COLUMN | Milkweed + Honey: Milkweed can save the butterflies; but will it hurt us?

Published 12:00 am Wednesday, April 26, 2023

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Since April is now National Native Plant Month, it’s a good time to talk about a popular North American native, and part of the title of this column: milkweed. Or milkweeds, plural, since there are a couple hundred species of Asclepias around the world, including a handful of Northwest varieties.

These tall, striking, rather alien wildflowers are equal parts beloved and infamous, perceived as both a habitat darling and a toxic threat. Kind of like a looping roller coaster, or a sexy vampire. The truth is a little bit of both, but I think more people should plant it anyway.

THE “MILK” PART

Tear into a stem or leaf, and milkweed will ooze a white latex sap, like pale blood or thick milk. This sap, full of harmful cardiac glycosides, is part of the plant’s defenses. Its stickiness deters some insects simply by gluing their mouths shut, and its toxins make it unappealing to many others. However, one species is adapted to all this beautifully.

If you’re familiar with milkweed, it’s quite possibly thanks to monarch butterfly restoration campaigns. The iconic orange butterfly migrates back and forth from Mexico and Canada; the Pacific Northwest is not as big a stomping ground as California or eastern regions, but plenty of the butterflies do pass through. Unfortunately, across the western United States, the monarch population has plummeted to something like 1% of what it was in the 1980s. A big reason for this is habitat loss.

Many butterflies and other insects need specific plants to complete their life cycle; while some species can use a handful of hosts, monarchs rely on just one: milkweed. It is the only plant they lay eggs on, with the only leaves their larvae can eat. Why doesn’t the aforementioned death-milk bother them? In “Nature’s Best Hope: A New Approach to Conservation That Starts in Your Yard,” ecologist Douglas W. Tallamy explains:

Monarchs “block the flow of sap to milkweed leaves. … When a caterpillar first walks onto a milkweed leaf, it usually moves to the top of the leaf and starts to eat. If any latex sap starts to ooze from the wound, the caterpillar immediately stops eating, turns around, and crawls two-thirds of the way back up to the leaf, where it chews entirely through the large midrib. That simple act severs the main latex canals … With the canals blocked, all of the leaf tissue below the midrib wound become latex-free, and the monarch can eat them without gumming its mouthparts.”

Beyond that, monarchs carry enzymes that neutralize the harmful effects of any residual ingested sap, and they then carry the cardiac glycosides in their wings — whose bold orange color warns would-be predators of danger. The plant’s defenses become the butterfly’s. Britney Spears could write a whole song about monarchs, cause they’re toxic, too.

The plant that gives life to these revered butterflies can endanger much bigger creatures. Some ranchers dislike milkweeds in their grazing pastures, since they can be dangerous when ingested by livestock in large quantities, although the USDA points out it’s not very tasty, so “animals usually do not eat milkweed unless good forage is scarce or under conditions where plants freeze, etc.” (Some milkweeds have higher toxicity levels than others, too, and none of the species recommended here are the worst offenders.)

People shouldn’t snack on them, either; our hearts don’t like those pesky cardiac glycosides. And as with other oozy plants, milkweed sap can damage your eyes — always wear gloves while working in your garden and wash your hands after.

These warnings are important but don’t need to scare off most gardeners, in my opinion. A great number of common plants are poisonous; so don’t eat them!

THE “WEED” PART

Many a wildflower has been called a weed for the simple crime of being found more often in uncultivated areas than in fine gardening magazines. Milkweed faces this prejudice, along with a reputation for becoming “weedy” and spreading quickly from where you want it to where you don’t want it. In my experience, this notoriety is somewhat unfounded. I’ve had milkweeds in my yard for three years now and haven’t had to uproot any rhizomes. Perhaps since it’s established now, it will spread faster, but I have yet to regret my choice and in fact am thinking of putting in more. (Meanwhile, I’m already nervous about the truly weedy fireweed [Epilobium angustifolium] I planted just last year, based on the dozens of seedlings emerging in a 10-foot vicinity. I wanted it to spread, but not SPREAD spread.)

Species matters here, too. Common milkweed, which is most widespread in the eastern U.S., tends to be more aggressive, but showy milkweed, native to Oregon and Washington, sends out rhizomes more slowly. I have these two species in my bed and both have been fine. The common variety has sent up a couple of new rhizomes a few inches from the original plant; the showy, none at all.

If you’re concerned about weediness, choose showy milkweed. (It’s the local species you’re most likely to find in nurseries anyway.) It tends to be more compact than other varieties as well, growing about 3’x3′. You also could plant it in a contained area, as I did by putting it in a raised bed. Or you could grow it in your parking strip, surrounded by concrete, or try it in large planters.

RIGHT PLANT, RIGHT PLACE

You can help offset shrinking wild habitat by planting a patch of milkweed in your yard or community garden. Not only is it the crucial host for monarchs, but it feeds a variety of other butterflies, bees, moths, and insects as well. And it looks terrific.

Of course, every garden — and gardener — has its own conditions and needs. The mantra I learned as a Master Gardener is “right plant, right place.” If your yard is shady, you compulsively eat all your flowers, or starving cows wander your yard, then you might choose a different butterfly host. If you have a sunny spot you’re happy to let this strange beauty fill, then get thee to a nursery and bring home some milkweed.

The butterflies will thank you.

For regional milkweed guides, see the Xerces Society.

As some of my larger native wildflowers (milkweed and Douglas aster especially) have reached maturity, they’ve developed a problem: They’re very tall, and they lean over. This looks ugly. I call it the Perennial Flop. I’ve been developing a four-prong strategy to fight it:

  • WORSE SOIL. West of the Cascades, many natives are adapted to crummy, inconsistent clay soils. What they aren’t adapted to is my lush, loamy raised bed soil. (I originally planned to use it for vegetables.) The rich soil seems to cause things like milkweed to grow so tall that they topple over like a spoiled toddler denied a treat. So as counterintuitive as it seems to general gardening wisdom, I’m going to stop amending the soil for a year or two so it’s less nutrient dense, and hopefully the plants will become less coddled and more robust.
  • SUPPORT STRUCTURES. Instead of waiting until mid-summer to halfheartedly prop up fallen stems, I’m adding stakes and other supports as plants emerge in the spring and guiding them as they grow; hopefully this will make the supports more effective.
  • GIVE HAIRCUTS. This one makes me nervous, but a lot of folks recommend cutting perennials back a bit in early-to-mid spring before they’re too tall. They should recover fine but become bushier and stockier, rather than lanky and lackadaisical. I’m trying it, but I don’t like it!
  • ‘CRAMSCAPING.’ In some instances, I think planting wildflowers based on their mature size leaves too much open space around them for a few years. In an open meadow or in a woodland understory (the lower layer of plants under larger shrubs and trees), plants are competing for limited light and nutrients. Whereas in my garden, they are pampered in a space of their own. So this year I’m trying to plant more small annuals around the larger perennials (closer than they’re “supposed” to be) to see if it helps them assert themselves. We’ll see! 

Do you have a trick for managing the Perennial Flop? Let me know at milkweedandhoney@pamplinmedia.com.