containers, if desired, and place under a grow light inside about six weeks before soil temperatures outside have warmed. Keep the soil moist by misting, but seeds can rot if allowed to sit in soggy soil.
When plants have two sets of leaves, transplant the seedlings to their permanent, sunny location outside. Space plants about 2 feet apart, if planting in a row. The milkweed plant grows from a long taproot and does not like to be moved after planting outdoors. Mulch can help conserve water.
Grow milkweed plants in mixed borders, meadows and natural areas. Grow milkweed plants with tubular-shaped, shorter flowers in front of them to offer more pollen to our flying friends.
The monarch butterfly host plant: Milkweeds and how to grow them from seed
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Winter doesn’t necessarily seem like the best time to be starting seeds outdoors in most of North America, but for one very valuable group of plants – the milkweeds – winter is the perfect time to get planting. In case you aren’t familiar with this particular group of plants, milkweeds are in the genus Asclepias, and they are the sole monarch butterfly host plant. Before we dive into how to grow these wonderful plants from seed, let me introduce you to some of the very best milkweed species for monarchs.
What’s So Special About Milkweed?
While many species of butterflies have specific host plants they need to raise their young (you can see a list of other butterfly host plants here), no butterfly is more precious to our collective psyche than the monarch. Monarch populations have dropped dramatically the past few decades, and more and more home gardeners want to help by including the monarch butterfly host plant in their garden.
This monarch caterpillar is feasting on the leaves of a species of milkweed known as butterfly weed.
Monarchs co-evolved with milkweeds, and as they did, these butterflies developed a unique adaptation that allows their caterpillars to feed on a plant that many other insects cannot. You see, the latex-based sap produced by milkweed plants contains toxic compounds called cardenolides. Most other insects, save for a handful of species, can’t digest these toxins; it kills them or they avoid it all together due to its foul taste. But monarch caterpillars actually absorb these toxins as they feed on milkweed leaves, rendering the caterpillars themselves toxic to potential predators. The toxins found in the monarch butterfly host plant actually help protect the caterpillars and adult butterflies from birds and other predators.
Here’s a cool video of our Jessica Walliser discovering tiny monarch caterpillars on the milkweed in her own backyard.
Related post: How to Grow a Caterpillar Garden
Monarch Butterfly Host Plant Species
Despite milkweed’s status as the only monarch butterfly host plant, there are many different species of milkweeds that monarchs can use to raise their young. While some species have been found to be preferred over others, all members of the genus Asclepias can be used as a monarch butterfly host plant.
This female monarch is busy laying eggs on the leaves of common milkweed.
When planting milkweed in your garden, it’s important to choose a species of milkweed that’s native to your region whenever possible. Thankfully, there are several milkweed species that have a broad native range and are suitable for planting across much of North America. As we dive into the following list of my favorite varieties of perennial milkweed, know that these particular species are good for most parts of the continent. I am not including the annual known as tropical milkweed (Asclepias curassavica) on my list because it is a plant that’s much debated. There’s evidence that it negatively impacts monarch health and migration in some parts of the country. Plus, it isn’t perennial, nor is it native to the U.S. or Canada.
Monarch eggs are tiny and difficult to spot. Check the leaves carefully for the leaves.
6 Favorite Perennial Milkweed Species for Monarch Butterflies:
Swamp Milkweed (Asclepias incarnata): Don’t let the common name of this milkweed fool you. Just because “swamp” is in the name, doesn’t mean this species of milkweed requires wet conditions. In fact, swamp milkweed does grow in saturated soils, but it also grows just fine in well-drained garden soil. It’s clump forming, so unlike some other milkweed species, it doesn’t take over the garden with spreading roots (common milkweed, I’m talking about you!). I have many clumps of swamp milkweed in my Pennsylvania garden, and I’ve found it to be the easiest species to grow (see the section at the end of this article for info on how to grow milkweeds from seed). Plant this monarch butterfly host plant in full to part sun. It grows about four feet tall and is hardy in zones 3 to 7. You can buy seeds of swamp milkweed here.
