Milkweed plants used to fill North America’s fields, swamps, and grasslands. These tall, graceful, fascinating flowers grow well in disturbed soil, and sprung up in wheat and corn fields across the country. They’re also Monarch butterflies’ favorite foods! If you’d like to know how to grow milkweed plants to help these beneficial pollinators thrive, read on.
A few decades ago, with more powerful herbicides coming into vogue, farm and fields became desolate. They still grow wheat and corn, but the filler plants—the “weeds”—are gone.
Plants like poppies, cornflowers, and milkweed just don’t grow wild in farmers’ fields anymore.
For those of us who love bees and butterflies, this is devastating news. Monarch butterflies especially are suffering. These beautiful butterflies feed exclusively on milkweed as caterpillars.
Naturally, one of the best ways to support the struggling Monarch butterfly population is by growing milkweed in your garden.
Which Milkweed Should I Grow?
There are so many milkweed varieties to choose from. Which milkweed you choose to grow depends a lot on where you live.
Northeast & Midwest
Common Milkweed (Asclepias syriaca) is the best choice for New England’s long winters and rocky fields.
Swamp milkweed (Asclepias incarnata) is perfect in wetlands or bright, garden pots. It can tolerate both very wet and very dry soil conditions.
Butterfly weed (Asclepias tuberosa), also known as “pleurisy root”, grows beautifully in southern climates. Its bright orange flowers attract bees, butterflies, and hummingbirds.
Swamp milkweed grows well in the south as well.
West & Southwest
Showy Milkweed (Asclepias speciosa) and Arizona Milkweed (Asclepias angustifolia) are hardy at high altitudes, and in the western regions’ dry conditions.
Don’t Choose The Wrong Variety
Tropical milkweed is beautiful. It’s also problematic if you’re growing this plant to help preserve Monarch populations. Avoid planting tropical milkweed as a perennial, since this plant doesn’t die back as others do.
If Monarchs lay their eggs at the wrong time, the eggs hatch infested with a parasite. Tropical milkweed (Asclepias curassavica), is pretty and easy to find, but keep it as an annual or grow it indoors. This cultivar doesn’t belong in your butterfly garden.
How to Grow Milkweed Plants
Milkweed has a reputation for being difficult to start from seed. Take heart though: once established, milkweed can spread like, well, a weed.
If you’ve ordered a packet of milkweed seeds, or preserved a pod from last autumn, and felt overwhelmed by all the information about cold stratification, don’t worry! You don’t actually have to stick your damp seeds in the refrigerator for 6 weeks.
Cold stratification just means that milkweed likes to sit somewhere cold for a while before sprouting. So plant your seeds in the late fall. Pick a time before the ground is frozen, but after a couple hard frosts. Around here, the ideal time is mid to late October.
If you’re planting milkweed seeds in spring, you will want to wrap the seeds in damp paper towel and chill them. Anywhere from 3 weeks to 2 months is fine. After the chilling process, you can plant just as you would in the fall.
Preparing the Soil
Clear and loosen the soil in a sunny spot of the garden. Milkweed can handle a little shade, but definitely prefers the sun. This flower loves disturbed soil, which is why it grows so happily in plowed fields.
Don’t worry too much about the quality of the soil. Milkweed is a hardy plant. While it prefers loose, well-drained soil, it can grow easily in clay or sandy soil as well.
Before planting your seeds, drench the soil with water. Don’t just moisten the soil: really douse it with water. You want your soil to be saturated before planting milkweed seeds.
Planting the Seeds
When the soil is wet, plant the seeds about an inch deep. You don’t have to measure perfectly: just poke your index finger into the soil up to the first knuckle and pop in a seed. Space the seeds about 6-7 inches apart.
Remember though, that over the winter the ground shifts and your seeds will move around a bit. As a result, they won’t all come up exactly where you planted them. Milkweed seeds have a relatively good germination rate when cold stratified, but expect a few of your seeds to fail.
