How Do Your Milkweeds Grow?

  • Mary, Mary quite contrary
  • How does your garden grow?
  • All the flowers, all the colors
  • All in a perfect row

Landscape architects and garden designers might disagree with Contrary Mary’s arrangement of flowers in a perfect row, but maybe it makes sense to monarch butterflies.

A recent publication by Adam Baker and Daniel Potter of the University of Kentucky reported that monarch eggs and larvae were 2.5–4 times more abundant in gardens where milkweeds were evenly spaced around the perimeter of the garden rather than intermixed with other nectar plants and grasses. You can read the full publication, Configuration and Location of Small Urban Gardens Affect Colonization by Monarch Butterflies in Frontiers of Ecology and Evolution, 05 December 2019 here: https://doi.org/10.3389/fevo.2019.00474.

The researchers established replicated gardens containing the identical mix of milkweeds, flowering nectar sources, and non-host ornamental grasses but arranged in three different spatial configurations as shown below.

 Figure 1 from Baker and Potter, 2018.
(A) milkweed plants on the perimeter of the garden; (B) milkweed on the interior of the garden; (C) no formal design. Bottom row, gardens of the various designs as they appeared in 2018.  Source: Figure 1 from Baker and Potter, 2018.

The milkweed plants were monitored for monarch colonization over two successive growing seasons.  They found 2.5 to 4 times more monarch eggs and larvae in garden design A, where the milkweeds were space 1-meter apart around the perimeter.  

The researchers also counted monarchs in 22 existing butterfly gardens in central Kentucky that were registered with Monarch Waystation or the Lexington Chapter of Wild Ones. Nine of the established gardens were “structured” with milkweeds planted in a relatively uniform pattern, set off by mulch, and separated from neighboring plants by 0.5 m or more. Thirteen gardens were “non-structured.” The milkweeds in “non-structured” gardens were haphazardly intermixed with nectar and non-host plants. Total numbers of monarch eggs and larvae observed in twice-monthly visits to each garden were about five-fold higher in structured gardens than in non-structured gardens where the plants were closely intermixed.

Additional data analyzed from the established gardens found there were more monarch eggs and larvae “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.”

In summary, garden layout “strongly influences the extent to which milkweeds are found and used” by monarch butterflies.  Milkweeds are more likely to be discovered and used for egg laying “when they are spatially separated from nectar and non-host plants as opposed to being closely intermixed with them.”

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