Swamp milkweed is a great clump former with beautiful, deep pink flowers.
Common Milkweed (Asclepias syriaca): Common milkweed was once an ubiquitous roadside weed, but with the increased use of herbicides, it’s not so common anymore. The large, round globes of common milkweed flowers are a favorite of many pollinators, and its broad leaves always play host to many monarch caterpillars in my own backyard. But, this plant comes with a warning: It is an extremely aggressive spreader, forming large colonies that spread not just by seed, but also by underground roots called rhizomes. You’ll want to give common milkweed plenty of room. It’s hardy from zones 3-9 and reaches up to 6 feet in height. You can buy seeds of common milkweed here.
Common milkweed is one of the easiest milkweeds to grow, but it can be aggressive in the garden.
Purple Milkweed (Asclepias purpurascens): My favorite species of monarch butterfly host plant, purple milkweed is hard to find in the nursery trade but oh so beautiful! With a form similar to common milkweed, purple milkweed is a stand out primarily due to the color of its flowers. Best described as brilliant pink, the blooms of this species of monarch butterfly host plant are absolutely stunning. In the summer, the flowers are alive with many different pollinators, including many native bees. It also spreads by rhizomes, but not quite as aggressively as common milkweed. It’s somewhat difficult to start from seed (see below), but is fully winter hardy in zones 3-8. Seeds can be difficult to find in the trade, so try to find a friend who grows this species and is willing to share seeds.
Purple milkweed is one of many varieties of perennial milkweeds used by monarchs to raise their young.
Butterfly Weed (Asclepias tuberosa): Unlike most other milkweeds, the flowers of butterfly weed are not pink, purple, or white. Instead, this milkweed species has flowers that are bright orange. Its short stature and clump-forming habit make it the perfect fit for most gardens. Though butterfly weed isn’t typically the first milkweed chosen for monarch egg laying, it’s definitely worth growing. Butterfly weed doesn’t like to be transplanted, so starting from seed may prove more fruitful, though it can take years for a plant to go from seed to flower. Hardy in zones 3-9 and reaching just 2 feet in height, the jazzy orange flowers of butterfly weed are nothing short of spectacular. You can buy seeds of butterfly weed here.
Orange flowered butterfly weed is also a milkweed and can serve as a host plant for monarchs.
Showy Milkweed (Asclepias speciosa): Far less aggressive than common milkweed, showy milkweed is an excellent alternative. Hardy in zones 3-9 and reaching about 4 to 5 feet tall, the flower clusters of showy milkweed look like groups of pointed stars. Though there are fewer flowers per cluster than with common milkweed, this monarch butterfly host plant species steals the show with its spiky, pinky-purple blooms. Showy is a great name for it! You can buy seeds of showy milkweed here.
The star-shaped flowers of showy milkweed are so pretty.
Whorled Milkweed (Asclepias verticillata): The slender, needle-like leaves of this monarch butterfly host plant don’t look like many other milkweeds out there. The plant has a soft, feathery appearance, and since it tops out at about 3 feet in height, it makes a great addition to a perennial border. Whorled milkweed is not an aggressive grower, but it does spread via underground rhizomes, so be prepared to give it lots of room. The flowers of this species are a soft white with just a hint of pink at their centers. Small clusters of flowers top nearly every stem, and despite the delicate appearance of this milkweed species, it can feed a lot of monarch caterpillars. You can buy seed of whorled milkweed here.
There are, of course, many regional species of milkweed as well. We recommend the book The Monarch: Saving Our Most-Loved Butterfly by Kylee Baumle for a full list of over 70 native milkweed species and their geographical ranges.
Related post: A Wildlife Garden Project for All Seasons
How to Grow Perennial Milkweeds from Seed
Now that I’ve introduced you to some of my favorite species of the monarch butterfly host plant, it’s time to get growing! You may recall that at the start of this article I mentioned that winter is the perfect time to plant milkweed seeds. This is because the seeds of perennial milkweed species need to be exposed to an extended period of freezing temperatures in order to break dormancy. The process is known as stratification, and in nature, milkweed seeds naturally pass through this period of cold and wet as winter progresses. So, in order to have success growing milkweed from seed, you have to make sure the seeds are stratified either naturally or artificially.