Cover your seeds with damp soil. You can bed it down with a bit of mulch as well to keep the area from drying out.
Now, since you’ll be waiting all winter for your seeds to sprout, you may want to mark the spot with some durable plant labels. We like to tie a little flags on top of short saplings to mark either end of the bed. If you don’t tend to have multiple feet of snow, you may prefer something shorter and more specific.
Your seeds will sprout in the spring, when the snow is gone and the ground is warm and workable again. They will probably need some extra spacing in the spring, but give them a month or two of growth before spacing them out.
Most young milkweed plants will need about a foot of space between them to allow for healthy growth. They can grow anywhere from 2 to 6 feet in height, so don’t crowd them. You can easily crowded young seedlings to extend your milkweed bed.
Once sprouted, milkweed thrives on neglect. It can survive heavy rains, extended droughts, and long cloudy seasons. During long droughts, if you want to keep the flowers blooming, water up to twice a week. Otherwise, leave this wild plant to grow and spread as it chooses.
Save the Milkweed for the Butterflies!
Milkweed is a tough, disease-resistant plant, but it can attract an undesirable element. Slugs and aphids can become a problem. They want to eat all the milkweed leaves and leave nothing for the caterpillars.
They must be stopped.
Slugs are drawn to milkweed leaves. These slimy, slow-moving pests can devastate your plants if left unchecked. In especially bad slug seasons, I like to walk through the garden with a salt cellar, sprinkling the little monsters as I go.
Salt will dissolve your slugs, but it’s a pretty gross process. Beer traps are also effective, and they require less consistent effort. Just bury a few empty tin cans in the ground, with just the lip sticking up above the soil. Fill them with beer, and leave them out for a few weeks.
Slugs love beer. They flock to the traps, fall in, and drown. It’s an easy solution. Just remember to clean out and reset your traps every few weeks.
These greedy little insects like to suck out the leaves’ milky sap. They’re often kept in check by their own, natural predators, but can sometimes get out of hand. If you have an aphid infestation, mix up a batch of insecticidal soap and spray them down.
The soap will kill the aphids, but be careful. Check your milkweed for Monarch eggs first. Insecticidal soap will kill those eggs as well as the aphids. Before you spray, collect the eggs for in-home hatching, or just avoid spraying directly on leaves with eggs attached.
Monarch eggs are white. There is generally only one egg under each leaf on your milkweed plant. Milkweed aphids, on the other hand, are yellow and live in clustered colonies.
Harvesting milkweed seeds can be a challenge. The seeds form in pods with piles of soft fluff, which then burst when the seeds are ready to sow. It’s a big, fluffy, white mess. The problem is that if you harvest the seeds too soon, they’re not viable.
So, how do you collect healthy, viable milkweed seeds before the pods scatter them to the winds? There are two great options:
Rubber Band It!
When the pods are formed, but not yet ripe, gently secure a rubber band around each one. Now wait and watch. You’ll see the pod start to split along the edges. When this happens, your pod is ready to harvest.
The rubber band holds it together until you’ve got it somewhere contained. I like to put the pods in a paper bag, remove the rubber bands, and then sift through the fluff to find the seeds. Everything stays together this way, and you avoid wasting a lot of seeds.
Bag It Up
You know those pretty, cloth gift bags? Pick a few of the breathable ones: organza or muslin work best. Now fit them over the pods and tie them shut around the stems. When the pod bursts, it’ll be entirely contained in the bag.
This is a great option if you’re planning to give away milkweed seeds to friends and neighbors. When the pod has burst, just remove the whole bag from the plant. You can gently shake out the pod and clear out some fluff before gifting, or not. Either way, you and your family will have plenty of milkweed seeds to plant.
Ready to get started? I know I am. This fall (or spring), plunk some seeds down in the soil and see what happens. I think you’ll end up with a bed of lovely, tall milkweed plants and a beautiful butterfly garden.
Let’s get started!