Growing milkweed for monarchs

Monarch on milkweed ©Janet AllenMonarch on swamp milkweed

One of the keys to having monarchs—for their survival now and in the future—is having lots of milkweed. Because of modern changes, such as suburbanization and Roundup-Ready crops, there's a lot less milkweed than there was in the past. This is a disaster for monarchs since monarch caterpillars can eat nothing but milkweed.

No milkweed, no monarchs!

We want lots of monarchs, so we plant lots of milkweed for them to lay their eggs on. We've tried to maximize our milkweeds in a number of ways—especially since it's sometimes difficult to find them for sale or at least to find them for sale at an affordable enough price to buy more than just a few.

Pruning common milkweed ©Janet Allen
Pruning common milkweed helps keep it in control. (Be aware of keeping sap away from your eyes etc.!)

NOTE: The specific milkweed species I discuss are for my part of the country. Check the sidebar to find milkweeds native to other regions.

Purchasing milkweeds: All milkweeds are of the genus Asclepias. When we look for milkweed seeds or plants to purchase, we always look for this name. Sometimes nurseries are afraid to call them milkweeds since people shy away from anything with “weed” in its name, and because milkweeds have an undeservedly bad reputation.

Some nurseries name them something innocuous like “pink butterfly plant,” but that doesn't help people who are looking for milkweeds. Knowing the botanic name is very useful and helps us find the real milkweeds (if the grower actually uses these more correct names).

Tender regrowth ©Janet Allen
Monarchs love the tender leaves that regrow

Local ecotype: Now that there is an organized campaign to restore milkweed, local ecotypes of milkweed species are becoming available. If we were to buy any new milkweeds, we would look for plants grown from seeds responsibly collected in our own region.

An aside: We wish nurseries would offer six-packs of small milkweed plants rather than large, pricey single plants. They grow quickly enough that these large plants aren't necessary, and having one plant isn't going to really help much.

Milkweed in a field ©Janet Allen
Milkweed growing in a local field - unfortunately slated for development

How will a monarch find one isolated plant? Monarchs usually lay just one egg on a leaf, but they lay eggs on lots of leaves of more than one plant.

How could one or two plants be enough food for the caterpillars that develop from the eggs of even just one monarch? These caterpillars are eating machines!

Gathering milkweed seeds

Milkweed pod seeds ©Janet Allen
Milkweed seeds in their pod

To easily collect the milkweed seeds—i.e. getting the seeds without the fluff—we collect the pod when the pod has split, and it has just begun to open rather than waiting for the seeds' little “parachutes“ to start floating all over.

Wait until you see the pod starts to show the split, though. If you open the pod before it's ready, the seeds won't be ripe.

Stripping the seeds ©Janet Allen
Stripping the seeds

Then, we just hold the end and strip off the seeds. We're left with the not-yet-fluffy fluff in one hand, and the seeds in the other (or generally in a paper bag).

If we don't get to them before they're beginning to get fluffy, we just enjoy the fluff and collect the seeds anyway. It's just a little more of a challenge to separate the seeds from the fluff.

If you're not going to be sowing the seeds right away, store them in a paper envelope or bag, not plastic.

Growing milkweed from seed outside

Milkweed pod ©Janet AllenSwamp milkweed seed pod, more slender than the common milkweed pod most people think of; the butterfly weed pod is slenderer still

The easiest way is to sprinkle some seeds around in the fall after a killing frost and wait for spring. The seeds experience winter and know when it's time to get growing in spring.

Why wait until after a killing frost? Of course nature plants seeds whenever they ripen and drop from the plant, and plants can grow this way, but the little plants that germinate will face a killing frost. If you wait to sow the seeds after a killing frost, the seeds will be ready to grow early in the spring. And seeds often germinate better in cool soil.

This is probably the easiest method, but it's hard to remember to look for them in the spring and to recognize the seedlings as they emerge.

Of course, we do get a few seedlings popping up on their own around the yard, the seeds having been scattered by the wind the previous fall. Unlike some plants (e.g. jewelweed), though, swamp milkweed seedlings aren't a problem since there never seems to be very many. If they do pop up where we don't want them, we just pull them out, transplant them elsewhere, or pot them up to give away. The more people growing milkweeds the better!

Note: I've been pretty casual about this since I'm mostly growing some extra plants for my own yard, but local native plant professionals, such as Amanda's Garden and The Plantsmen Nursery, use seed starting mix and cover with ¼" of soil.

A quick and easy method

Filling pots ©Janet Allen
Sinking and filling pots for milkweeds

We wanted more than just the occasional seedling sprouting up at random, though, so we planted seeds ourselves. But rather than just sprinkling the seeds at random, we've started sowing them in pots in the fall after a killing frost, inserting a plant marker, then sinking the pots into the ground to wait for spring.

Why the pot? It reminds us that we planted something there, and that's where we'll find the seedlings.

We've generally put a little soil on top of the seeds, but Cullina says to surface sow. We'll experiment with both methods and see what happens.

Sowing milkweed ©Janet Allen
Sowing milkweed seeds in three pots

The PLANT LABEL is the important part! In the past, when I've started seeds this way but without a plant marker (after all, I obviously would know what I had planted…) come spring I've had no idea what was in the pot.

Many little seedlings came up the next spring, and even though they were a little crowded, they grew very well.

After procrastinating for a while, I took the next step and pulled the pots out of the ground. So far, so good. But then I just left them sitting there during one of our driest summers.

Milkweed pot ©Janet Allen
Starting milkweeds in a pot

After about a month, I took pity on them and guiltily knocked them out of the pot, untangled their roots, and planted them. The miracle is that even after this abuse they grew very well. I'm not recommending this kind of abuse, though. Think how much better they'll grow when I actually plant the little seedlings in a timely fashion.