If you head outdoors and plant perennial milkweed seeds in the spring, you’ll have little to no luck getting them to germinate. Instead, plant the seeds in the late autumn or winter. Here’s how to do it.
Most milkweeds are easy to start from seed, if the seeds are exposed to cold temperatures.
How to Plant Milkweed Seeds
Step 1: Act like Mother Nature. For the best results when growing milkweeds from seed, if you live where winters are cold, simply go outdoors anytime from late fall through mid-winter and drop milkweed seeds wherever you want them in the garden, just like Mother Nature does. Do not cover the seeds! Simply press them against the soil with your hand or the sole of your shoe. Seeds of the monarch butterfly host plant require light to germinate, so if you cover them with soil, they won’t germinate come spring.
Step 2: Walk away. Seriously. That’s it. The easiest way to grow milkweed seeds is to plant them in the fall or winter forget about them. As winter progresses, they’ll naturally be exposed to the eight to ten weeks of cold temperatures required for them to germinate when spring arrives.
Related post: Plant Extra Dill for Swallowtail Butterflies
If you want to support monarch butterflies like this one, you need to plant host plants for the caterpillars.
You can also grow perennial milkweeds from seed by exposing them to an artificial winter. To do this, fold the seeds into a very slightly damp paper towel, and put the towel in a zipper-top baggie. Place the baggie in the back of the fridge for eight to ten weeks, then remove it and sprinkle the seeds into the garden, again being careful not to cover them with soil.
As you can see, milkweeds are both gorgeous and much needed. Grow as many varieties of this monarch butterfly host plant as you can, and we will all reap the benefits.
Each milkweed page indexed below includes a brief description of the species’ range and characteristics as well as thumbnail and full-size images of its leaves, flowers and entire plant. Remember, there are more than 100 species of milkweed, so we need your help in building this guide. If you have access to photos of species not listed here or of those with incomplete or poor image collections, we would love to add your photos and credit your contribution. Just contact us and we’ll figure out the easiest way to get your photos online.
Milkweeds are an excellent choice for a habitat garden. They are a host plant for monarch butterflies and other specialized insects, and a nectar source for many pollinators. Their increasing scarcity in the wild makes them especially welcome in your garden, where patches of (ideally native-to-your-region) milkweeds can act as stepping stones for migrating monarchs; helping them maintain their population as each successive generation flits from backyard to backyard on their journey north and then south again. Below we explain what happened to all the milkweeds in the wild, discuss why they are critical for monarchs, advise on how to choose the correct species of milkweed for your region, and how to join the effort to collect and share seeds.
Photo © Samuel
Did you know there is more than one kind of milkweed? At the big box stores you may find seed or plants of tropical milkweed (Asclepias curassavica) (pictured above), but this is not native to most of N. America (a handful of places in California, Texas, Louisiana, and Florida are the exceptions). Whether or not this tropical species provides a net benefit or loss to the monarch population is a topic of open research.
Clean (Ophryocystis elektroscirrha (OE) infection-free) monarch butterfly scales magnified using a microscope.
Photo © BlueRidgeKitties
Over the summer of 2015, Karen Oberhauser from the University of Minnesota Monarch Lab did a Q&A for folks with questions about monarchs. She says this of the Asclepias curassavica controversy:
Tropical milkweed (Asclepias curassavica) is not native to the United States or Canada. Because it is attractive and easy to grow, it is often the most widely available milkweed at commercial nurseries. Because tropical milkweed historically occurs in the New World tropics, it is adapted to grow year-round, whereas most native North American milkweed species die back each winter. When tropical milkweed is planted in the coastal southern U.S. and California, these plants continue to flower and produce new leaves throughout the fall and winter, except during rare freeze events. Potential negative effects on monarchs include 1) continuous breeding on the same plants, which can lead to a build-up of Ophryocystis elektroscirrha (OE) infection, and 2) availability of milkweed during a time that it is not naturally available, and so potential consequent impacts on monarch breeding during the fall migration. sourceopen_in_new
As her research continues, we will keep our audience posted on her results. Until then, consider a milkweed native to your region which will not require extra water, and will cycle according to the climate (see below for ideas), or cut back your tropical milkweed in the winter months to mitigate build-up of OE spores and stop monarch breeding during fall migration.
