Milkweeds (Asclepsias) are native to North America, with more than a hundred species found in the US and Canada. The irritating, sticky white sap for which milkweed is named just happens to be vital to the monarch butterfly’s lifecycle. By ingesting it, they use toxins found in the sap to repel predators, creating a natural defense system.
As the sole host plant for monarchs, milkweeds provide the growing larvae with food as well as sap. Adults also feed on milkweed nectar. Without these critical plants, monarchs would have nowhere to lay their eggs, and their species would soon cease to exist.
Already, monarch numbers are in steep decline. Prior to 1997 estimates put their population at 1.2 million. By 2017, it had plummeted to under 200,000. Today, the Western migration especially is in trouble.
To help offset the loss of milkweeds from roadsides, fields and hedgerows, there are initiatives underway all over the country to replant milkweed through private, nonprofit and community restoration projects. That’s why it’s so critical we gardeners do our part and plant milkweed in gardens, open spaces and meadows.
In the Northeast, there are three milkweed species that are readily available and several lesser-known ones. You’re probably familiar with at least two of them. Other species do best in the dry, arid climates of the West and Southwest, and aren’t suitable here.
One exception you might want to try is the Showy milkweed, native to California. Of course this is Pennsylvania, so it’s out of its element here. That said, I’ve grown it for two seasons so far, although it did struggle last summer after succumbing to severe mildew. We’ll see if it makes it in 2022. Pollinators love it.
The Xerces Society recommends five species for the Northeast:
Common milkweed (Asclepias syriaca) This is the tall, 3- to 5-foot robust wildflower everyone knows. It’s also divinely fragrant when it first opens and it will perfume the whole garden. It needs space where it can ramble, so don’t put it in a tidy flowerbed. The foliage is large and coarse; unfortunately it usually turns ragged as the season progresses. I used to grow it in a naturalized area at a former property.
This plant spreads aggressively by underground rhizome “runners” as well as by seed parachutes; however in a well-mulched area, the runners can be easily pulled up and clipped off, and the seed pods deadheaded before they open. Keep in mind that it can be difficult to control if planted next to the lawn or your neighbor’s property line!
Butterfly weed (Asclepsias tuberosa) The best choice for small gardens and flowerbeds, and widely available. This bright orange native, or the newer “Hello Yellow” cultivar, is well behaved and much shorter at 24″ tall. Foliage is slim and attractive. Stays mostly upright or leans a little, and thrives in full sun. To prevent self-seeding, remove the seed pods when they resemble okra, before they split. May repeat bloom if deadheaded early.
Butterfly weed looks great with both annuals and perennials like marigolds, yarrow, geum, salvia, catmint, rudbeckia, daisies, zinnias, lambs ears and anywhere you want a splash of orange or yellow.
It’s also right at home in open expanses. A few years ago I recall it blooming gloriously in the meadow at Sagamore HIll, the summer home of Teddy Roosevelt in Oyster Bay, New York.
Swamp milkweed (Asclepsias incarnata) A tall, slim 4- to 5-foot milkweed with narrow leaves and pretty, deep pink flowers. While not as fragrant as common milkweed, the scent is light and sweet. I love this cultivar for its unfussy habit and the color it contributes.
This cultivar needs moist, humus-rich soil to thrive. It’s done well for me, and tolerates some shade (with staking). Not invasive at all. Good mildew resistance. A lovely choice with other tall perennials like thalictrum, sunflowers, joe-pyeweed, veronicastrum, ironweed, firetail, queen anne’s lace, and blue sage.
Whorled milkweed – A lesser known, shorter (2′) species that has a nice creamy flower and narrow, whorled leaves. This species spreads by rhizome runners like common milkweed, so it’s best suited for open areas where it can naturalize. Available by mail order.
Poke milkweed – A tall (5′) species for woodlands or mostly shade to full shade. Not invasive at all. Also available from native plant nurseries. I don’t grow this one, but I may try it along the woods.
Showy milkweed (Native to California and Western US) – This tall Western milkweed is dramatic. The exotic-looking flowers bloom in midsummer and look amazing. But after pollination, the silvery foliage gets tattered and ratty-looking, so tuck it in the back somewhere or plant with tall grasses to hide the deteriorating foliage. This plant struggles and flops in our wet climate, but the flowers are so spectacular you may want to try it anyway. The caterpillars love it.
What NOT to plant, or use with caution
Tropical, or Mexican milkweed (Asclepsias currasavica) The Xerces Society is requesting that gardeners forego planting this species. Unlike native milkweeds, Tropical milkweed does not die back where winters are mild, allowing a harmful parasite to overwinter on it. Monarch larvae then ingest the parasite the following year, causing serious deformities, weakened immune systems and increased mortality. Infected larvae sometimes cannot properly unfurl their wings when emerging from their chrysalis and die.
