CO-Horts Blog

Thursday, June 25, 2020

Milkweeds, Garden Design and Monarchs

Photo credit: Butterfly Gardening

Have you ever wondered which milkweed is really recommended for our home landscapes?  There are only a 100 species across the United States to select, but the best is Asclepias speciosa or Showy milkweed.  One word of caution is that Showy milkweed does need space because it is considered one of the tillering species of Asclepias.   

Showy milkweed grows one and a half feet to three feet tall with blue-green pubescent or hairy leaves producing flower clusters or umbels of star-like rose colored to purple flowers in the upper axils of the stem.  It grows best in full sun with moist, well-drained soil that can be course, medium or fine. Its native habitat ranges from dry to moist savannas, prairies, roadsides, old fields, and meadows according to Lady Bird Johnson Wildflower Center. The plant has a milky sap when you break the stem, or the stem is injured in some way.  This milky sap is a latex and except for Asclepias tuberosa is found as a characteristic of milkweeds. This sap containing toxins is a defense mechanism for the plant to make the leaves unpalatable. This plant serves as a host for monarchs while hummingbirds and other butterflies feed off the nectar.

Other milkweeds to add to your home landscape can be those with NON-Aggressive root systems which are as follows:
  1. Asclepias incarnata or Swamp milkweed which is a native perennial growing three to four feet tall in full sun and consistently moist soils.  Flowering in July through August its blossoms are pale pink to rose purple.  Suggested cultivars are ‘Cinderella’ have pink to dark pink, reflexed petals, and pink to white crowns. ‘Ice Ballet’ is a white-flowering cultivar. ‘Soulmate’ has deep rose-pink flowers.  For further reading:
  2. Asclepias tuberosa or Butterfly weed a perennial which grows one to three feet tall in full sun and soil that is average well-drained soils dry to medium moisture. It does well in poor dry soils and tolerates drought. 

What would be the best arrangement or placement of milkweed in a garden?  Dr. Adam Baker of the University of Kentucky did research and presented that research in a paper titled, “Colonization and usage of eight milkweed (Asclepias) species by monarch butterflies and bees in urban garden settings,” along with Daniel A Potter, also at the University of Kentucky. 

In short, the small garden plots that were designed for this study were laid out differently.  The first had tall Asclepias host plants around the perimeter of the garden and were more isolated in their spacing from one another. This design attracted a higher number of females laying eggs on the taller plants versus the shorter ones.  As quoted from the study, “Host finding and oviposition by monarchs are influenced by species, height, age, developmental stage, and condition of the milkweed in the field (Cohen & Brower 1982, Zalucki & Kitching 1982; Fischer et al. 2015). 

The other design layouts of scattering the Asclepias in the center of the small gardens did not fare as well for attracting monarchs and nor did creating a mixed combination of Asclepias with other plants. Placing taller Asclepias around the border and keeping the plants open and accessible was more beneficial to attracting monarchs.  By doing this it is believed to be helpful for the monarch’s visual perception.  

If you live in the right location and are interested in attracting monarchs to your garden, keep these plant arrangements in mind.  

Photo credit: Teresa Howes, Julesburg, CO.

 Written by CSU Linda Langelo, Horticulture Agent, Golden Plains Area