Photo © Joshua Mayer
Historically, milkweed has been a common plant throughout the vast prairie regions in the United States. Twenty-nine species of Asclepias, most of them grassland species, are native to the late summer breeding range of the monarch. In all of North America there are over 100 species of milkweeds, showing amazing diversity. Check-out our slide show at the end of this article for a sampling of these colorful, interesting plants.
Photo © Mark’s Postcards from Beloit
As the prairies came under cultivation there was a corresponding increase in the distribution and abundance of Common Milkweed (A. syriaca), which was able to live in and around the corn and soybean crops dominating prairie agricultureopen_in_new.
Photo © USFWSmidwest
As a result, common milkweed, A. syriaca, has been the primary food of monarch butterflies migrating across the agricultural regions. In a sample of 394 overwintering monarch butterflies in Mexico, 382 had fed on the common milkweed as larvaeopen_in_new. This important host species, however, has been losing ground as Roundup-ready corn and soybean have been replacing traditional crops, allowing widespread use of herbicides that target all weeds in agricultural fields, including milkweeds. The resulting decrease in milkweed availability likely accounts for the dramatic decline in monarch populations witnessed over the last 20 years. It is estimated that since 1996, we’ve lost enough milkweed habitat to cover an area the size of Texas (~69 million hectacres)open_in_new.
Photo © JKehoe_Photos
Milkweed is named for its milky sap, which consists of latex-containing alkaloids and several other complex compounds including cardenolides. In the image above, showing a California ladybug larva (not a monarch caterpillar!), the white spots are places where the milkweed’s “milk,” or latex-containing sap, has leaked out as a result of aphid damage. This ladybug larva has likely consumed most of the aphids, and is now preparing to pupate on the underside of the milkweed leaf.
Photo © USFWSmidwest
Most species of milkweed, when ingested, are toxic to animals (vertebrates specifically) due to the cardenolides, plant alkaloids that are also called cardiac glycosides because they can disrupt vertebrate heart function. When caterpillars eat the leaves of the milkweed, they also ingest the plants’ toxins. There is a lot of variation in the amount of cardiac glycosides in different species of milkweeds. As caterpillars eat, these toxic compounds build-up in their bodies, and eventually are found in high concentrations in the wings and exoskeletons of adult butterfliesopen_in_new, making the insects themselves toxic to predators. Caterpillars consume a lot of milkweed leaves in order to gain enough mass in such a short time. Notice, in the image above, the vast difference in sizes between the young caterpillars and those that are just 10 days older. It is estimated that a single monarch caterpillar needs around 20 entire leaves to grow large enough to successfully pupate.
Birds and Monarchs
Photo © Steve Shinn
Did You Know? The story of birds and monarchs is more complicated than you may have learned in school? You’ve probably heard the narrative of how birds learn to avoid brightly-colored monarchs because they taste bitter. In the late 50s Dr. Brower (1958) used captive Florida Scrub-Jays (Aphelocoma coerulescens) to test this hypothesis. Some had monarchs and swallowtails put in their cages, while others were offered viceroys and swallowtails. One group of birds ate all of the swallowtails offered and half of the viceroys. The other group ate all of their swallowtails and not a single monarch. Dr. Brower concluded that monarchs are inedible, and that the viceroy is partially protected by its resemblance to the monarch.