I think this issue is less of a risk here in zone 6, since all milkweeds die off each winter. If you already have this species or want to grow it, make sure you remove and dispose of every last bit of foliage at season’s end. That’s actually good hygiene for all milkweeds.
Growing Milkweed
I’m going to be honest: Milkweeds can be a pain to get established. And a word of caution: when handling any milkweed plant, wear gloves. The sap can be quite irritating if it gets on your skin. Wash it off immediately if you do make contact with it. A quick glance chart can be found at the end of the article.
Butterfly Weed is the easiest to get going, which may or may not produce a few flowers the first year. Of course, if you purchase flowering plants from a nursery, there’s no problem.
Common milkweed usually takes one or two seasons to establish if transplanted as a seedling. (Shoots emerging from a parent rhizome establish much faster since there’s no transplant shock.)
Swamp and Showy milkweeds take at least two years, sometimes a third before flowers appear. So don’t expect much right away if you’re planting seedlings. Just check on them periodically to ensure they’re surviving, and make sure they aren’t getting out-competed.
Site them in full sun or as close to full sun as you can. They’re not picky and will grow in lean or disturbed soils as well as humus. There’s no need to fertilize them, either. Good drainage is helpful.
Swamp milkweed does need moist conditions but despite its name, there’s no need to plant it in a “swampy” place. My swamp milkweed thrives on neglect on my back bank. I do apply a moisture-retentive mulch in spring. These are “plant-it-and-forget-it” perennials, so there’s no need to pamper them.
Aphids
All milkweeds attract hordes of bright orange oleander aphids (an invasive species) where they cluster heavily on the stems and look absolutely gross. However, since monarch larvae and eggs may also be present, it’s not advisable to use chemicals, oils, or jets of water to remove the aphids, because that would also remove any butterfly larvae and eggs. The aphids don’t really harm the milkweed, although their secretions will encourage sooty mold.
You can put on gloves and manually squish them off (ew!) or prune off the worst stems to reduce their number. If you’re sure no butterfly larvae are present, you can carefully treat the plant with an insecticidal soap dilution. Avoid all chemical pesticides, which will leave a residue that can harm pollinators.
Or do as I do… nothing…and try not to look at them!
Butterfly Food
So how do you know when monarch eggs have been laid, or if monarchs are finding your milkweed? Once your plants are at least a foot tall, you can start watching for monarchs to visit them, whether in flower or not. I check my plants regularly when I begin to see monarchs in the area, usually in late May.
Monarch eggs look like small, raised green dots on the undersides of leaves, but they can be hard to spot. I look for the newly hatched baby caterpillars, about a half-inch long, called instars. Their trademark black, white and yellow stripes quickly identify them as monarchs. By the way, plenty of other pollinators visit milkweed too, not just monarchs. At least two species of moths also use it as a host plant.
If your milkweed leaves are looking munched, chances are good there are caterpillars on it somewhere. Often they are hiding underneath the leaves. Caterpillars with other markings are probably moth larvae. It’s not uncommon to find different caterpillars on the same plant. All are beneficial, so leave them be. You can expect to find caterpillars through early fall, although most will be present in June and July here.
Two things to keep in mind:
- Birds often eat the caterpillars before they can mature. Disappointing, yes, but that’s nature doing her thing.
- A caterpillar needs to get almost as big as your little finger before it’s ready to form a chrysalis. Then it often leaves the milkweed plant to find a sturdy stem or branch nearby.
I find old monarch chrysalis husks hanging from daylily leaves and other perennials, but not on the milkweeds themselves. So if you’ve been watching a caterpillar fatten up and it suddenly disappears, don’t assume a bird got it. You might just find it nearby on something else, about one to two feet off the ground, getting ready to pupate.
A Monarch Is Born
A caterpillar hanging upside down in a “J” shape is preparing to form a chrysalis. If you find one in this position, don’t disturb it. Watch it closely over the next few hours! (If you want, mark or stake the spot so you can easily find it later.)
A chrysalis will take about 12 – 14 days to hatch. When it’s close to hatching it will turn transparent, allowing the brightly colored wings to show through. It should hatch the following morning if all goes well.
The Rewards
It’s been such a joy to see monarchs come to my milkweed, lay eggs, watch the larvae feed and finally complete their lifecycle, right in my own garden. Finding a brand-new monarch drying its wings after emergence is very rewarding. If it happens to you I guarantee, you’ll be hooked! There are even backyard butterfly hatching kits you can buy, great fun for kids, grandkids, and adults alike.
So please, think about including milkweed somewhere on your property. Get at least five plants, either the same or different species. Group them together by height, so feeding larvae can easily move from one plant to another. Fewer plants won’t be enough to sustain more than one or two caterpillars to chrysalis stage, and they become very vulnerable to bird predation without ample plant material to hide in.
It’s a great feeling to know you’re helping to conserve these lovely creatures for future generations while also enjoying milkweeds in their own right.