From now on, I'll be sowing lots of pots and sinking them into the by-then empty vegetable garden. So far, this seems to be the easiest way to start milkweeds.

Growing milkweeds indoors

Cold stratifying seeds ©Janet AllenHere's what they look like before going into the plastic bag and into the refrigerator.

Why go to the trouble of growing them inside when it's so easy to start them outside? One reason is timing. As Amanda's Garden noted, seeds she started on November 11 germinated in late May. If you want to have larger plants for the beginning of the growing season, you'll need to start some plants inside.

It also is somewhat more predictable and it gives you a feeling of being in control of how many plants you produce (although we've had failures, including starting plants inside for Our Edible Garden).

If we grow them inside, we've found that cold stratification is really important if we want to get good germination and growth. The purpose is to trick the seeds into thinking they've been through winter. As everyone in Central New York knows, winter means cold and wet.

It's easy to fool the seeds. Just put them in a moist paper towel, then into a plastic bag and leave them in the refrigerator for 3-6 weeks or, as The Plantsmen Nursery recommends, just take them out after 30 days. Check on them occasionally; they may start germinating sooner, and you'll want to plant them then.

And that's all there is to the simple process with the big name of “cold stratification.”

Our milkweed experiment ©Janet AllenComparing cold-stratification to simply planting the seeds

Here's the results of our Asclepias incarnata (swamp milkweed) experiment. Guess which is the flat whose seeds were cold stratified.

In the flat on the left: We soaked half the seeds, and we simply planted half with no special treatment other than being on the cold porch all winter.

In the flat on the right: We cold-stratified the seeds. Virtually every seed came up, and much sooner than the seeds that were simply planted or soaked.

Milkweed seedlings under lights ©Janet AllenMilkweed seedlings under lights in the cellar

For a faster start, we start them indoors 6 weeks before the last frost date, growing them under fluorescent lights. This means that we put the seeds in the refrigerator as early as mid-February, so we can plant the seeds in late March. They'll start germinating about two weeks after planting.

If it's too late in spring to cold stratify, we've tried soaking the seeds in warm water for 24 hours before planting. In our experience, it wasn't much better than just planting the seeds, though. And though some recommend that the cold stratified seeds also be soaked in warm water for 24 hours, it didn't make a difference in our results, although it didn't hurt them either.

Milkweed seedlings closeup ©Janet AllenMilkweed seedlings closeup

We cover the seeds with about ¼" of soil or less. Cullina says they need light to germinate, so we'll try surface-sowing the next time and compare the two methods.

Sometimes we even start some later in the season. These are perennials, so getting off to a slower start the first year isn't a problem since we're just getting a head start for the following year. And milkweeds grow pretty quickly anyway.

Multiply by dividing

Tuber ©Janet Allen
A portion of a butterflyweed tuber (with penny for size)

CAUTION: This would definitely NOT apply to butterfly weed (A. tuberosa) since it has a long taproot, and taproots don't want to be divided.

On the positive side, this long taproot is what makes this variety of milkweed more drought-tolerant.

The plant to be divided ©Janet AllenThe plant to be divided

Although it doesn't seem to be an "officially" recommended way to get more milkweed plants, we've been successful in dividing swamp milkweed.

The plant to be divided. Each stem will become a new plant.

 The plant is dug up.  ©Janet AllenThe plant is dug up

Here's the root system. You can see that, unlike common milkweed (A. syriaca) that spreads underground, the swamp milkweed's roots are pretty self-contained and not inclined to spread.

This is one of the reasons (besides having beautiful flowers) that swamp milkweed is a very garden-worthy plant, as compared with common milkweed (A. syriaca).

Teasing roots apart  ©Janet AllenTeasing roots apart

Here I've teased apart the stalks, letting their roots untangle as I gently pulled.

The result ©Janet AllenThe result

Voila! Four plants where there had been one to three large ones and one small one (in the upper right).

Generally even these small ones grow well.

Common milkweed

Common milkweed seedlings ©Janet Allen
Common milkweed seedlings grown for our HGCNY Wild Ones group

I haven't tried transplanting or propagating common milkweed (A. syriaca), but others have. Here's what has been posted on the Monarch DPLEX listserv:

The propagation rhizome of A. syriaca grows about one inch deep. With young common milkweed, I cut a big circle around the plant, then go deep, and take out the whole mass. I pulled up about 3 feet of the rhizome and coiled it up in a flower pot with potting soil resulting in a vigorous lush milkweed bush. I think given the recent discussions I would try to cut it up and see if I could get many pots of milkweed.

In the fall and spring

Emerging milkweed ©Janet Allen
Milkweed emerging long after other plants have started growing

In the fall, I leave the dead stalks (perhaps cutting them back a bit just to make them shorter) for three reasons.

First, my milkweeds emerge later than many other plants. The first year I planted them, the following spring I thought they hadn't survived the winter since most other plants were already growing. But it turns out that they just take their time in the spring. The dead stalks I leave in the fall are a perfect plant marker so I know where to expect them to emerge in the spring.

Downy and milkweed(Enlarge) ©Janet Allen
A downy woodpecker finding a tasty morsel

Second, I leave them is that some birds find their fibers useful as a nest building material. In general, we clean up way too many bits of nature that birds and other creatures need for raising their young.

The third reason I leave at least some of the stalk standing is that these hollow stems are a good place for birds to find a tasty insect overwintering or to cache some seeds or insects of their own. Notice the small holes in the stalk where insects have exited (or have been pecked out).