Shining Cuckoo (Chrysococcyx lucidus) holding a monarch caterpillar in New Zealand
Photo © Anna Barnett
The Plot Thickens. Suspecting that the story was more complex, follow-up researchers engaged in a more naturalistic (with wild, rather than caged birds) observational study, because they felt that captive birds do not always behave the way wilds ones do. Here is how they summarize their research:
In the summer of 1963, five species were frequent visitors; cardinals, brown thrashers, grackles, robins, and english sparrows. They were fed on table scraps of every sort, birdseed, and suet. A white enamel pan was placed on the ground in this yard between the birdbath and one of the feeders. Live (and lively) monarch butterflies, after having their wings trimmed… were placed in the pan every morning before dawn. …and they did elicit a feeding response in the birds. Nearly every morning for two weeks the birds emptied the pan. The best customers were the brown thrashers, one pair of which was observed feeding the butterflies to their young. Between July 18 and July 31, 110 of 112 … monarchs were eaten. The birds that ate them could have lived off a bounteous Iowa summer, or the food in the bird feeders if monarchs were distasteful to them. sourceopen_in_new
In overwintering grounds in Mexico, two species of birds are well-known for preying on monarchs: Black-backed Orioles and Black-headed Grosbeaksopen_in_new. At overwintering sites in California researchers have observed Chestnut-backed Chickadees (Poecile rufescens), European Starlings (Sturnus vulgaris), Western Scrub-Jays (Aphelocoma californica), and California Towhee (Pipilo crissalis) eating monarchs. All of these birds have different strategies for coping with the toxic compounds in their bodies, ranging from eating the parts of the insect with less toxins, to taking extended feeding breaks. Photo © John Flannery
Milkweeds are also important as a source of nectar to many pollinators. In the image above, see how many swallowtails you can spot (most are spicebush swallowtails) on this lovely milkweed commonly called Butterfly weed (A. tuberosa). By planting milkweeds, you aren’t just providing a host plant for monarchs, but a great pollinator plant in general.
Photo © a2gemma
Milkweeds are perennial plants, living for several years and regrowing each spring from rootstock, not just from seed, like annuals. The young, regrowing milkweeds in the image to the left are strong robust plants even early in the Spring, because of their perennial habit. These plants (likely growing from the same colonial restock) are clones. Both will grow-up to produce seed late in the Fall.
Photo © USFWS South East Region
If you want to help with the declining monarch population, you can do several things. Plant milkweeds, harvest and share milkweed seeds, advocate that ditches and medians not be mowed regularly (they are important wild spaces for milkweed), and refrain from using pesticides in your yard. Check out this cool species map to find your region’s milkweeds. Then use the Milkweed Market to find the appropriate kind of milkweed seed for your area.
Harvest Milkweed Seed
Photo © Helena Jacoba
Harvesting milkweed seed, either for personal use or to donate to a seed-saving service, is an excellent way to help. Check-out this wonderful seed-harvesting tutorial over at Monarch Butterfly Garden to learn how. Late fall is a great time to get out there and harvest. To donate your seeds, or request seeds native to your region to plant on your own property, check out Monarch Watch’s donation program. It is a really neat way people like you are making native seeds accessible.
Learn How To Plant, Care and Grow Splendid Asclepias
Mostly native to the U.S. and Canada, Asclepias include over 100 species of evergreen or deciduous perennials adorned with clusters of small, interestingly shaped blooms that are irresistible to butterflies. Attractive and easy to grow, they shine in many perennial gardens and are a key component of butterfly gardens, cottage gardens, or prairies and meadows.
Often fragrant, the attractive flowers are a great source of nectar for butterflies, hummingbirds, bees, and other beneficial insects. Milkweed plants are critical to the monarch butterflies survival. Without Milkweed, monarchs cannot successfully reproduce and the species declines. In the last 20 years, the monarch butterfly population in North America has decreased by 90%. By planting milkweed in your own garden, you can help reverse the fortune of these beautiful insects!
1. Select The Right Site
- Best flowering usually occurs in full sun except for a few species such as Asclepias purpurascens (Purple Milkweed), which prefers partial shade.
