Lover Not Killer wants to save this butterfly species from extinction

Dear Avant Gardener, Monarchs were recently declared endangered and I’d like to do my part to save the intrepid monarch butterfly from extinction. However, I've also seen reports that monarch waystations can do more harm than good – for example, when planted too close to roads. Millions of monarchs evidently die on Texas highways. Is there any research on how to design a productive backyard monarch garden? — Lover Not Killer

Yes, there is real science behind designing a garden that supports monarch butterflies. And it probably isn’t what you imagine. Read on for fascinating research findings and seven rules summarizing recent studies. Then get planting. Citizen waystations like the one you’re planning are absolutely necessary to restore the two billion milkweed plants needed to stabilize the monarch population.

When “naturalistic” doesn’t nurture nature

You know those beautiful, “naturalistic” blends of species popularized by Dutch garden designer Piet Oudolf? Monarchs aren’t fans. They prefer structured beds with clear delineation among plants, according to research by urban landscape entomologist Daniel Potter at the University of Kentucky and his colleague Adam Baker. 

In fact, monarchs altogether avoided the sort of “matrix” advocated by Oudolf and others – where flowering perennials are surrounded by native grasses.

Female monarchs foraging in an open-field setting laid significantly more eggs on single milkweed plants that were accessible from top to bottom, without visual obstruction, compared to single plants surrounded by, but not touching, ornamental grasses of equal height. Milkweeds screened by grasses received almost no eggs over the 2-week trial. — Baker and Potter

What do monarchs want?

Blame monarchs’ poor eyesight. Or maybe fatigue from flying so far to find milkweed plants to host their eggs and larvae. (As you probably know, monarchs are dietary specialists – their larvae feed exclusively on milkweed species.) Monarchs lay more eggs on milkweed when it’s easy to find along their famous migratory path.

Total numbers of monarch eggs and larvae observed in twice-monthly visits to each garden were about five-fold higher in structured gardens with spacing between milkweeds and non-host plants than in non-structured gardens where those plants were closely intermixed, and similarly higher in gardens with unobstructed north-south access compared to ones where such access was obstructed by buildings. There was also a positive relationship between monarch abundance and proximity to the nearest structure. Other features of the gardens themselves (area, density of milkweeds, or nectar plants) or of the surrounding landscape within a 100 m radius did not explain a significant amount of variance in use by monarchs. — Baker and Potter, Frontiers in Ecology and Evolution (2019)

And Monarchs don’t just prefer structure, they prefer some structured arrangements more than others:

In both 2017 and 2018 monarch eggs and larvae were 2.5-4 times more abundant in gardens in which the milkweeds were planted around the perimeter, surrounding the nectar plants and grasses, than when the layout was reversed, with milkweeds in the garden interior, or when the milkweeds were randomly intermixed with other plants. — Baker and Potter

Seven rules for monarch gardens

Daniel Potter summarized this and other research in a recent Horticultural Research Institute webinar:

1. Place your monarch garden where most visible to monarchs flying north or south, preferably unimpeded by a building within 100 meters, perhaps close to the east or west side of your house or shed if there’s enough sun.

2. Avoid high traffic areas where butterflies can’t fly safely. Potter calls the highway monarch gardens you mention “ecological traps” – well-meaning but deadly.

3. Choose swamp milkweed east of the Rockies and showy milkweed (Asclepias speciosa) west. These significantly outperformed butterflyweed (Asclepias tuberosa) are less aggressive than other top performers, common milkweed or narrowleaf milkweed.

4. Plant milkweed on its own on the outside of the garden. Place nectar plants nearby in the interior of your monarch garden.

5. Do not erect butterfly houses – 80% of those tested were colonized by invasive European paper wasps, which prey on monarch caterpillars. Monitor for paper wasp nests nearby.

6. Do not plant tropical milkweed, also called Mexican butterflyweed (Asclepias curassavica). It does not die back in winter, so monarchs fail to migrate, making them susceptible to pathogens.

7. Forget about rearing monarchs in captivity. This breeds monarchs unfit for their 3,000-mile migration.

Breaking news

A study published this month in Biological Conservation found milkweed plants bought at nurseries may expose monarch caterpillars to harmful pesticide residues. Aimee Code, Pesticide Program Director at the Xerces Society for Invertebrate Conservation, advises "Just take steps to reduce pesticide exposure: cover new plants the first year, water heavily, discard the soil before planting, as it may be contaminated, and avoid pesticide use.”

— The Avant Gardener

Why, How, Wow!

Why?

What you plant and how you plant it makes a huge difference in the number of monarchs your garden attracts and nurtures.

How

Plant milkweed on its own around the perimeter of your garden and nectar plants in the middle. Monarch eggs and larvae were 2.5-4 times as abundant in gardens with milkweed planted this way (layout A) than in other configurations.

Wow!

Watching monarchs flying around (and breeding in) your garden is immensely rewarding, as is helping to save this species from extinction. Millions more citizen monarch waystations are needed.

Related Resources

• Interested in how citizen scientists helped get monarchs listed as endangered? Read this in Discover.

• Want to buy milkweed plants near you? Look at the Local Resources tab after putting your zip into the Audubon Native Plant Finder.

• Want to join with others to save monarchs? Register a waystation with Monarch Watch.