- Soil conditions vary with the Milkweed variety. While light, well-drained soils are usually best, some species including Asclepia incarnata (Swamp Milkweed) and Asclepia sullivantii (Prairie Milkweed) thrive in moist conditions.
2. Planting Milkweed
- Potted plants: plant them directly into the garden in spring after the danger of frost has passed.
- Seeds: plant your seeds directly into the soil in the fall. As an alternative, you can start your seeds indoors, 4-8 weeks before the average date of last frost. Use plastic flats or seedling trays. Fill them 3/4 with potting soil, scatter the seeds on the soil surface 1/2 in. apart (1 cm). Cover with 1/4 in. (0.5 cm) of soil mix. Water thoroughly and place them either in a sunny window or directly under the grow lights. Most seeds will germinate in 7-10 days if the flats are maintained at 75˚F (24˚C). After the seeds have germinated and are 3-6 in. tall, they are ready to be transplanted into your garden.
- Loosen the soil where you will be planting.
- Plant your seedlings 6-24 in. apart (15-60 cm) depending on the species. Water regularly. Add mulch around the seedlings to hold in the moisture and minimizes the growth of competing weeds.
- Asclepia incarnata (Swamp Milkweed) needs evenly moist soils. Most other Milkweed species are suited to a dry environment.
- No fertilization needed.
- No division required.
- To avoid unwanted seedlings, remove all seed pods in early fall, before they split open and spread their seed.
Finding, Collecting, and Growing Milkweed
Finding and Collecting Milkweed
Common milkweed, A. syriaca, growing at a park in Minnesota. (Photo: Wendy Caldwell)
Most milkweed species grow particularly well in disturbed areas, so start by looking in the following places: roadsides, pastures, along railroad tracks, bike paths, highway medians, agricultural field margins, vacant land, cultivated gardens, and parks.
When collecting milkweed foliage to feed to caterpillars, it is best to pick the entire plant (check for other invertebrates first to ensure that you don’t take any unexpected critters home with you). You can pick several days worth of milkweed and keep it in a plastic bag in the refrigerator. Wash it in water before using it. Milkweed stays fresher if you keep the end moist by wrapping it in a wet paper towel and then covering it with aluminum foil, or use florist water tubes or soda bottles. Potted plants can also be purchased from your local nursery, but make sure that they have not been treated with systemic insecticides before feeding them to your monarchs (ask the grower if you aren’t sure).
If you plan to grow your own milkweeds, or add milkweeds to your current site, you can collect seeds when the milkweed pods are ready to burst (this occurs in the fall in the northern U.S.). Once you have collected seeds, remove them from the pods and store them in an airtight container in a cool and dry environment (such as a basement or garage) until you are ready to use them. It is best to include a moisture remover (i.e. Silica gel) in your seed storage container. If the seeds are moist for a long period of time, they will start to rot and eventually die. Seeds collected in the Northern US will not germinate without cold stratification.
Milkweed being cultivated in a greenhouse (Photo: Chip Taylor)
Most seeds of temperate plants should be vernalized (cold treated); this ensures a higher germination rate than if seeds are sowed without this pre-treatment. Many of the southern species, such as tropical milkweed, will grow without cold-treatment. The most successful means of milkweed vernalization is through stratification. By stratifying, or subjecting seeds to a cold/moist environment for a short period of time, you simulate the conditions of a seed’s natural break of dormancy that occurs when the seeds spend the winter in the ground. To stratify, first obtain a substrate. Peat has been found to produce the best results, in addition, peat/clay also work well. Secondly, moisten the substrate with water and place the seeds in the cold soil. Store the seeds in a dark place (a refrigerator crisper works well) with a temperature of approximately 5°C for a minimum of 3 weeks up to 3 months.
To allow for natural stratification, sow collected seeds directly into a mulched bed in the fall and the seed will germinate the following spring.
If you have grow lights or a greenhouse, it is best to start your milkweed seeds indoors a couple of months before you are able to transplant them outdoors. We fill the seedling trays approximately ¾ with potting soil (light, well-drained soils work best for most species) and scatter 3-4 seeds per cup and then cover the seeds with an additional ¼ inch of soil. The soil is then fully saturated with water and placed either in a sunny window or directly under the grow lights; they need a lot of light and warmth to germinate and grow. It’s best to keep the temperature at 26/24°C day/night with a 16-hour photo phase. Keep the soil moist, but don’t overdo it. If the seedlings are too wet, fungal growth can occur and kill the seedlings. The seeds will take approximately 10 days to germinate. Once there are 4 true leaves on the seedlings (the seedlings will be approximately 3 inches tall), the plants can be transplanted into your garden. Most milkweed species do best in full sunlight, so choose an open area with lots of sun. Plant the seedlings 1-2 feet apart. The seedlings should be watered frequently; mulch can be used to help hold in the moisture around the plants.
For indoor use, plant the seeds just beneath the soil surface using a rather deep pot, as they have a long taproot. Once the plants are in the seedling stage, fertilize once a week. To encourage fullness and more leaves, you can pinch off the top set of leaves (when there are at least two sets of leaves) to promote branching. It takes at least a month for the plant to be ready for the larvae to eat. Once the plant is big enough, you can simply place the entire plant, pot and all, into the cage. After the larvae have eaten the leaves, simply cut the plant off about two inches above the soil and new shoots will grow in 3-4 weeks.
When planting seed outdoors, keep in mind that all plants have optimal soil temperatures for germination, which makes propagation a little more difficult. It is best to plant the seeds as early as possible, but make sure that you plant after the last frost.
- Next: Catching Butterflies “
Milkweed for Butterflies
Monarch caterpillars ONLY eat milkweed. In fact, the monarch butterfly is also known as the “milkweed butterfly.”
The milkweed plant provides all the nourishment the monarch needs to transform the Monarch caterpillar into the adult butterfly.
But these plants are rapidly disappearing, due to the loss of habitat stemming from land development and the widespread spraying of weed killer on the fields where they live.
It’s easy to grow your own Milkweed!
There are many varieties of milkweed. There are some which thrive in full sun, in humid conditions and even in very dry conditions. As a perennial, they will come back every year, despite harsh winter conditions. They typically bloom rosy pink flowers, and are the preferred host plant for the monarch butterfly. To find out more about the various species of milkweed and which are best for your area, check out this factsheet courtesy of Monarch Joint Venture.
IMPORTANT NOTE: The species of milkweed we offer is Asclepias syriaca. Planting this variety of seed in a dry sandy location, particularly in the southwest United States, will not produce a successful planting.
Question and Answer
How can I grow milkweed from seed?
Milkweed seed can be planted directly in soil, or started indoors. You can sow milkweed seeds by scattering them on the soil surface 1/4-1/2 inch apart, and then cover them with about 1/4 inch of additional soil. Water the area frequently after planting until plants become established. Many species need to be vernalized (cold treated) before planting. Vernalized seeds can be planted in the spring after the danger of frost has passed. Non-vernalized seeds can be planted in the fall, and nature will provide the cold treatment. See Monarch Watch’s milkweed propagation guide for further recommendations, information on vernalization and instructions for starting milkweed seeds indoors. Also watch our Monarch Conservation Webinar: Growing Milkweed for Monarch Conservation (scroll down to May 2016) to hear from Chip Taylor of Monarch Watch on milkweed growing techniques and best practices. For further details on milkweed growing and conservation use, visit the Xerces Society’s Milkweed Practicitoner Guide, which is a complete guide to milkweeds, including biology/ecology, propagation, benefits to wildlife, and use in restoration projects.
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Habitat at Home: Growing Milkweed
Monarch on common milkweed
Growing native milkweed in your yard can create wonderful habitat for all kinds of native insects, especially the monarch butterfly! In fact, monarchs need milkweed to survive. Adult monarchs lay their eggs exclusively on milkweed leaves, nowhere else! In this month’s Habitat at Home we will give you some tips for growing milkweed from seed, so that you might see some monarchs in your backyard.
To make sure you get the best info on how to grow milkweed in your backyard we talked to Kim Bailey, owner of Milkweed Meadows Farm in Fruitland, NC. Kim is an expert on all things milkweed and monarch, even supplying local schools with monarch eggs to raise and release. Kim also supplies milkweed seeds to Sow True Seeds – a great place to get native milkweed seeds. Lets get started!
Choose your milkweed variety! Sow True Seeds offers a few types, so choose the milkweed that best suits your yard.
Common milkweed – Kim calls this variety exuberant; “It won’t come up in the same spot, but it will pop up a few feet away – with friends!” Because common milkweed tends to spread, it is best for a larger garden or meadow where you don’t mind extra plants popping up. Seeds require cold moist stratification. (See more on that below.)
Swamp milkweed – Swamp milkweed can tolerate extra water, but does well in average soil. This variety is better for smaller gardens and raised beds because it is a perennial and will grow in the same spot each year. Seeds require cold moist stratification.
Butterfly weed – This variety tolerates dry soil the best, making it ideal for raised beds. Butterfly weed is a perennial, and Kim recommends planting this variety somewhere you want it to stay – it can be hard to dig up later. This variety does not require cold moist stratification—seeds can be sown right from the packet!
Butterfly weed is a variety of milkweed.
After choosing your variety, figure out the date you want to plant outdoors and back up about 8 weeks to account for stratification and germination. Kim says the saying “don’t plant your tomatoes until after Mother’s Day” holds true for milkweed as well. Aim to plant your ‘baby’ milkweed outside around mid May or later.
Cold, moist stratification. This is essential! Cold, moist stratification is essentially tricking your seeds into thinking winter has come and gone. You will do this by placing the seeds in either damp vermiculite or damp paper towel (Kim says these work about the same) and into the refrigerator for about 4 weeks. “The seeds need to experience winter, or they don’t think spring is here yet and they will not germinate,” Kim says. “Typically you will see this called cold stratification, but it needs to be moist, too.”
After 4 weeks or more in the fridge, your seeds are ready to sow. If it is later in the season and the chance for frost has passed, you can sow seeds outdoors. If there is still a chance for frost, you can germinate seeds inside and grow using fluorescent or LED lights. Seeds can be grown in most potting soil. Wet the soil and allow it to drain before scattering seeds and covering with about 1/4 inch of soil.
When your milkweed has reached 3-6 inches, it is ready to be planted outdoors! Generally, milkweed prefers full sun. Kim suggests planting a patch, but space them out so it is harder for pests to spread.
To show how cold, moist stratification is used to germinate milkweed seeds, Kim wrote an in-depth blog post for Sow True Seed called The Great Milkweed Germination Test. She also gives step by step instructions on how to take your milkweed seeds from “packet to plant”!
The Great Milkweed Germination Test
Torry Nergart releases monarch butterflies, which got their start as eggs laid on milkweed in the pollinator garden at our office.
What’s On My Milkweed?!
You might find some curiosities on your milkweed once it is growing outside. Here’s what they might be:
- Monarch eggs – Monarch eggs are tiny, white, and conical. Monarch butterflies will typically lay 1 egg per milkweed plant, so the caterpillar will have less competition for food as it grows. Can you spot the tiny monarch eggs Kim found on her milkweed?
- Praying mantis ootheca – Ootheca is is just a fancy word for egg sac! These can be off-white to brown and look like a foamy blob on the stem of a plant. Leave these be – praying mantis will eat all kinds of backyard pests!
- Aphids – these clusters of yellow, orange, or green insects look a little bit like insect eggs, but don’t be fooled! Kim says some aphids are fine, but if there are too many you can rinse them off with water.
- Ladybug larvae – These spiked black and red larvae look almost nothing like a lady bug, but that’s what they will become! If you have aphids, hopefully you have these. Ladybugs and their larvae love to eat aphids.
Habitat at Home is a monthly feature dedicated to providing you with tips to make your yard and home a better habitat for native plants, animals, and insects. Written by Kelly Holland.
Tags: Education, Habitat at Home